Pulsatile secretion pattern of growth hormone in turkeys: Effects of age and sex

Male and female turkeys were cannulated through the jugular vein, and blood samples were withdrawn remotely at 10-min intervals for a period of 8 hr at two points in the posthatch growth phase (4 and 14 weeks of age). Growth hormone (GH) concentration was determined for each sample by radioimmunoassay using a recombinant chicken growth hormone preparation as standard. Data were evaluated for age- and sex-related differences. Four-week-old male and female turkeys displayed a pulsatile pattern of GH secretion. Growth hormone secretory profile characteristics differed significantly between ages with regard to overall mean, number of peaks, amplitude of peaks, interval between peaks, baseline, and total GH detected. Male four-week-old turkeys had a peak amplitude significantly greater than that of females of the same age. Older (14-week-old) male turkeys demonstrated a significantly greater nunber of GH secretory peaks than females during the 8-hr sampling period; however, overall it did not appear that the older birds had an organized pattern of GH secretion above baseline levels.     

Plasma growth hormone response to growth hormone-releasing factor in acromegalic patients

Synthetic growth hormone-releasing factor (hpGRF-44) (100 micrograms) was administered intravenously to ten acromegalic patients. The time when the peak of plasma GH occurred as well as the magnitude of the response were highly variable among these ten patients. From the GH response patterns the ten acromegalic patients were tentatively classified into three groups: (1) those highly GRF-dependent whose GH level increased to four times basal, (2) those moderately GRF-dependent whose GH level rose to less than two times basal and (3) those GRF-resistant whose GH level did not change. These data suggest that there may be differences in the GRF-receptor system in pituitary adenomas causing acromegaly.     

Sleep-related growth hormone release following 2-bromo-alpha-ergocriptine treatment in acromegalic patients

Plasma growth hormone (GH) concentrations were measured over 24 h in seven acromegalic patients before and during treatment with 2-bromo-alpha-ergocriptine (CB-154). Before treatment basal plasma GH levels were consistently elevated but no significant change was observed between the mean plasma GH levels during sleep and during waking in five of the seven patients examined. The daily administration of CB-154 (5 to 10 mg, orally) for 14 days resulted in a significant fall in the 24 h mean plasma GH levels in six of the seven patients. In all of the six patients who responded to CB-154 treatment, the mean plasma GH concentrations during sleep were significantly greater than during waking. Daytime sleep was associated with a significant rise in plasma GH in both of the two patients examined. It is concluded that CB-154 treatment resulted in a significant decrease in plasma GH levels with sleep-related increase in some acromegalics although the mechanism responsible for this sleep-related GH rise remains to be further investigated.     

Placental and pituitary growth hormone secretion during pregnancy in acromegalic women

It is now well established that during the second half of normal pregnancy, the human placenta secretes its specific GH variant (placental GH) in increasing amounts up to delivery. During the same period, pituitary GH secretion is progressively suppressed. The present study was aimed at clarifying the physiology of GH secretion in pregnant acromegalic women. Two young women remained acromegalic despite transphenoidal removal of their pituitary adenoma. Increased basal levels of GH and insulin-like growth factor-I (IGF-I) as well as paradoxical GH release after TRH injection were noted. Both women became pregnant and delivered term babies without any complication. In both patients, pituitary GH remained elevated during the entire pregnancy, contrary to the situation in normal women. Paradoxical GH release after TRH treatment was also present, whereas no response was observed in five normal control subjects. GH pulsatility studies revealed a highly pulsatile secretory pattern of pituitary GH, in contrast to that in normal woman, whose placental GH is secreted tonically. Tissue placental GH concentrations were within the range of levels in normal placentas. An increase in serum IGF-I in late pregnancy was also similar to that observed in normal pregnancy. These findings confirm that increased IGF-I levels are not pituitary GH dependent in late pregnancy. They add new evidence that adenomatous somatotrophs lack an IGF-I-dependent feedback regulation present in normal somatotrophs.     

