Ghrelin and GHRP-6-induced ACTH and cortisol release in thyrotoxicosis

Thyrotoxicosis might alter the hypothalamic-pituitary-adrenal (HPA) axis. We evaluated the effects of ghrelin and GHRP-6 on the HPA axis in 20 hyperthyroid patients and in 9 controls. Mean basal cortisol (μg/dl) and ACTH (pg/ml) levels were higher in hyperthyroidism (cortisol: 10.7 ± 0.7; ACTH: 21.5 ± 2.9) compared to controls (cortisol: 8.1 ± 0.7; ACTH: 13.5 ± 1.8). In thyrotoxicosis ∆ AUC cortisol values (μg/dl.90 min) after ghrelin (484 ± 80) and GHRP-6 (115 ± 63) were similar to controls (ghrelin: 524 ± 107; GHRP-6: 192 ± 73). A significant increase in ∆ AUC ACTH (pg/ml.90 min) after ghrelin was observed in thyrotoxicosis (4,189 ± 1,202) compared to controls (1,499 ± 338). ∆ AUC ACTH values after GHRP-6 were also higher, although not significantly (patients: 927 ± 330; controls: 539 ± 237). In summary, our results suggest that ghrelin-mediated pathways of ACTH release might be activated by thyroid hormone excess, but adrenocortical reserve is maintained.     

Growth hormone responses to GH-releasing peptide (GHRP-6) in hypothyroidism

OBJECTIVE Both spontaneous and stimulated GH secretion are reduced in patients with hypothyroidism. The mechanisms involved in these alterations are not yet fully understood. GHRP-6 is a synthetic hexapeptide that releases GH both in vivo and in vitro. Its mechanism of action is unknown, but there is evidence that this peptide acts as a functional somatostatin antagonist at pituitary level. The aim of this study was to evaluate the GH response to GHRP-6 in patients with primary hypothyroidism and in normal controls. DESIGN Patients with hypothyroidism and normal controls were randomly submitted to 3 tests with GHRH (100 μg i.v.), GHRP-6 (1 μg/kg i.v.) and GHRH + GHRP-6, on separate days. PATIENTS Eleven patients with primary hypothyroidism were compared with 10 control subjects. MEASUREMENTS GH, TSH and free T4 were measured by immunofluorometric assay and IGF-I by radioimmunoassay. RESULTS Hypothyroid patients had markedly lower peak GH values (mean ± SE μg/l) after GHRH administration (4.1 ± 0.9) compared to control subjects (24.9 ± 5.1). After GHRP-6 injection hypothyroid patients had a significantly higher GH release (12.6 ± 1.9) than that obtained with GHRH, while in control subjects GH values were similar (22.1 ± 3.6). No significant differences in peak GH responses were observed following the administration of either GHRP-6 alone (controls 22.1 ± 3.6; patients 12.6 ± 1.9) or in combination with GHRH (controls 77.4 ± 15.0; patients 52.8 ± 10.9), despite the trend to smaller responses in hypothyroid patients. CONCLUSION We have shown that patients with primary hypothyroidism have higher GH responses to GHRP-6 than to GHRH, which are markedly blunted. When GHRP-6 was associated with GHRH, a significant increase in the GH response was observed in these patients, which could suggest a role for somatostatin in this process. Our data suggest that thyroid hormones modulate GH release induced by GHRH and GHRP-6 through different mechanisms. However, additional studies are necessary to further elucidate this hypothesis.     

Decreased ghrelin-induced GH release in thyrotoxicosis: comparison with GH-releasing peptide-6 (GHRP-6) and GHRH

