Height velocity and IGF‐I assessment in the diagnosis of childhood onset GH insufficiency: do we still need a second GH stimulation test?

OBJECTIVE: The diagnosis of GH insufficiency (GHI) in childhood is not straightforward. Our aim was to test the sensitivity and specificity of height velocity (HV), IGF-I, IGFBP-3 and GH stimulation tests alone or in combination in the diagnosis of GHI. DESIGN: A retrospective review of patients with GHI and idiopathic short stature (ISS) diagnosed in our centre and followed up to the completion of linear growth. PATIENTS: Thirty-three GHI children and 56 children with ISS were evaluated. GHI diagnosis was based on fulfilment of anthropometric, endocrine and neuroradiological criteria: stature < or = -2 z-score, delayed bone age (at least 1 year), GH peak response to at least two different provocative tests < 10 micro g/l (20 mU/l), brain MRI positive for hypothalamus-pituitary abnormalities, catch-up growth during the first year of GH replacement therapy > or = 75th centile, peak GH response to a third provocative test after growth completion < 10 micro g/l (20 mU/l). Children with anthropometry resembling that of GHI but with peak GH responses > 10 micro g/l (20 mU/l) were diagnosed as ISS. MEASUREMENTS: All subjects underwent standard anthropometry. GH secretory status was assessed by clonidine, arginine and GHRH plus arginine stimulation tests. IGF-I and IGFBP-3 circulating levels were measured by immunoradiometric assay (IRMA). The following cut-off values were chosen to discriminate between GHI and nonGHI short children: HV < 25th centile over the 6-12 months prior to the initiation of GH therapy, peak GH responses < 10 or < 7 micro g/l (< 20 or < 14 mU/l) and IGF-I and IGFBP-3-values < -1.9 z-score. Sensitivity (true positive ratio) and specificity (true negative ratio) were evaluated. RESULTS: Taking 10 micro g/l (20 mU/l) as the cut-off value, sensitivity was 100% and specificity 57% for GH provocative tests, whereas taking 7 as the cut-off value, sensitivity was 66% and specificity rose to 78%. Sensitivity was 73% for IGF-I and 30% for IGFBP-3 measurement, whilst specificity was 95% for IGF-I and 98% for IGFBP-3 evaluation. HV assessment revealed a sensitivity of 82% and a specificity of 43%. When HV and IGF-I evaluations were used in combination, sensitivity reached 95% and specificity 96%. When both HV and IGF-I are normal (26% of our subjects) GHI may be ruled out, whereas when both the indices are subnormal (23%) GHI is so highly likely that the child may undergo only one GH provocative test and brain MRI and, thereafter, may begin GH therapy without any further test. In case of discrepancy, when IGF-I is normal and HV < 25th centile (44% of children), due to the relatively low sensitivity of IGF-I assessment and low specificity of HV, the patient should undergo GH tests and brain MRI. Finally, in the rare case of HV > 25th centile and subnormal IGF-I-values (7%), due to the high specificity of IGF-I measurement, the child should undergo one provocative test and brain MRI for the high suspicion of GHI. CONCLUSIONS: Our results suggest that a simple assessment of HV and basal IGF-I may exclude or, in association with only one stimulation test, confirm the diagnosis of GH insufficiency in more than half of patients with short stature.     

The assessment of growth hormone status in normal young adult males using a variety of provocative agents

OBJECTIVE In adults, there are few data regarding GH responses to provocative stimuli other than insulin-induced hypoglycaemia. We have compared the GH response to four different growth hormone secretagogues and placebo in normal healthy adult males. DESIGN This was a prospective, randomized, placebo-controlled study in 18 normal male subjects. After an overnight fast, an intravenous cannula was inserted into the arm of each subject and a blood sample was taken for GH at ?30, ?15, and 0 minutes. Four provocative agents (intravenous insulin 0.2 IU/kg; intravenous arginine 20 g/m² as an infusion over 30 minutes; oral clonidine, either 100 or 200 μg; intramuscular glucagon 1 mg) and placebo were administered to each subject in a randomized manner on different days. Further blood samples were taken at 15-minute intervals for 180 minutes for GH estimation. RESULTS The median (range) GH peak response for each agent was insulin 107.7 (28.1–200) mU/l; arginine 22.3 (3.1–72.9) mU/l; glucagon 42 (11.8–200) mU/l; 100 μg clonidine 7.2 (<1–22.2) mU/l; 200 μg clonidine 8.2 (1.1–88) mU/l and placebo 2.4 (<1–30.2) mU/l. The peak GH response to insulin-induced hypoglycaemia (ITT) was significantly greater than for any other agent (P<0.0001). The peak GH response to glucagon was significantly greater than for arginine (P<0.05), clonidine at 100 and 200 μg (P<0.01) and placebo (P<0.01). The peak GH response following administration of arginine was significantly greater than for clonidine 100 and 200 μg (P<0.05), and placebo (P<0.01). The peak GH response following clonidine 200 μg was not significantly greater than following clonidine 100 μg (P=0.38) or placebo. On an individual basis two, six and 15 of 18 subjects failed to achieve a peak GH level of >20 mU/l to glucagon, arginine and clonidine respectively. In complete contrast only one subject achieved a peak response of less than 40 mU/l (28.1 mU/l) to ITT. CONCLUSIONS The most profound GH release is seen after insulin-induced hypoglycaemia. Glucagon appears to be more effective at inducing GH release than arginine. Clonidine at a dose of 100 or 200 μg is no more effective than placebo.     