Octreotide long-acting repeatable and lanreotide Autogel are equally effective in controlling growth hormone secretion in acromegalic patients

OBJECTIVE: Recently a new depot preparation of the long-acting somatostatin analogue, lanreotide Autogel was introduced for the treatment of acromegaly. Like octreotide long-acting repeatable (LAR), it has high binding affinity for the somatostatin receptor subtype SSTR 2 and less binding affinity for SSTR 5. We hypothesized that the ability to suppress growth hormone (GH) secretion in patients with acromegaly would be similar for these depot preparations. PATIENTS AND STUDY DESIGN: Seven patients (mean age+/-S.E.M. 48.4+/-7 years) on long-term octreotide LAR treatment at a monthly injection interval for a mean of 2.8 years were enrolled in the study. They underwent a GH secretory profile study with 10 min sampling for 24 h, 28 days after an injection. At 2, 4 and 6 weeks after the next injection fasting GH profiles (every 30 min for 3.5 h) and serum IGF-I measurements were measured. These investigations were repeated 12 months later, when the patients were on an individually titrated stable dose of lanreotide Autogel. RESULTS: Secretory characteristics and total 24 h GH secretion, estimated by deconvolution analysis of the 10 min 24 h plasma GH concentrations, did not show differences between these two long-acting somatostatin analogues. Both drugs were equally effective in GH and IGF-I suppression as measured at 2, 4 and also at 6 weeks following an injection. CONCLUSION: The efficacy of lanreotide Autogel and octreotide LAR was equal, notwithstanding that these drugs are administered in a different way and have different pharmacokinetics.     

Induction of growth hormone and prolactin secretion by luteinizing hormone-releasing hormone and its blockade by bromoergocriptine in acromegalic patients.

In an attempt to evaluate the effect of LRH on GH and PRL secretion, LRH in a dose of 100 micrograms was injected iv to 22 patients with active acromegaly. A definite increase in both serum GH and PRL levels was observed in one patient, while four other subjects responded to LRH to secret either GH or PRL. The effectiveness of LRH on GH and PRL release was not correlated with the age or sex of patients, the basal levels of serum GH or PRL, the GH response to TRH administration, or the increase in serum gonadotropin concentrations after LRH injection. In three patients, this LRH-induced GH and PRL release was completely blocked by pretreatment with 2-bromo-alpha-ergocriptine (CB154). The results suggest that elevations of GH and PRL after LRH occur rather sporadically in acromegalic patients and that the action of LRH on GH release is occasioned by a different mechanism from that of TRH.     

The influence of diabetes mellitus on thyrotropin response to thyrotropin-releasing hormone in untreated acromegalic patients

Impairment of thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) has been documented in patients with uncontrolled diabetes mellitus (DM). In acromegalic patients, however, there have been no data regarding TSH secretion studied taking the existence of DM into consideration. Therefore, we investigated the TSH response to TRH [expressed as TSH increment (delta TSH)] in 14 untreated acromegalic patients, who did not show the suprasellar extension of adenoma, divided into two groups on the basis of either presence or absence of uncontrolled DM, and in 28 normal subjects. The mean max delta TSH was significantly reduced (p less than 0.02) in acromegalic patients despite similar mean serum T4 and free T4 index (FT4l) levels. Furthermore, the mean basal and max delta TSH in 7 patients with DM (FBS, 120-300 mg/dl; HbA1, 8.8-15.2%) were significantly lower than those in 7 patients without DM (p less than 0.05 and p less than 0.02, respectively) despite similar the mean serum T3, T4, FT4l, growth hormone (GH) and prolactin (PRL) levels and sellar volume. In 4 patients with DM the TSH response to TRH 6-8 weeks after insulin therapy, when their HbA1 levels were normal, increased compared to that before insulin therapy. The mean max delta TSH after selective adenomectomy in 8 patients (3 in DM group and 5 in non-DM group), whose fasting basal GH fell to less than 5 ng/ml, was almost identical to that in normal subjects. In conclusion, the present study suggests that the abnormality in TSH secretion in acromegalic patients may be increased by the existence of uncontrolled DM.     

Effects of sex and age on growth hormone response to growth hormone-releasing hormone in healthy individuals