In thyrotoxicosis GH response to several stimuli is impaired, but there is no data on ghrelin-induced GH release in these patients. Ghrelin is a potent GH secretagogue and it also increases glucose levels in men. The aim of this study was to evaluate the effects of ghrelin (1 μg/kg), GHRP-6 (1 μg/kg) and GHRH (100 μg), i.v., on GH levels in 10 hyperthyroid patients and in 8 controls. Glucose levels were also measured during ghrelin and GHRP-6 administration. In control subjects and hyperthyroid patients peak GH (μg/l; mean ± SE) values after ghrelin injection (controls: 66.7 ± 13.6; hyper: 19.3 ± 2.4) were significantly higher than those obtained after GHRP-6 (controls: 26.7 ± 5.1; hyper: 12.6 ± 1.3) and GHRH (controls: 13.5 ± 4.3; hyper: 5.3 ± 1.3). There was a significant decrease in GH responsiveness to ghrelin, GHRP-6 and GHRH in the hyperthyroid group compared to controls. In control subjects and hyperthyroid patients basal glucose (mmol/l) values were 4.5 ± 0.1 and 4.7 ± 0.2, respectively. There was a significant increase in glucose levels 30 min after ghrelin injection (controls: 4.9 ± 0.1; hyper: 5.2 ± 0.2), which remained elevated up to 120 min. When the two groups were compared no differences in glucose values were observed. GHRP-6 administration was not able to increase glucose levels in both groups. Our data shows that GH release after ghrelin, GHRP-6 and GHRH administration is decreased in thyrotoxicosis. This suggests that thyroid hormone excess interferes with GH-releasing pathways activated by these peptides. Our results also suggest that ghrelin’s ability to increase glucose levels is not altered in thyrotoxicosis.     

Adrenocorticotrophic hormone (ACTH) responsiveness to ghrelin increases after 6 months of ketoconazole use in patients with Cushing's disease: comparison with GH-releasing peptide-6 (GHRP-6)

Background In Cushing’s disease (CD), adrenocorticotrophic hormone (ACTH)/cortisol responses to growth hormone secretagogues (GHS), such as ghrelin and GHRP‐6, are exaggerated. The effect of clinical treatment of hypercortisolism with ketoconazole on ACTH secretion in CD is controversial. There are no studies evaluating ACTH/cortisol responses to GHS after prolonged ketoconazole use in these patients. Objective To compare ghrelin‐ and GHRP‐6‐induced ACTH/cortisol release before and after ketoconazole treatment in patients with CD. Design/patients Eight untreated patients with CD (BMI: 28·5 ± 0·8 kg/m²) were evaluated before and after 3 and 6 months of ketoconazole treatment and compared with 11 controls (BMI: 25·0 ± 0·8). Results After ketoconazole use, mean urinary free cortisol values decreased significantly (before: 613·6 ± 95·2 nmol/24 h; 3rd month: 170·0 ± 27·9; 6th month: 107·9 ± 30·1). The same was observed with basal serum cortisol (before: 612·5 ± 69·0 nmol/l; 3rd month: 463·5 ± 44·1; 6th month: 402·8 ± 44·1) and ghrelin‐ and GHRP‐6‐stimulated peak cortisol levels (before: 1183·6 ± 137·9 and 1045·7 ± 132·4; 3rd month: 637·3 ± 69·0 and 767·0 ± 91·0; 6th month: 689·8 ± 74·5 and 571·1 ± 71·7 respectively). An increase in basal ACTH (before: 11·2 ± 1·6 pmol/l; 6th month: 19·4 ± 2·7) and in ghrelin‐stimulated peak ACTH values occurred after 6 months (before: 59·8 ± 15·4; 6th month: 112·0 ± 11·2). GHRP‐6‐induced ACTH release also increased (before: 60·7 ± 17·2; 6th month: 78·5 ± 12·1), although not significantly. Conclusions The rise in basal ACTH levels during ketoconazole treatment in CD could be because of the activation of normal corticotrophs, which were earlier suppressed by hypercortisolism. The enhanced ACTH responses to ghrelin after ketoconazole in CD could also be due to activation of the hypothalamic–pituitary–adrenal axis and/or to an increase in GHS‐receptors expression in the corticotroph adenoma, consequent to reductions in circulating glucocorticoids.     