Re-assessment of growth hormone secretion in young adult patients with childhood-onset growth hormone deficiency

OBJECTIVE: Patients with childhood-onset GH deficiency (coGHD) need retesting in late adolescence or young adulthood to verify whether they need to continue GH treatment. For this purpose the Growth Hormone Research Society (GRS) recommends the insulin tolerance test (ITT), or as an alternative the arginine + growth hormone releasing hormone test (ARG + GHRH test) as a diagnostic tool in adolescents and adults. However, there are no standardized cut-off levels based on normal GH secretion for determining GHD vs. GH sufficiency in young adults for the ITT, the ARG + GHRH test or the pyridostigmine + GHRH (PD + GHRH) test, a further new GH stimulation test. PATIENTS AND MEASUREMENTS: We studied 43 patients (28 with organic coGHD, 15 with idiopathic coGHD; 30 males, 13 females; aged 20.4 years, range 16.2-25.4; body mass index 23.5, range 16.3-35.8) using the ARG [0.5 g/kg intravenously (i.v.)] + GHRH (1 micro g/kg i.v.) test, the PD (120 mg orally) + GHRH (1 micro g/kg i.v.) test and the ITT (0.1 IU/kg i.v.) and compared these data with the results of 40 healthy age- and weight-matched volunteers. RESULTS: The GH response in patients was significantly lower than in healthy controls: ARG + GHRH test, 0.8 micro g/l (interquartile range 0.3-2.6) vs. 51.8 micro g/l (32.6-71.2) in controls (P < 0.0001); PD + GHRH test, 0.9 micro g/l (0.3-1.9) vs. 40.4 micro g/l (27.1-54.4) in controls (P < 0.0001); ITT, 0.1 micro g/l (0.0-0.8) vs. 20.3 micro g/l (14.7-31.7) in controls (P < 0.0001). In the ARG + GHRH test we found a diagnostic sensitivity of 100% and a specificity of 97.5% for a cut-off range from 15.1 to 20.3 micro g/l, in the PD + GHRH test a sensitivity of 100% and a specificity of 97% (cut-off range 9.1-13.1 micro g/l) and in the ITT a sensitivity and specificity of 100% each within a cut-off range from 2.7 to 8.8 micro g/l. CONCLUSION: There were no marked differences in sensitivity and specificity in young adults among ARG + GHRH test, PD + GHRH test and the ITT in assessing GH secretion. Because of the lack of side-effects, the ARG + GHRH test is the recommended method for re-evaluation of coGHD in young adults when pituitary GHD is suspected. Furthermore, in adult patient groups where organic pituitary coGHD is common, the ITT may be completely replaced by the ARG + GHRH test. Because of the predominance of hypothalamic GHD in childhood, the ITT is commonly performed for the re-evaluation of patients with childhood-onset GHD because of its mechanism of GH stimulation. The present results confirm the high discriminatory capability of the ITT in young adults.     

What is a normal stimulated growth hormone concentration?

In a retrospective analysis, we have compared the response of serum GH concentration to insulin-induced hypoglycaemia in 148 short prepubertal children (114 males, 34 females) aged between 3.9 and 11.9 years with the growth rate of the individual to determine 'cut-off' values for the diagnosis of GH insufficiency. Sixty-three children grew with a height velocity standard deviation score (SDS) greater than -0.8 (group 1), which represents the growth velocity of children progressing along or closely parallel to the third height centile. Eighty-five children had a height velocity SDS of less than -0.8 (group 2). Median peak serum GH concentration responses to insulin-induced hypoglycaemia were 19.9 mU/l (range 1.5-54.4) in group 1 and 9.9 mU/l (range 0.7-46.2) in group 2 (Mann-Whitney; P less than 0.001). Using growth rate as the determinant of normality, the efficiency, sensitivity and specificity of the insulin-induced hypoglycaemia test were calculated using different serum GH concentration cut-off values to diagnose GH insufficiency. In our (Hybritech) assay, a cut-off value of 13.5 mU/l provided optimal performance in terms of efficiency (66%), sensitivity (64%) and specificity (70%). The response of serum GH concentration to insulin-induced hypoglycaemia in short children growing at different growth rates was continuous. Each laboratory measuring serum GH concentrations needs to construct its own 'normal' cut-off value.     

ARGININE POTENTIATES THE GHRH- BUT NOT THE PYRIDOSTIGMINE-INDUCED GH SECRETION IN NORMAL SHORT CHILDREN. FURTHER EVIDENCE FOR A SOMATOSTATIN SUPPRESSING EFFECT OF ARGININE

To investigate the mechanism underlying the GH-releasing effect of arginine (ARG), we studied the interactions of ARG (0.5 g/kg infused i.v. over 30 min) with GHRH (1 microgram/kg i.v.) and with pyridostigmine (PD, 60 mg orally) on GH secretion in 15 children and adolescents with familial short stature (5.1-15.4 years). In a group of eight subjects ARG induced a GH increase not statistically different to that observed after GHRH (peak, mean +/- SEM: 38.0 +/- 10.4 vs 64.0 +/- 14.4 mU/l). The combined administration of ARG and GHRH led to GH levels (101 +/- 15.2 mU/l) higher than those observed after GHRH (P less than 0.025) or ARG alone (P less than 0.001) and overlapping with those recorded after combined PD and GHRH administration (111 +/- 22.4 mU/l). In the other seven subjects, ARG and PD administration induced a similar GH response either when administered alone (25.2 +/- 13.6 and 27.8 +/- 4.0 mU/l, respectively) or in combination (33.8 +/- 5.4 mU/l). In conclusion, our results show that in children ARG administration potentiates GHRH- but not PD-induced GH increase. These findings agree with the hypothesis that the GH-releasing effect of both ARG and PD is mediated via the same mechanism, namely, by suppression of endogeneous somatostatin release. Combined administration of either ARG or PD with GHRH has a similar striking GH-releasing effect which is clearly higher than that of GHRH alone.     