The influence of age and sex on human GH secretion is controversial. In previous studies, serum GH responses to arginine and insulin-induced hypoglycemia were significantly higher in pre- and postovulatory women than in men. In contrast, recent studies suggest that GH responsiveness to GHRH is higher in normal young men than in age-matched women. To clarify the question of sex and age influence on GHRH-(1-44)-stimulated GH secretion, we studied 116 normal women and men (with body mass indexes of 18-25 and 19-26, respectively) between the ages of 18 and 95 yr. The peak serum GH increments after GHRH administration were significantly higher in premenopausal women than in age-matched men (P less than 0.003 for the age group 18-30 yr and P less than 0.03 for the age group 30-50 yr, as assessed by analysis of variance). The responses were not different in postmenopausal women and age-matched men. Multiple regression analysis revealed a significant negative correlation between GHRH-induced GH responses (integrated area under the curve) and age in both women (P less than 0.002) and men (P less than 0.001). In addition, we determined basal serum testosterone, estradiol, cortisol, and PRL levels in all subjects. Multivariate regression analysis of the GH responses to GHRH administration revealed a significant positive correlation (P less than 0.01) between serum estradiol and both GH increase and the area under the GH response curve. No correlation was found between GHRH-stimulated GH secretion and basal serum cortisol, testosterone, or PRL concentrations. Our data clearly demonstrate a marked influence of both sex and age on GHRH-stimulated GH secretion. We found a higher GH increase in premenopausal women compared with age matched-men and an age-dependent decrease in GHRH-stimulated GH secretion in both sexes. Furthermore, in women a significant influence of estradiol on GH secretion after GHRH administration could be demonstrated.     

Evaluation of growth hormone stimulation tests in cured acromegalic patients

We have evaluated the GH peak response to insulin tolerance test (ITT) and to GHRH + arginine in 11 patients cured of acromegaly after treatment with surgery/radiotherapy and compared them to a control group matched for age and sex. GH peak response was significantly higher in the control group than in the patient group (11.21 ± 6.98 vs. 4.46 ± 6.90 ng/ml, p=0.010). Seven patients had a GH peak response of less than 3 ng/ml, compatible with the diagnosis of GH deficiency. Peak GH response after GHRH + arginine was significantly lower in the group of patients with GH peak of less than 3 ng/ml during ITT as compared to the group with GH peak of more than 3 ng/ml, and in all cases the diagnosis of GH deficiency was confirmed. Mean IGF-I level was not different between the patients and controls, as well as between patients with and without GH deficiency diagnosed by the stimulation tests. Conclusion: The incidence of GHD diagnosed by stimulation tests is high in patients cured of acromegaly.     

Influence of L-prolyl-L-leucyl-glycine amide on growth hormone secretion in normal and acromegalic subjects.

Melanocyte Release-Inhibiting Peptide (MRIP-I) did not affect circulating levels of ACTH, LH, FSH, TSH,ORL, betaMSH and insulin when iv infused (5.0 mg in 5 min plus 0.4 mg/min for 70-115 min), while it significantly reduced serum GH response to hypoglycemia in normal subjects and lowered serum GH levels in acromegalics. There was no correlation between the fall in serum GH after MRIP and after dopaminergic drugs in acromegaly. These data are compatible with either a direct suppressive action exerted by MRIP-I at pituitary level or an extra-pituitary effect not involving dopaminergic pathways. It can be spec-lated that since labelled MRIP-I accumualtes in the pineal and melatonin blunts GH response to hypoglycemia, the pineal gland might be involved in the MRIP-I-induced suppression of GH secretion.     

The somatostatin analog SMS 201-995 induces long-acting inhibition of growth hormone secretion without rebound hypersecretion in acromegalic patients

The acute effect of the somatostatin analog SMS 201-995 (SMS) was investigated in eight acromegalic patients. This substance is an octapeptide [DPhe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-(ol)] that inhibits GH release in experimental animals and man. After a control day, 50 micrograms SMS were injected sc, and plasma GH and insulin and blood glucose levels were measured at multiple intervals for 24 h. GH significantly (P less than 0.001) decreased in seven of eight acromegalic patients from 30 +/- 5 (+/- SE) to an average of 10.7 +/- 4 micrograms/l from 1-10 h after drug administration. No rebound effect occurred. Postprandial blood glucose levels were significantly (P less than 0.01) higher between 2 and 4 h after SMS treatment compared with control day values, and there was a substantial reduction in insulin secretion, as estimated by the area under the curve (P less than 0.01), during the first 3 h after SMS administration. Circulating GH was not altered by SMS or the dopamine agonist mesulergine in one patient, but the combination of both substances (50 micrograms SMS, sc, and 0.5 mg mesulergine, orally) reduced GH to below 50% of basal. In vitro studies showed that 1 PM, 0.1 nM, and 10 nM SMS or natural somatostatin exerted a similar inhibitory effect (12-39% reduction; P less than 0.01 for all three strengths) on GH release by cultured human pituitary tumor cells. In conclusion, the somatostatin derivative SMS exerts a potent and prolonged inhibitory action on GH secretion and a shorter lasting suppression of insulin in acromegalic patients. Therefore, it may represent a useful tool in the chronic management of this condition.     