GHRP-6 is able to stimulate cortisol and ACTH release in patients with Cushing's disease: comparison with DDAVP

It has been shown that hexarelin stimulates ACTH and cortisol secretion in patients with Cushing's disease. The ACTH release induced by this peptide is 7-fold greater than that obtained by hCRH. The mechanism of action of hexarelin on the hypothalamic-pituitary-adrenal axis has not been fully elucidated. Although controversial, there is evidence that it might be mediated by arginine vasopressin (AVP). The aim of this study was to evaluate the ACTH and cortisol releasing effects of GHRP-6 in patients with Cushing's disease and to compare them with those obtained with DDAVP administration. We studied 10 patients with Cushing's disease (8 female, 2 male; age: 36.7 +/- 4.2 yr), 9 with microadenomas, who were submitted to both GHRP-6 (2 microg/kg iv) and DDAVP (10 micro g i.v.) in bolus administration on 2 separate occasions. ACTH was measured by immunochemiluminometric assay and cortisol by radioimmunoassay. The sensitivities of the assays are 0.2 pmol/l for ACTH, and 11 nmol/l for cortisol. GHRP-6 was able to increase significantly both ACTH (pmol/l, mean +/- SE; basal: 15.5 +/- 1.7 vs peak: 45.1 +/- 9.3) and cortisol values (nmol/l, basal: 583.0 +/- 90.8 vs peak: 1013.4 +/- 194.6). ACTH AUC (pmol/l min(-1)) and cortisol AUC (nmol/l min(-1)) values were 1235.4 and 20577.2, respectively. After DDAVP administration there was a significant increase in ACTH (basal: 13.0 +/- 1.4 vs peak: 50.5 +/- 16.2) and cortisol levels (basal: 572.5 +/- 112.7 vs peak: 860.5 +/- 102.8. AUC values for ACTH and cortisol were 1627.6 +/- 639.8 and 18364.7 +/- 5661.4, respectively. ACTH and cortisol responses to GHRP-6 and DDAVP did not differ significantly (peak: 45.1 +/- 9.3 vs 50.5 +/- 16.2; AUC: 1235.4 +/- 424.8 vs 1627.6 +/- 639.8). There was a significant positive correlation between peak cortisol values after GHRP-6 and DDAVP administration (r = 0.87, p = 0.001). Our results show that GHRP-6 is able to stimulate ACTH and cortisol release in patients with Cushing's disease. These responses are similar to those obtained after DDAVP injection. These findings could suggest the hypothesis that both peptides act by similar mechanisms, either at hypothalamic or pituitary level.     

Effects of ghrelin,GH-releasing peptide-6 (GHRP-6) and GHRH on GH,ACTH and cortisol release in hyperthyroidism before and after treatment

In thyrotoxicosis GH responses to stimuli are diminished and the hypothalamic–pituitary–adrenal axis is hyperactive. There are no data on ghrelin or GHRP-6-induced GH, ACTH and cortisol release in treated hyperthyroidism. We, therefore, evaluated these responses in 10 thyrotoxic patients before treatment and in 7 of them after treatment. GHRH-induced GH release was also studied. Peak GH (μg/L; mean ± SE) values after ghrelin (22.6 ± 3.9), GHRP-6 (13.8 ± 2.3) and GHRH (4.9 ± 0.9) were lower in hyperthyroidism before treatment compared to controls (ghrelin: 67.6 ± 19.3; GHRP-6: 25.4 ± 2.7; GHRH: 12.2 ± 2.8) and did not change after 6 months of euthyroidism (ghrelin: 32.7 ± 4.7; GHRP-6: 15.6 ± 3.6; GHRH: 7.4 ± 2.3), although GH responses to all peptides increased in ~50% of the patients. In thyrotoxicosis before treatment ACTH response to ghrelin was two fold higher (107.4 ± 26.3) than those of controls (54.9 ± 10.3), although not significantly. ACTH response to GHRP-6 was similar in both groups (hyperthyroid: 44.7 ± 9.0; controls: 31.3 ± 7.9). There was a trend to a decreased ACTH response to ghrelin after 3 months of euthyroidism (35.6 ± 5.3; P = 0.052), but after 6 months this decrease was non-significant (50.7 ± 14.0). After 3 months ACTH response to GHRP-6 decreased significantly (20.4 ± 4.2), with no further changes. In hyperthyroidism before treatment, peak cortisol (μg/dL) responses to ghrelin (18.2 ± 1.2) and GHRP-6 (15.9 ± 1.4) were comparable to controls (ghrelin: 16.4 ± 1.6; GHRP-6: 13.5 ± 0.9) and no changes were seen after treatment. Our results suggest that the pathways of GH release after ghrelin/GHRP-6 and GHRH are similarly affected by thyroid hormone excess and hypothalamic mechanisms of ACTH release modulated by ghrelin/GHSs may be activated in this situation.     