A simple diagnostic test using GH-releasing peptide-2 in adult GH deficiency

OBJECTIVE: The international, first-line diagnostic test for adult GH deficiency is the insulin tolerance test (ITT), which is contraindicated in some patients due to severe adverse events. Alternatives such as GH-releasing hormone combined with arginine or GH-releasing peptides (GHRP) have been proposed. We validated the use of GHRP-2 for diagnosing adult GH deficiency (GHD). METHODS: Seventy-seven healthy subjects and 58 patients with peak GH<3 microg/l by ITT were enrolled. After overnight fasting, a 100 microg dose of GHRP-2 was administered intravenously; blood samples were taken during the subsequent 2 h and GH measured by immunoradiometric assay. RESULTS: Serum GH peak occurred within 60 min after GHRP-2 administration in all subjects. GH responses to GHRP-2 were not affected by gender, but were slightly lower in elderly subjects and those with adiposity, although these did not influence diagnosis of GHD. Repeated tests showed favourable reproducibility. Peak GH concentrations after GHRP-2 were significantly (P<0.001) lower in patients (1.36+/-2.60 microg/l) than the healthy group (84.6+/-60.9 microg/l) with no difference between hypothalamic and pituitary diseases. Serum GH concentration at the point where sensitivity of response crossed with specificity ranged from 15 to 20 microg/l. A cut-off value of 15 microg/l for diagnosing GHD with GHRP-2 corresponded to the diagnostic value of 3 microg/l in the ITT. CONCLUSIONS: The GHRP-2 provocative test showed favourable reproducibility and was mildly influenced by age and adiposity. Severe GH deficiency could be diagnosed with high reliability using a 15 microg/l (9 microg/l when GH calibrated with recombinant World Health Organization 98/574 standard) cut-off for peak GH concentration.     

The nadir growth hormone after an octreotide test dose predicts the long-term efficacy of somatostatin analogue therapy in acromegaly

OBJECTIVE: In the treatment of acromegaly, a 'test dose' of octreotide is recommended prior to the use of depot somatostatin analogue (SSA) therapy. However, there remains no consensus regarding the criteria that predict a response to treatment. The ability to select patients who may benefit most from medical therapy is potentially of great value in clinical practice. The aim of the study was to determine the predictive value of both the nadir GH and the mean GH following an octreotide test dose in identifying patients who subsequently achieved disease remission with depot SSA therapy. Remission was defined as a mean GH < 5 mU/l (< 2 microg/l). DESIGN: Retrospective case-control study. PATIENTS: A group of 41 patients with acromegaly underwent an octreotide test dose where GH was measured hourly for a total of 6 h following an injection of octreotide 50 microg subcutaneously. Nadir GH and mean GH following the octreotide test dose were determined. Thirty-three patients were subsequently treated with depot SSA therapy and mean GH and IGF-I levels were determined at follow-up. RESULTS: The nadir GH demonstrated superior predictive power to that of mean GH across a range of GH cut-off values. A nadir GH < 5 mU/l demonstrated 80% sensitivity and 83% specificity in predicting remission with depot SSA therapy. A nadir GH < 10 mU/l demonstrated 100% sensitivity and 56% specificity. CONCLUSIONS: The nadir GH following an octreotide test dose is a useful predictive marker of achieving disease remission with depot SSA therapy used as either a primary or an adjuvant agent.     

THE INTERACTION BETWEEN CLONIDINE AND GROWTH HORMONE RELEASING HORMONE IN THE STIMULATION OF GROWTH HORMONE SECRETION IN MAN

Six normal adult males were given clonidine and GHRH either separately, or in combination, in random order. The peak serum GH concentrations elicited by clonidine or GHRH were variable but one factor influencing the GH response to GHRH was the GH secretory status in the hour prior to the administration of the GHRH. Peak serum GH concentrations attained were significantly greater when serum GH concentrations were rising (mean 52.9 mU/l, SD 17.2) than if they were falling (mean 27.5 mU/l, SD 13.3) or unchanged/undetectable (mean 20.6 mU/l, SD 9.8) (one-way ANOVA, F = 8.77; P = 0.004). The GH response to clonidine was not influenced by the secretory status in the hour prior to administration of clonidine. Pretreatment with clonidine did not augment the peak serum GH response to GHRH but the direction of response was more predictable than when GHRH was administered separately or repeatedly. Prior treatment with GHRH(1-29)-NH2 led to a marked attenuation of the peak serum GH response to clonidine. These results suggest that the alpha-2 adrenergic agonists probably stimulate GH secretion through pathways other than just GHRH.     

Diagnosis of growth hormone deficiency after pituitary surgery: the combined acipimox/GH-releasing hormone test

OBJECTIVE: Reduction of plasma free fatty acids leads to enhanced GH response after stimulation by GH-releasing hormone (GHRH). We studied the clinical usefulness of combined administration of acipimox and GHRH for the diagnosis of GH deficiency. DESIGN: We evaluated 35 patients [mean age 53.0 years; mean body mass index (BMI) 26.7 kg/m2] after pituitary surgery. We compared GH responses after acipimox and GHRH with the GH response during an insulin tolerance test (ITT) and, in a subgroup of 12 patients, with the GHRH/arginine test. The acipimox/GHRH test was additionally performed in 21 control subjects (mean age 53.8 years; mean BMI 24.7 kg/m2). RESULTS: In the patients, the mean (+/- SEM) peak GH was almost four-fold higher after acipimox/GHRH (6.94 +/- 1.07 microg/l, range 0.46-23.1; P < 0.001) and after GHRH/arginine (8.32 +/- 1.23 microg/l, range 1.1-49.2; P < 0.001) than after ITT (1.84 +/- 0.46 microg/l, range 0.01-11.9). According to the ITT, 29 patients were severely GH deficient (peak GH < 3.0 microg/l). Peak GH levels after acipimox/GHRH in controls ranged from 7.5 to 78.4 microg/l (mean 29.3 +/- 3.5). GH peak values during the acipimox/GHRH test were significantly correlated with values from the ITT (r = 0.63, P < 0.01) and GHRH/arginine test (r = 0.87, P < 0.001). Areas under the curve were also correlated. According to generally accepted cut-off peak GH levels for the ITT and GHRH/arginine test, a GH peak exceeding 11.2 micro g/l excludes severe GH deficiency after acipimox/GHRH. Our control data indicate that the cut-off level is lower at older age. CONCLUSIONS: The acipimox/GHRH test leads to GH responses similar to those of the GHRH/arginine test, and to higher peak GH values if compared with the ITT. The acipimox/GHRH test is a potential additional tool to detect GH deficiency in patients with pituitary disease, in particular in patients with a perturbation of fatty acid metabolism.     