The assay of urinary growth hormone in normal and acromegalic adults

OBJECTIVES: To establish a normal range for urinary growth hormone in adults and to investigate the urinary growth hormone levels in patients with acromegaly, comparing these with the serum growth hormone results of a glucose tolerance test. We also studied the molecular identity of the growth hormone recognized by our assay method. DESIGN: Overnight urine samples and, in some cases, timed urine samples taken during the day were obtained from healthy volunteers and acromegalic patients. A standard glucose tolerance test with serum growth hormone measurements was performed on the acromegalic patients. PATIENTS: One hundred and thirty-five normal adults and 33 acromegalic patients were studied. MEASUREMENTS: Urinary growth hormone was measured using a sensitive and precise assay developed previously. RESULTS: In healthy volunteers overnight urinary growth hormone values fell gradually with increasing age, but there was no significant difference between men and women in any decade or between smokers and non-smokers. Sexual intercourse had no detectable effect on the values, but there was a large increase following strenuous exercise. Studies of the diurnal patterns in normal and abnormal adults suggested that it might be possible to diagnose acromegaly on a random urine sample. Gel filtration studies on a urine sample from an acromegalic patient showed a single peak of molecular weight 22,000. Using overnight collections there was clear discrimination between the values given by the normal adults and the acromegalic patients and an excellent correlation between urinary growth hormone levels in acromegalic patients and the mean serum growth hormone in a glucose tolerance test. CONCLUSIONS: In contrast to some other groups we conclude that urinary growth hormone provides a useful, non-invasive screening test for acromegaly, but this conclusion depends crucially on the assay being sensitive and precise at low values.     

Bioactivity and heterogeneity of human growth hormone in urine from acromegalic patients

Bioactivity of hGH in urine from five acromegalic patients was determined by Nb2 rat lymphoma bioassay (Nb2BA) and IM-9 receptor modulation assay (RMA). One urine sample (case 1) was concentrated by dialysis and lyophilization. Bioactivity by IM-9 RMA showed close correlations with immunoactivity by RIA in serial dilutions (RMA/RIA; 0.66-1.77). The estimates of bioactivity by Nb2BA were higher in all diluted samples except undiluted one than those of immunoactivity. Four samples were concentrated by affinity chromatography, dialysis and lyophilization. The ratio of RMA and RIA estimates was between 0.81-1.24, and that of Nb2BA and RIA estimates was between 0.46-2.62. Heterogeneity of urinary hGH was analyzed by gelfiltration using TSK-G-3000SW column by high performance liquid chromatography (HPLC) and by sensitive sandwich enzyme immunoassay. In addition to the main peak of 22K molecular weight (more than 97%), very small peaks of 40-60K (big hGH) and 150K (big-big hGH) were detected in chromatographic profile. Urinary hGH from acromegalic patients was bioactive in IM-9 RMA and Nb2BA. The predominant form of urinary hGH from acromegalic patients was little hGH, but big and big-big hGH were detected by sensitive sandwich enzyme immunoassay.     

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.     

Different responses of growth hormone secretion to guanfacine, bromocriptine, and thyrotropin-releasing hormone in acromegalic patients with pure growth hormone (GH)-containing and mixed GH/prolactin-containing pituitary adenomas

There is great variability in the GH secretory responses to different stimuli in patients with acromegaly. In the present study, we compared the effects on GH secretion of two compounds (bromocriptine and TRH), which presumably act directly at the pituitary level, with the effect of the centrally acting alpha-adrenergic agonist guanfacine in 14 untreated acromegalic patients. These in vivo responses of GH release were correlated with the results of immunocytochemical studies of the pituitary adenomas. In nine patients with pure GH-containing adenomas, GH secretion was suppressed by bromocriptine by more than 50% in one patient, while TRH stimulated GH release by more than 100% in another patient. Guanfacine (2 mg, orally) did not elicit a change in circulating GH levels in any of these nine patients. In the group of five patients with mixed GH/PRL-containing adenomas, however, bromocriptine suppressed GH levels by more than 50% in all patients, and TRH stimulated GH release by more than 100% in four of them. Guanfacine stimulated GH secretion significantly in four of these five patients. Guanfacine inhibited GH secretion significantly in five other acromegalic patients who had been treated 5-10 yr previously by external pituitary irradiation. We conclude that in acromegaly, the presence of PRL within the GH-secreting pituitary adenoma makes GH secretion more sensitive to bromocriptine and TRH, while normal sensitivity to hypothalamus-mediated stimulation (alpha-adrenergic agonist) is retained to some extent. In contrast, pure GH-secreting tumors responded little or not at all to bromocriptine, TRH, or guanfacine.     