Impairment of GH responsiveness to GH-releasing hexapeptide (GHRP-6) in Prader-Willi syndrome.

The aim of this study was to evaluate the GH-releasing activity of a synthetic hexapeptide, GHRP-6, in the Prader-Willi syndrome (PWS). Sixteen PWS patients (7 males and 9 females, aged 12.7-38.3 yr), 15 with essential obesity (OB) (7 males and 8 females, aged 12.9-42.9 yr), and 8 short normal children (SN; 3 males and 5 females, aged 10.2-14.3 yr) underwent 2 tests on separate occasions, being challenged with GHRP-6 (1 microg/kg, iv) or GHRH (1 microg/kg, iv)+PD (60 or 120 mg for children or adults, po). Moreover, in 11 patients with PWS and in the group of SN, the GH response to at least 2 stimulation tests had been previously determined. GH was analyzed either as mean peak values (GHp, mcg/l), or as the area under the curve (AUC, mcg/l/h) and the net incremental area under the curve (nAUC, mcg/l/h). In the group of PWS subjects, GH responses to both GHRP-6 (GHp: 11.4+/-2.0; AUC: 588+/-113; nAUC: 483+/-108) and GHRH+PD (GHp: 7.3+/-1.8; AUC: 486+/-122; nAUC: 371+/-250) were significantly lower than those observed either in OB (GHRP-6: GHp: 25.7+/-3.2, p<0.003; AUC: 1833+/-305, p<0.005; nAUC: 1640+/-263, p<0.0001. GHRH+PD: GHp: 15.1+/-2.4, p<0.009; AUC: 1249+/-248, p<0.003; nAUC: 918+/-230, p<0.006) or in SN patients (GHRP-6: GHp: 39.1+/-3.1, p<0.0001; AUC: 2792+/-158, p<0.0001; nAUC: 2705+/-165, p<0.00005. GHRH+PD: GHp: 27.5+/-3.7, p<0.0001; AUC: 1873+/-251, p<0.0001; nAUC: 1692+/-219, p<0.0005). Unlike control groups, in PWS patients GH levels after GHRP-6 did not differ from those obtained after GHRH+PD. Interestingly, low IGF-I values were present in all PWS subjects. Furthermore, no patient with PWS showed normal GH response to the previously performed GH stimulation tests. As already reported, GH release after GHRP-6 or GHRH+PD was significantly lower in OB than in SN subjects. In conclusion, our data indicate that: 1) GH response to GHRP-6 is clearly impaired in PWS; 2) the blunted GH responses to the provocative stimuli in PWS are not an artifact of obesity; 3) short stature in PWS is caused by a complex dysfunction of the hypothalamo-pituitary structures.     

Effect of one month ketoconazole treatment on GH, cortisol and ACTH release after ghrelin, GHRP-6 and GHRH administration in patients with Cushing's disease

GH responses to ghrelin, GHRP-6, and GHRH in Cushing's disease (CD) are markedly blunted. There is no data about the effect of reduction of cortisol levels with steroidogenesis inhibitors, like ketoconazole, on GH secretion in CD. ACTH levels during ketoconazole treatment are controversial. The aims of this study were to compare the GH response to ghrelin, GHRP-6, and GHRH, and the ACTH and cortisol responses to ghrelin and GHRP-6 before and after one month of ketoconazole treatment in 6 untreated patients with CD. Before treatment peak GH (microg/L; mean +/- SEM) after ghrelin, GHRP-6, and GHRH administration was 10.0 +/- 4.5; 3.8 +/- 1.6, and 0.6 +/- 0.2, respectively. After one month of ketoconazole there was a significant decrease in urinary cortisol values (mean reduction: 75%), but GH responses did not change (7.0 +/- 2.0; 3.1 +/- 0.8; 0.9 +/- 0.2, respectively). After treatment, there was a significant reduction in cortisol (microg/dL) responses to ghrelin (before: 30.6 +/- 5.2; after: 24.2 +/- 5.1). No significant changes in ACTH (pg/mL) responses before (ghrelin: 210.9 +/- 69.9; GHRP-6: 199.8 +/- 88.8) and after treatment (ghrelin: 159.7 +/- 40.3; GHRP-6: 227 +/- 127.2) were observed. In conclusion, after short-term ketoconazole treatment there are no changes in GH or ACTH responses, despite a major decrease of cortisol levels. A longer period of treatment might be necessary for the recovery of pituitary function.     