Cholinergic modulation of growth hormone responses to growth hormone-releasing hormone in uraemic patients on peritoneal dialysis

BACKGROUND: Hypothalamic cholinergic neurotransmission plays a major role in the regulation of GH secretion. Pyridostigmine, a cholinesterase inhibitor, is able to decrease hypothalamic somatostatinergic tone and release GH in normal subjects. Blockade of muscarinic receptor with pirenzepine blunts the GH release in several clinical situations. However, little information is available on the role played by central cholinergic pathways in GH regulation in uraemic patients. OBJECTIVE: We aimed to assess GH responses to GHRH after pretreatment with pyridostigmine and pirenzepine in a group of uraemic patients undergoing peritoneal dialysis (PD). GH responses of the patients treated with recombinant human erythropeitin (rhEPO) were compared to patients without treatment. DESIGN: We studied 14 male patients on PD and nine control subjects. All subjects underwent three endocrine test in random order after an overnight fast. Each subject received GHRH (100 microg, i.v. in bolus at 0 minutes). Sixty minutes before the injection of GHRH subjects were given oral placebo, pyridostigmine (120 mg), or pirenzepine (100 mg). MEASUREMENTS: Blood samples for GH were collected at -60, 0, 15, 30, 45, 60 and 90 minutes The hormonal secretory responses were studied by a time-averaged (area under the curves, AUC) and time-independent (peak values) analysis. RESULTS: Baseline GH concentrations were similar in patients and controls. GH responses to placebo plus GHRH were also comparable in patients and controls (peak 26.6 +/- 3.8 vs. 33.2 +/- 4.4 mU/l, AUC 28.2 +/- 3.4 vs. 27.8 +/- 4.6 mU/h/l). Pyridostigmine administration induced a significant potentiation of GH responses to GHRH both in patients (peak 43.2 +/- 5.2 mU/l, AUC 47.6 +/- 6.0 mU/h/l; P < 0.01) and in control subjects (peak 79.2 +/- 8.6 mU/l, AUC 78.0 +/- 9.4 mU/h/l; P < 0.01). However, the increment in GH peak and AUC was significantly (P < 0.05) greater in controls in relation to values found in patients. Pirenzepine administration induced an abolishment of GH release after GHRH stimulation both in PD patients (peak 5.4 +/- 2.6 mU/l, AUC 6.0 +/- 2.4 mU/h/l; P < 0.01) and in healthy controls (peak 3.8 +/- 0.6 mU/l, AUC 4.0 +/- 0.4 mU/h/l; P < 0.05). Responses to pyridostigmine plus GHRH and pirenzepine plus GHRH were similar in patients on chronic therapy with recombinant human erythropeitin and in patients without rhEPO therapy. CONCLUSION: These results suggest that the cholinergic regulation of GH release is preserved in uraemic patients on peritoneal dialysis. The significantly lower increase in GH response to GHRH induced by pyridostigmine suggests that cholinergic stimulatory tone is attenuated in patients in relation to control subjects. Long-term therapy with rhEPO seems not to affect GH responses to cholinergic stimulation or blockade.     

The cut-off limits of the GH response to GH-releasing hormone-arginine test related to body mass index

OBJECTIVE: The diagnosis of growth hormone (GH) deficiency (GHD) in adults is based on a reduced peak GH response to provocative tests, such as the insulin tolerance test (ITT) and the GH-releasing hormone-arginine (GHRH-ARG) test. However, the cut-off limits of peak GH response in lean subjects are not reliable in obese patients; this is noteworthy since adult GHD is often associated with obesity. Aim of this study was to evaluate the diagnostic cut-off limits of peak GH response to the GHRH-ARG test in overweight and obese as well as in lean population. DESIGN AND METHODS: The GH responses to the GHRH-ARG test were studied in 322 patients with organic hypothalamic-pituitary disease and in 318 control subjects. Patients were subdivided into two groups on the basis of the number of pituitary hormone deficits, except for GH deficiency: (a) patients with total pituitary hormone deficit (TPHD) and (b) patients without or with no more than two pituitary hormone deficits (PHD). Both patients and control subjects were divided into three subgroups according to body mass index (BMI): lean (BMI <25 kg/m(2)), overweight (BMI > or = 25 and <30 kg/m(2)) and obese (BMI > or =30 kg/m(2)). TPHD patients were assumed to be GH deficient, whereas PHD patients may include subjects with either normal or impaired GH secretion. The statistical analysis was carried out by the Receiver-Operating Characteristic curve analysis (Medcalc 7.2). The diagnostic cut-off points were calculated for lean, overweight and obese subjects to provide optimal separation of GH-deficient patients and control subjects according to two criteria: (1) a balance between high sensitivity and high specificity; (2) to provide the highest pair of sensitivity/specificity values for GH deficiency. RESULTS: In the lean population the best pair of values, with highest sensitivity as 98.7% and highest specificity as 83.7%, was found using a peak GH cut-off point of 11.5 mug/l. In the overweight population the best pair of values, 96.7 and 75.5%, respectively, was found using a peak GH cut-off point of 8.0 mug/l. In the obese population the best pair of values, 93.5 and 78.3%, respectively, was found using a peak GH cut-off point of 4.2 mug/l. Applying the above mentioned cut-off points, among PHD patients we found that 80 subjects (72%) were GHD whereas 31 (28%) had normal GH secretion. CONCLUSIONS: In conclusion the GHRH-ARG test is a reliable tool for the diagnosis of adult GH deficiency in lean, overweight and obese patients, provided that specific BMI-related cut-off limits are assumed.     