Effect of vasoactive intestinal polypeptide on growth hormone secretion in perifused acromegalic pituitary adenoma tissues

The effects of vasoactive intestinal polypeptide (VIP), dopamine, and somatostatin (SRIF) on GH secretion were examined in vitro in perifused pituitary adenoma tissues obtained at surgery from seven patients with acromegaly. The perifusion of VIP at 5 x 10(-8) M resulted in a significant increase in effluent GH levels in five of the seven adenomas. A dose-related GH response was observed from 5 x 10(-9) to 5 x 10(-7) M VIP in two adenomas examined. SRIF at 5 x 10(-8) to 10(-7) M suppressed not only baseline secretion of GH but also inhibited GH rises elicited by VIP in six of the seven adenomas. Dopamine at 5 x 10(-7) to 5 x 10(-6) M decreased the baseline secretion of GH in six of the seven adenomas. In four of the six adenomas responsive to dopamine, dopamine suppressed VIP-induced GH release when perifused simultaneously. In the remaining two dopamine-sensitive adenomas in which VIP alone failed to affect GH release, the inhibition by dopamine of GH release was blocked by VIP perifused concomitantly with dopamine. Synthetic TRH or theophylline perifused at the end of the experiment stimulated GH release in all of the adenomas, indicating the viability of tumor cells throughout the study. These results suggest that VIP stimulates GH release by its direct action on pituitary adenoma cells of acromegalic patients and that VIP, SRIF, and dopamine interact at the pituitary level in modulating GH secretion from these adenomas.     

Effects of acute infusion of erythropoietin on paradoxical responses of growth hormone to thyrotropin-releasing hormone in acromegalic patients

OBJECTIVE: Our aim has been to evaluate the effects of i.v. infusion of recombinant human erythropoietin (rhEPO) on the responses of growth hormone (GH), prolactin (PRL) and thyrotropin (TSH) to thyrotropin-releasing hormone (TRH) stimulation in acromegalic patients. METHODS: We studied 16 patients (8 females, aged 29-68 years) with active acromegaly and 12 control subjects (7 females, 24-65 years). All participants were tested with TRH (400 microg i.v. as bolus) and with TRH plus rhEPO (40 U/kg at a constant infusion rate for 30 min, starting 15 min before TRH injection) on different days. Blood samples were obtained between -30 and 120 min for GH and PRL determinations, and between -30 and 90 min for TSH determinations. Hormone responses were studied by a time-averaged (area under the secretory curve (AUC)) and time-independent (peak values) analysis. RESULTS: Twelve patients exhibited a paradoxical GH reaction after TRH administration with great interindividual variability in GH levels. When patients were stimulated with rhEPO plus TRH there were no changes in the variability of GH responses or in the peak and AUC for GH secretion. Infusion with rhEPO did not induce any significant change in GH secretion in normal subjects. Baseline and TRH-stimulated PRL concentrations in patients did not differ from those values found in controls. When TRH was injected during the rhEPO infusion, a significant (P<0.05) increase in PRL concentrations at 15-120 min was found in acromegalic patients. Accordingly, the PRL peak and the AUC for PRL secretion were significantly increased in patients. Infusion with rhEPO had no effect on TRH-induced PRL release in control subjects. Baseline TSH concentrations, as well as the TSH peak and the AUC after TRH, were significantly lower in patients than in controls. Infusion with rhEPO modified neither the peak TSH reached nor the AUC for TSH secretion after TRH injection in acromegalic patients and in healthy volunteers. CONCLUSION: Results in patients with acromegaly suggest that (i) the paradoxical GH response to TRH is not modified by rhEPO infusion, (ii) rhEPO has no effect on TRH-induced TSH release, and (iii) acute rhEPO administration increases the TRH-induced PRL release in acromegalic patients.