Growth hormone (GH) rebound rise following somatostatin infusion withdrawal: studies in dogs with the use of GH-releasing hormone and a GH-releasing peptide.

OBJECTIVE: Evidence has been presented that in both animals and humans the rebound secretion of growth hormone (GH) following withdrawal of an infusion of somatostatin (SS) is due to the functional activation of the hypothalamic GH-releasing hormone (GHRH) neurons of the recipient organism. Based on this premise, this study has sought to assess the existence of functional interactions between endogenous GHRH released by a SS infusion withdrawal (SSIW) and growth hormone-releasing peptides (GHRPs), a class of compounds allegedly acting via GHRH. METHODS: Five young dogs (3 to 4 years old, 2 male and 3 female) were administered, on different occasions, three consecutive intravenous boli of physiological saline (0.1 ml/kg), or GHRH (2 microg/kg), or EP92632 (125 microg/kg), a GHRP compound, or GHRH plus EP92632 at the end of three cycles of 1-h SS infusions (8 microg/(kg x h)) or during a 6-h infusion of saline. RESULTS: Under saline infusion (SALI), plasma GH levels were unaltered, whereas each SSIW cycle was followed by similar GH secretory episodes. Administration of the first GHRH bolus under SALI induced a rise in plasma GH concentrations slightly higher than that induced by the first cycle of SSIW, but the GH response to the second and third GHRH boli was similar to that after SSIW. Following SSIW, the response to the first bolus of GHRH was higher than that during SALI, but the second and third cycles of SSIW induced GH responses similar to those evoked by the GHRH bolus. During SALI, administration of the first bolus of EP92632 induced a rise in plasma GH which was higher than that induced by the first GHRH bolus, the second bolus elicited a GH peak of lesser amplitude and there was a partial restoration of the GH response to the third peptide bolus. SSIW strikingly enhanced the GH release to the first EP92632 bolus, a pattern also present, although to a lesser extent, with the second and third cycles of SSIW. Under SALI, combined administration of GHRH and EP92632 had a synergistic effect on GH release, but a progressive reduction was present in the GH response to the second and third GHRH plus EP92632 boli. SSIW increased only weakly the GH response to the first co-administration of the peptides over that present after administration of EP92632 alone, and did not induce a GH response higher than that present during SALI when the second bolus of the peptides was administered; after the third SSIW a GH rise higher than that present during SALI was elicited by the combined administration of the peptides. CONCLUSIONS: (i) the uniformity of the GH rebound responses to multiple cycles of SSIW may indicate that the latter activate a physiological mechanism which mimics that normally controlling GH pulse generation; (ii) EP92632 elicits, under our experimental conditions, a plasma GH rise higher than that induced by GHRH; (iii) SSIW enhances the GH response to EP92639 alone, to an extent reminiscent of that following combined administration of GHRH and EP92632. This pattern reinforces the view that SSIW elicits release of endogenous GHRH, and infers that the GHRP challenge after SSIW may be exploited in humans to distinguish between healthy and GH-deficient adults.     