The prevalence of severe growth hormone deficiency in adults who received growth hormone replacement in childhood

OBJECTIVE The few previous studies in which reassessment of GH status has been carried out in young adults treated with GH therapy for childhood GH deficiency concentrated on determining the incidence of ‘transient GH deficiency’. As the benefits of GH replacement therapy in adults become increasingly appreciated, it is likely that GH therapy started in childhood for GH deficiency will be continued into adult life in many of those with severe GH deficiency. The aim of this study is to determine how many patients who received GH replacement therapy in childhood until completion of growth have GH deficiency severe enough to be considered for GH replacement therapy in adult life. DESIGN Retrospective analysis of the peak GH responses to provocative stimuli performed at the time of diagnosis of GH deficiency in childhood and at the completion of growth after GH replacement therapy had been stopped. PATIENTS Eighty-eight adults (49 male, 39 female) who had received GH therapy in childhood for a diagnosis of GH deficiency. The aetiology of the GH deficiency included craniopharyngioma, radiation induced associated with either a cerebral tumour or acute lymphoblastic leukaemia, histiocytosis-X and idiopathic. MEASUREMENTS In childhood the original diagnosis of GH deficiency was based biochemically on the failure of the peak GH response to reach 20 mU/l during two provocative tests in 59 of the 88 patients and to a single test in the remaining 29. A total of 147 tests were performed, the most common being an insulin tolerance test (ITT, n= 72) and an arginine stimulation test (AST, n= 53). At reassessment in young adult life 146 tests were performed (74 ITT, 64 AST). Severe GH deficiency was defined arbitrarily as a peak GH response of less than 9 mU/l to a single (n = 33) or to two (n = 55) pharmacological stimuli. RESULTS By definition all patients were considered GH deficient at the time of initial diagnosis. A peak GH response of less than 9 mU/l was seen in 64.8% at initial assessment and 60.2% at reassessment. Analysis in aetiological terms, however, showed that between assessments the incidence of severe GH deficiency increased in the group of radiation induced (48.8 vs. 55.8%) but decreased in the idiopathic group (78.1 vs. 53.1%). Out of the 55 patients who underwent two tests at reassessment, 47.3% of those with a GH peak less than 9 mU/l at one test had a GH peak greater than 9 mU/l at the second test. Fifteen of the 55 patients had additional pituitary hormone deficiencies and all 15 had a GH peak below 9 mU/l in both tests. CONCLUSIONS Our study suggests that all children who have received GH replacement therapy in childhood should undergo reassessment of GH status in young adult life. Between 40 and 60% of such patients merit consideration for GH therapy in adult life depending on the definition of severe GH deficiency in use. Patients with isolated GH deficiency should undergo two provocative tests of GH secretion, but those with additional anterior pituitary hormone deficiencies require only one test at reassessment.     

The value of an acute octreotide suppression test in predicting long-term responses to depot somatostatin analogues in patients with active acromegaly

BACKGROUND: The long-acting depot somatostatin analogues [octreotide LAR (LAR) and lanreotide (LAN)] are among the most effective available medical therapies for acromegaly. However, published data on a biochemical test suitable for predicting the responsiveness to these depot agents are lacking. AIM: To investigate the value of an acute octreotide suppression test (OST) in predicting the responses to treatment with long-acting somatostatin analogues in patients with active acromegaly. PATIENTS AND METHODS: Thirty patients with active acromegaly [mean GH in GH day curve (GHDC) > 5 mU/l] were subjected to an OST [hourly GH measurements for 6 h following 100 microg subcutaneous (s.c.) octreotide]. Subsequently, 14 patients were treated with LAR, 10 with LAN and 6 received both drugs at different times. The final response to treatment was evaluated when the subjects had achieved 'safe' GH levels (mean GH < 5 mU/l) or after receiving the maximal dose of each drug (maximum duration of treatment 6 months). RESULTS: The nadir GH values during the OST were 2.6 +/- 2.5 mU/l (mean +/- SD, range 0.2-8.7) with a percentage fall of 84.8 +/- 15.7% (mean +/- SD, range 26-99%) from the baseline levels (26.2 +/- 31.5 mU/l, mean +/- SD). All the patients except one showed a decrease of greater than 50%. The mean time to achieve the nadir GH value was 3.8 +/- 1.6 h (mean +/- SD, range 1-6). The nadir GH levels showed a positive correlation with both pre-treatment (i.e. before commencing LAN or LAR) GH values during the GHDC (r = 0.63, P < 0.01) and IGF-I levels (r = 0.56, P < 0.05). The nadir GH values during the OST showed a positive correlation with the achieved mean GH levels in patients treated with LAR (r = 0.66, P < 0.01) but not in the ones treated with LAN. The criterion of GH < 5.25 mU/l during the OST had sensitivity 100%, specificity 80%, positive predictive value (PPV) 94% and negative predictive value (NPV) 100% in predicting achievement of 'safe' GH levels in patients treated with LAR. A less optimal prognostic profile was obtained for subjects treated with LAN with the criterion of GH < 6.05 mU/l during the OST providing sensitivity 92%, specificity 67%, PPV 92% and NPV 67%. The above cut-off GH levels had a PPV of only 77% and 60% in predicting normalization of IGF-I on treatment with LAR or LAN, respectively. CONCLUSIONS: The OST is a reliable tool for the selection of patients with active acromegaly who will achieve 'safe' GH levels on therapy with LAR. Its prognostic profile is less optimal for patients treated with LAN. If GH values during the test fall < 5.25 mU/l (in case of LAR treatment) or < 6.05 mU/l (in case of LAN treatment), there is a 92-94% chance of subsequently achieving 'safe' GH levels after up to 6 months treatment with either of these agents.     

The effectiveness of arginine + GHRH test compared with GHRH + GHRP-6 test in diagnosing growth hormone deficiency in adults

OBJECTIVE: The objective of this study is to investigate the performance of two novel tests in diagnosing growth hormone deficiency in adults. PATIENTS: Fifty patients presenting with long-standing hypopituitarism and two control groups consisting of 50 healthy subjects in each group [age-, sex- and body mass index (BMI)-matched] participated in a multicentre study. All underwent two provocative tests on different days within 3 months apart: (i) a combined GHRH + GHRP-6 test and (ii) arginine + GHRH test. Main outcome measures were sensitivity, specificity and areas under receiver operating characteristic curves (ROC) for GHRH + GHRP-6 and arginine + GHRH tests in the diagnosis of GH deficiency in adults. RESULTS: A peak GH level after GHRH + GHRP-6, under 15.0 microg/l had a sensitivity of 94.4% and specificity of 98.8% for diagnosing GHD and area under the ROC curve was 0.99 (95% confidence interval 0.95-0.99). For peak GH levels after arginine + GHRH, a level under 9.6 microg/l had a sensitivity of 88.4% and specificity of 95% and area under the ROC curve of 0.96 (95% confidence interval 0.91-0.98). The relationship between the increment in serum GH following GHRH + GHRP-6 and arginine + GHRH test was positive, i.e. r = 0.749, P = 0.001.Thus, there was high concordance between both tests. CONCLUSION: Both GHRH + GHRP-6 and/or arginine + GHRH test may serve as an alternative to the ITT in diagnosing GHD in adults.     

Comparisons among old and new provocative tests of GH secretion in 178 normal adults

Classical provocative stimuli of GH secretion such as insulin-induced hypoglycaemia, arginine, clonidine, glucagon and levodopa have been widely used in clinical practice for approximately 30 years. On the other hand, in the last 10 years new potent stimuli of GH secretion have been proposed, but an extensive comparison with the classical ones has rarely been performed, at least in adults. In order to compare the GH-releasing activity of old and new provocative stimuli of GH secretion, and to define the normative values of the GH response, in 178 normal adults (95 males, 83 females; age range: 20-50 years, all within +/-15% of their ideal body weight), we studied the GH response to: insulin-induced hypoglycaemia (ITT, 0.1IU/kg i.v.), arginine (ARG, 0.5g/kg i.v.), clonidine (CLO, 300 microg/kg p.o.), glucagon (GLU, 1mg i.m.), pyridostigmine (PD, 120mg p.o.), galanin (GAL, 80pmol/kg per min), GH-releasing hormone (GHRH, 1 microg/kg i.v.), GHRH+ARG, GHRH+PD, hexarelin, a GH-releasing protein (HEX, 2 microg/kg i.v.) and GHRH+HEX (0.25 microg/kg i.v.). The mean (+/-s.e.m.) peak GH response to ITT (21.8+/-2.8, range: 3.0-84.0 microg/l) was similar to those to ARG (18.0+/-1.6, range: 2.9-39.5 microg/l) or GLU (20. 5+/-2.2, range: 10.6-36.9 microg/l) which, in turn, were higher (P<0. 001) than those to CLO (8.2+/-1.6, range: 0.3-21.5 microg/l), PD (9. 6+/-1.1, range: 2.2-33.0 microg/l) and GAL (9.3+/-1.1, range: 3.9-18. 3 microg/l). The GH response to GHRH (19.1+/-1.5, range: 2.7-55.0 microg/l) was similar to those after ITT, ARG or GLU but clearly lower than those after GHRH+ARG (65.9+/-5.5, range: 13.8-171.0 microg/l) and GHRH+PD (50.2+/-4.6, range: 17.7-134.5 microg/l) which, in turn, were similar. The GH response to HEX (55.3+/-5.5, range: 13.9-163.5 microg/l) was similar to those after GHRH+ARG and GHRH+PD but lower (P<0.001) than that after GHRH+HEX (86.0+/-4.3, range: 49. 0-125.0 microg/l) which was the most potent stimulus of GH secretion. In this adult population the third centile limits of peak GH response to various stimuli were the following: ITT: 5.3; ARG: 2.9; CLO: 1.5; GLU: 7.6; PD: 2.2; GAL: 4.0; GHRH: 5.0; GHRH+ARG: 17.8; GHRH+PD: 17.9; HEX: 21.6; GHRH+HEX: 57.1. These results confirm that, among classical provocative tests of GH secretion, ITT followed by ARG and GLU are the most potent ones and possess clear limits of normality. GHRH+ARG or PD and HEX are strong stimuli of GH secretion which, however, is maximally stimulated by a combination of GHRH and a low dose of HEX. It is recommended that each test is used with appropriate cut-off limits.     