Selective lack of growth hormone (GH) response to the GH-releasing peptide hexarelin in patients with GH-releasing hormone receptor deficiency

The mechanism of the synergistic relationship between GH-releasing peptide (GHRP) and GHRH with respect to GH secretion is poorly understood. We report the response to hexarelin, a potent GHRP, in patients affected with a homozygous mutation in the GHRH receptor gene, with consequent GHRH resistance and GH-deficient dwarfism. This newly described syndrome is the human homolog of the little (lit/lit) mouse. Intravenous administration of hexarelin (2 microg/kg) to four male adult patients (dwarfs of Sindh) resulted in a complete lack of elevation in plasma GH levels (< 1 ng/mL), an at least 50- to 100-fold deviation from the normal response. In contrast, plasma PRL, ACTH, and cortisol levels rose in a normal manner in response to hexarelin. We conclude that an intact GHRH signaling system is critical for GHRPs to exert their effect on GH release, but that the GHRH system is not necessary for the effect of GHRP on PRL and ACTH secretion. Hexarelin (and probably other GHRPs) are not effective agents for the treatment of patients with GHRH resistance due to GHRH receptor deficiency.     

Growth hormone (GH)-releasing peptide stimulates GH release in normal men and acts synergistically with GH-releasing hormone

The acute GH release stimulated by the synthetic hexapeptide, His-DTrp-Ala-Trp-DPhe-Lys-NH2 [GH releasing peptide (GHRP)], was determined in 18 normal men and compared with the effects of GH-releasing hormone, GHRH-(1-44)-NH2. Specificity of effect was assessed by measurement of serum PRL, LH, TSH, and cortisol. GHRP was administered at doses of 0.1, 0.3, and 1.0 microgram/kg by iv bolus. GHRH at a dose of 1.0 microgram/kg was administered alone and together with various does of GHRP. No adverse clinical effects of laboratory abnormalities were observed in response to GHRP. A side-effect of mild facial flushing of 1- to 3-min duration occurred in 16 of the 18 subjects who received GHRH-(1-44)-NH2. Mean (+/- SEM) peak serum GH levels after injection of placebo and 0.1, 0.3, and 1.0 microgram/kg GHRP were 1.2 +/- 0.3, 7.6 +/- 2.5, 16.5 +/- 4.1, and 68.7 +/- 15.5 micrograms/L, respectively. The submaximal dosages of 0.1 and 0.3 microgram/kg GHRP plus 1 microgram/kg GHRH stimulated GH release synergistically. Serum PRL and cortisol levels rose about 2-fold above basal levels only at the 1 microgram/kg dose of GHRP, and there were no changes in serum LH and TSH over the first hour after administration of the peptide(s). GHRP is a potent secretagogue of GH in normal men. Since GHRP and GHRH together stimulate GH release synergistically, these results suggest that GHRP and GHRH act independently. This supports our hypothesis that the GH-releasing activity of GHRP reflects a new physiological system in need of further characterization in animals and man.     

Effects of short-term glucocorticoid deprivation on growth hormone (GH) response to GH-releasing peptide-6: studies in normal men and in patients with adrenal insufficiency

There are no data in the literature about the effects of glucocorticoid deprivation on GH-releasing peptide-6 (GHRP-6)-induced GH release. The aims of this study were to evaluate GH responsiveness to GHRP-6 1) after metyrapone administration in normal men, and 2) in patients with chronic hypocortisolism after glucocorticoid withdrawal for 72 h. In normal subjects, metyrapone ingestion did not alter significantly GH responsiveness to GHRP-6 [n = 8; peak, 39.3 +/-7.1 microg/L; area under the curve (AUC), 1958.8 +/- 445.7 microg/min x L; mean +/- SE] compared to placebo (n = 8; peak, 21.9 +/- 4.5; AUC, 1131.0 +/- 229.6). In patients with chronic hypocortisolism (n = 8), GH responses to GHRP-6 were similar both during replacement therapy (peak, 11.8 +/- 3.9; AUC, 563.2 +/- 208.7) and after withdrawal of prednisone (peak, 14.4 +/- 4.5; AUC, 695.6 +/- 272.9) and did not differ from those in controls. Interestingly, after glucocorticoid withdrawal, GH responsiveness to GHRP-6 in patients with chronic hypocortisolism was significantly lower than that in normal subjects pretreated with metyrapone. Our data suggest that short term glucocorticoid deprivation does not have a major impact on GHRP-6-dependent GH-releasing mechanisms. However, in long standing hypocortisolism, subtle changes in GHRP-6 secretory pathways may be present.     