The diagnosis of growth hormone deficiency (GHD) in successfully treated acromegalic patients

Due to persistent qualitative abnormalities in GH secretion following treatment, and lack of a sensitive marker of GHD in mid-adult life it is extremely difficult to diagnose GHD in treated acromegalic patients. The diagnosis of GHD in patients with pituitary disease relies on provocative tests of GH reserve. Arginine releases GH by reducing somatostatin inhibition of GH release, whereas GH secretagogues (GHS) affect GH release by direct stimulation of the GHS receptor, though an intact GH releasing hormone (GHRH) axis is a prerequisite. The peak GH response to insulin-induced hypoglycaemia and arginine in acromegalic patients, in whom basal serum GH levels of less than 5 mU/l have been achieved, is greatly diminished in those treated by hypothalamo-pituitary irradiation. We aimed to study the response of successfully treated acromegalic patients to the growth hormone secretagogue hexarelin in view of its different putative mechanism of action, and in addition, to determine whether it has any value in the diagnosis of GH deficiency in this subset of patients. Nineteen acromegalic patients, in whom mean serum GH levels below 5 mU/l have been achieved through treatment, were recruited. Eight of the patients had been treated by surgery alone (Group A) and 11 had received primary or postoperative irradiation (Group B). All patients underwent 20 min blood sampling to provide a 24-h GH profile. Serum IGF-I was measured from a sample drawn between 0900 h and 1000 h. On a second visit arginine 20 g/m2 was infused over 30 min, blood samples were taken before commencing the infusion and at 30-min intervals thereafter for 180 min. At the final visit hexarelin 1.5 mcg/kg was administered as an intravenous bolus at t = 0. Blood was drawn at 15-min intervals from - 30 to 180 min. All patients in group A showed an increment in serum GH following hexarelin (DeltaGHHEX) > 20 mU/l, a normal response to arginine, and a mean 24-h GH > 0.5 mU/l. In group B only 4/11 achieved a DeltaGHHEX > 20 mU/l, 5/11 producing a response of < 2 mU/l. Four of the five patients with a DeltaGHHEX < 2 mU/l were also demonstrated to have a mean 24-h GH of < 0.5 mU/l and serum IGF-I SDS < + 0.5. All four patients in Group B who achieved a DeltaGHHEX > 20 mU/l, were observed to show an absent or minimal GH response to arginine. Despite loss of the GH response to arginine, the DeltaGHHEX is retained in a proportion of those patients in whom "safe" GH levels were achieved following irradiation. From the putative mechanisms of action of these provocative agents a plausible explanation would be that the GHRH axis is more resilient than endogenous somatostatin-secreting neurones to radiation-induced damage. Furthermore, GH secretagogues may have a role, in combination with serum IGF-I levels, in the diagnosis of GH deficiency in treated acromegaly.     

HYPOTHALAMIC GROWTH HORMONE RELEASING FACTOR DEFICIENCY FOLLOWING CRANIAL IRRADIATION

The effect of synthetic human pancreatic tumour GH releasing factor (hp GRF1–44) on GH release has been studied in 10 patients with radiation-induced GH deficiency and four normal subjects. All 10 patients showed subnormal GH responses to both an ITT (median peak GH 3.2 mU/l) and to arginine stimulation (median peak GH 2.9 mU/l), although the remainder of pituitary function was intact. Following an acute intravenous bolus (100 /μg) of hp GRF1-44, there was no GH response in two patients and a subnormal but definite GH response in a further four. The remaining four patients showed a significant GH response (median peak GH level 29 mU/l; range 22–57 mU/l) to hp GRF1-44, similar in magnitude and timing to that seen in the four normals. This strongly suggests that in these four subjects, the discrepancy in GH responses to hp GRF1-44, ITT and to arginine was a result of radiation-induced hypothalamic damage leading to a deficiency of endogenous GRF. The availability of synthetic hp GRF capable of stimulating GH secretion means that the distinction between hypothalamic and pituitary causes of GH deficiency will be of considerable therapeutic importance in the future.     

Postoperative persistent thyrotrophin releasing hormone-induced growth hormone release predicts recurrence in patients with acromegaly

OBJECTIVE: To assess the predictive value of postoperative thyrotrophin releasing hormone (TRH)-induced GH responsiveness in relation to (late) postoperative outcome in patients in remission after surgery for acromegaly. PATIENTS: and methods One hundred and twenty-nine patients underwent surgery for acromegaly in our institution between 1977 and 1996. TRH tests and oral glucose tolerance tests (GTT) were performed and serum IGF-I concentrations were measured pre- and postoperatively and during follow-up. Criteria for postoperative remission were a mean serum GH concentration < 5 mU/l and/or serum GH after an oral glucose tolerance test < 1 mU/l immunofluorometric assay (IFMA) or < 2.5 mU/l (radioimmunosassay), together with a normal serum IGF-I concentration. RESULTS: Preoperatively, the TRH-induced GH response was highly variable, with gradual overlap between 'nonresponders' and 'responders'. Arbitrarily defined as a doubling of serum GH concentration, 45.6% of patients were 'responders' to TRH. GH response after TRH injection was significantly correlated to the TRH-induced prolactin response but not to preoperative GH concentration or adenoma size. After surgery, remission was achieved in 83 of the 129 patients. Postoperative remission was significantly correlated to mean preoperative serum GH concentration and preoperative glucose-suppressed serum GH but not to tumour class. Seventy-one patients with early postoperative remission were followed without adjuvant treatment for a mean of 9.4 +/- 0.7 years (range 0-23 years). Forty-one of these patients were TRH responsive as defined by at least doubling of the serum GH concentration preoperatively. Of the 71 patients, 12 developed recurrence of disease, as defined by insufficient GH suppression during oral GTT, and elevated IGF-I and mean serum GH concentration. Irrespective of the preoperative response to TRH, the initial postoperative TRH test was predictive of developing disease recurrence with a sensitivity of 75% and a specificity of 100% when an absolute GH increase of 3.75 mU/l was chosen to define paradoxical responsiveness. A stimulated GH 1.6 times basal was predictive of recurrence with a sensitivity of 83% and a specificity of 73%, and 2.1 times basal was predictive with a sensitivity of 75% and a specificity of 80%. None of the 32 patients with postoperative normalization of the preoperatively present TRH-induced GH response, defined as a postoperative GH increase < 3.75 mU/l, developed recurrence of disease, while all nine patients with a GH increase above this level developed recurrence of acromegaly. CONCLUSION: To our knowledge this is the first report which addresses the value of early postoperative TRH-induced GH responsiveness in predicting late surgical outcome using receiver-operating characteristic (ROC) curves to redefine a postoperative paradoxical response instead of arbitrarily chosen criteria. An absolute postoperative GH response of more than 3.75 mU/l was associated with recurrence in all nine patients, while all 32 patients with normalization of previously paradoxical response are still in remission. Our findings from this study demonstrate that the TRH test is a valuable tool in the early identification of patients at risk of developing postoperative recurrence of acromegaly.     