Growth hormone response to GHRH, GHRP-6 and GHRH+GHRP-6 in patients with polycystic ovary syndrome

OBJECTIVE A number of long-term research studies are in progress to evaluate the effects of treatment with GH on growth and final height in children with short stature but no demonstrable abnormality of GH secretion. Such treatment is invasive, expensive and carries some risk to the child. An early indication of growth response would allow restriction of treatment to those children most likely to benefit, but anthropometric measurements are relatively subjective, insensitive and imprecise. The aim of this study was to evaluate bone alkaline phosphatase, procollagen Type I C-terminal propeptide, procollagen Type III N-terminal propeptide and the cross-linked carboxyterminal telopeptide of Type I collagen as early biochemical predictors of height velocity response to growth-promoting treatments in short normal children. DESIGN A prospective intervention study, partially placebo controlled on a double blind basis. PATIENTS Fifty healthy children with familial short stature or constitutional delay in growth and puberty (8 girls, 42 boys, ages 5.5–16.5 years and all either prepubertal (45) or in very early puberty (5 boys) at the start of treatment) were treated with placebo (6), GH alone (32), GH plus oxandrolone (8) or GH plus testosterone (4). MEASUREMENTS Bone alkaline phosphatase and the collagen markers were measured at the start of treatment and 3 months later. Height velocity was calculated at the start of treatment and again after one year. RESULTS Pre-treatment biochemical marker concentrations did not predict height velocity response after one year. Increments in all markers after 3 months were significantly correlated with height velocity increments after one year of treatment, the highest correlations being observed for bone alkaline phosphatase (r = 0.67, P < 0.0001) and procollagen Type III N-terminal propeptide (r = 0.57, P < 0.0001). Highly significant correlations (P < 0.0001) were also observed between bone alkaline phosphatase and procollagen Type I C-terminal propeptide (r = 0.55) and between procollagen Type III N-terminal propeptide and the cross-linked carboxyterminal telopeptide of Type I collagen (r = 0.62). Multiple linear regression with stepwise selection of variables identified bone alkaline phosphatase and procollagen Type III N-terminal propeptide as the only two independent variables that contributed significantly to the prediction of height velocity response after one year (analysis of variance, P < 0.0001). Together they predicted 59% of the variability in height velocity response after a year. CONCLUSIONS The best early predic tors of height velocity response were bone alkaline phosphatase (a protein found in hypertrophic chondrocytes in the epiphyseal growth plate, in calcifying matrix vesicles and in mature osteoblasts) and procollagen Type III N-terminal propeptide, a marker of interstitial fibril biosynthesis in soft tissues. Using these markers, GH treatment could be targeted to those children most likely to benefit in the medium term.     

Postprandial changes in plasma GH and insulin concentrations, and responses to stimulation with GH-releasing hormone (GHRH) and GHRP-6 in calves around weaning

Changes in plasma concentrations of GH and insulin in response to feeding and stimulation with GH-releasing hormone (GHRH) or GH-releasing peptide (GHRP-6, a ligand for endogenous GH secretagogue receptors) were compared between 3-week-old (milk-fed) and 12-week-old (concentrate and hay-fed) calves. Feeding of a milk-replacer diet in 3-week-old animals significantly increased the basal (prefeeding) concentrations of GH, insulin and glucose in plasma, whereas feeding of concentrate and hay in 12-week-old animals did not cause a significant change in these traits. However, in the animals maintained on a milk-replacer diet until 12 weeks of age, postprandial plasma GH concentrations and AUC (area under the curve) were not different from those in the age-matched weaned group. The venous injection of either GHRH (0.25 microg/kg) or GHRP-6 (2.5 microg/kg) significantly increased plasma GH concentrations in both 3- and 12-week-old animals, but GH AUC was significantly greater in 3-week-old than in 12-week-old animals. Insulin concentration was transiently but significantly increased by the injection of GHRP-6 only in 12-week-old animals, the AUC being greater in 12-week-old than 3-week-old animals. From these results, we conclude that postprandial levels of plasma GH and insulin concentrations are altered after weaning and by aging, and that the quality of diets or development of the neuroendocrine functions in the digestive-pituitary system may be involved in this alteration.     