Diagnosis of growth hormone (GH) deficiency in adults with hypothalamic-pituitary disorders: comparison of test results using pyridostigmine plus GH-releasing hormone (GHRH), clonidine plus GHRH, and insulin-induced hypoglycemia as GH secretagogues

The insulin tolerance test (ITT) is widely accepted as the method of choice to evaluate GH secretion capacity in adults with hypothalamic-pituitary disorders. However, the test is not suitable in the elderly or in patients with cardiovascular disease or seizure disorders. In recent years alternatives to the ITT have been introduced. The purpose of the present study was to investigate the diagnostic outcome with the ITT, the pyridostigmine plus GHRH (PD + GHRH) test, the clonidine plus GHRH (CLO+GHRH) test, and insulin-like growth factor I (IGF-I) in an unselected group of patients with hypothalamic-pituitary disease. An evaluation of the reproducibility of the different stimulation tests was included in the study. Based on repeated testing with the various GH stimulation tests in healthy adult males and females, the lower limits of normality for the ITT, the PD+GHRH test, and the CLO+GHRH test were 3.92, 12.8, and 19.0, microg/L, respectively. A consecutive group of 26 unselected patients with hypothalamic-pituitary disorders, 13 males and 13 females (median age, 44 ys), were tested twice with all stimulation tests, except that only 10 patients were tested once with the CLO+GHRH test due to side-effects related to clonidine. The peak GH responses between test 1 and test 2 correlated significantly in both the ITT and the PD + GHRH test (P < 0.02), and no significant difference was observed in the median peak response to repeated testing. In addition, no sex difference was observed. The coefficients of variation (CV) were 96% (ITT) and 45% (PD + GHRH), but in the majority of patients low values were repeatedly low. The peak GH response was significantly higher during the PD+GHRH test than during the ITT (P = 0.008). In the 10 patients tested with the PD+GHRH and CLO+GHRH tests there was no significant difference in the peak GH response (P = 0.398). When the test specific cut-off values were used, no significant difference in diagnostic outcome was observed between the various tests (P > 0.3). In contrast, the diagnosis obtained with IGF-I differed significantly from all GH stimulation tests (P < 0.03). Twenty (77%) and 22 (85%) patients were diagnosed to be GH deficient with the ITT and the PD+GHRH test, respectively. Of the 14 patients with multiple pituitary failure (>2 hormones affected), GH deficiency was present in more than 90% regardless of the type of stimulation test used. The IGF-I levels were only subnormal in 42% of the patients and did not correlate with the peak GH responses in any of the stimulation tests (P > 0.05). Except for 1 patient all patients with subnormal IGF-I were GH deficient in all stimulation tests. It is concluded that in patients with hypothalamic-pituitary disease and a normal IGF-I level 2 stimulation tests should be performed to establish a diagnosis of GH deficiency. In patients with a subnormal IGF-I value a single GH stimulation test should be sufficient to confirm the presence of GH deficiency.     

IMPAIRED GROWTH HORMONE RESPONSE TO INSULIN-INDUCED HYPOGLYCAEMIA IN OBESE PATIENTS: RESTORATION BLOCKED BY RITANSERIN AFTER FENFLURAMINE ADMINISTRATION

The aim of the present study was to test whether the serotoninergic system may be involved in the well known reduced growth hormone (GH) response to insulin-induced hypoglycaemia (IIH) in obese patients. Ten obese women and 10 normal-weight control women underwent three IIH tests, at 14-day intervals: the first in basal conditions, the other two after randomized administration of a serotoninergic drug, fenfluramine (FF, 120 mg/day for 7 days) and FF plus ritanserin (RIT, 30 mg/day for the first 2 days and 20 mg/day on the following days). Ritanserin is a new selective 5-HT2 blocker receptor agent. Both controls and obese patients showed similar normal basal GH levels before each test and insulin administration always effectively reduced glucose levels to values lower than 2.2 mmol/l. In the controls, the expected GH increase to IIH (peak value 56 +/- 13.4 mU/l, AUC 234.4 +/- 55 mU/min/ml) was unaffected by FF administration (peak value 43 +/- 11.4; AUC 216.8 +/- 34.8). In response to the first IIH, the obese patients showed a significantly lower GH increase than in the case of the controls (peak value 21.4 +/- 4.6 mU/l, P less than 0.02; AUC 93.2 +/- 18.6, P less than 0.02). However, in comparison with the basal test, FF administration significantly (P less than 0.001) enhanced GH response to insulin hypoglycaemia (peak value 33.4 +/- 4; AUC 150 +/- 14.6), reaching values not significantly different from those of the controls.(ABSTRACT TRUNCATED AT 250 WORDS)