Growth hormone (GH) response to GH-releasing peptide-6 and GH-releasing hormone in normal-weight and overweight patients with non-insulin-dependent diabetes mellitus

The growth hormone (GH) response to GH-releasing hormone (GHRH) in patients with non-insulin-dependent diabetes mellitus (NIDDM) was found to be either decreased or normal. The recent introduction of a new and potent GH stimulus, GH-releasing peptide-6 (GHRP-6), allowed further investigation of the functional properties of somatotropes in a variety of metabolic diseases. The aim of the present study was to investigate the response of GH to GHRP-6, GHRH, and GHRP-6 + GHRH in NIDDM patients. Twenty-one patients with NIDDM were divided into two groups: group A, normal weight (body mass index [BMI], 23.31+/-0.62 kg/m2); and group B, overweight (BMI, 27.62+/-0.72 kg/m2). Eight normal-weight control subjects (group C) were studied. Each subject received GHRP-6 (90 microg intravenously [i.v.]), GHRH (100 microg i.v.), and GHRP-6 + GHRH on three separate occasions. There was no difference between the GH response after GHRP-6 in groups A, B, and C in terms of the GH peak (50.95+/-11.55, 51.96+/-7.71, and 70.07+/-15.59 mU/L, P>.05) and the area under the curve (AUC) for GH (2,340.06+/-617.36, 2,684.54+/-560.57, 3,462.78+/-1,223.53 mU/L/120 min, P>.05). A decreased GH response to GHRH was found in group B in comparison to group A (B v A: peak GH response, 8.25+/-1.90 v 22.19+/-8.81, P<.05; AUC GH, 479.62+/-84.0 v 1,443.21+/-743.76, P<.05). There was no difference in the GH response between group A and group C (peak GH response, 22.19+/-8.81 v 26.42+/-6.71, P>.05; AUC, 1,443.21+/-743.76 v 1,476.51+/-386.56, P>.05). There was a significant difference between the same parameters in group B versus group C (8.25+/-1.90 v 26.42+/-6.71, P<.05; AUC, 479.62+/-84.0 v 1,476.51+/-386.56, P<.05). The combined administration of GHRP-6 + GHRH elicited a synergistic GH response in NIDDM patients and controls. There was a significant difference between groups A and B for the GH peak (96.49+/-9.80 v 68.38+/-8.25, P<.05), whereas there was no difference for the AUC (5,111.13+/-703.77 v 3,425.95+/-459.67, P>.05). There was no difference in the peak GH after the combined test between group A and group C (96.49+/-9.80 v 139.82+/-24.16, P>.05), whereas the peak GH in the same test was significantly decreased in group B in comparison to group C (68.38+/-8.25 v 139.82+/-24.16, P<.05). The AUC for GH after combined GHRP-6 + GHRH in group A versus group C was not significantly different (5,111.13+/-703.77 v 9,274.71+/-1,541.46, P>.05), whereas there was a significant difference for the same test between group B and group C (3,425.95+/-459.67 v 9,274.71+/-1,541.46, P<.05). Our results demonstrate that normal-weight NIDDM patients have a preserved GH response to GHRP-6, GHRH, and GHRP-6 + GHRH, and overweight NIDDM patients have a blunted response to GHRH and GHRP-6 + GHRH. The preserved GH response to GHRP-6 in both diabetic groups suggests that the secretory potential of somatotropes is preserved in NIDDM patients. The impairment of the GH response to GHRH in overweight NIDDM patients could be a functional defect due to the obesity, since it could be overridden by administration of GHRP-6.     

Inhibition of growth hormone release after the combined administration of CHRH and GHRP-6 in patients with Cushing's syndrome

OBJECTIVE In patients with Cushing's syndrome there is a blunted OH response to all types of stimuli. Although Inferential data point towards a direct perturbation in the pituitary exerted by glucocorticoids, the bask mechanism is unknown. His-d -TRP-ALA-TRP-d -Phe-Lys-NH₂ (GHRP-6) is a synthetic hexapeptlde which releases GH by a direct pituitary effect through receptors other than GHRH receptors. Furthermore, the combined administration of GHRH and GHRP-6 is able to induce a large OH discharge even in some pathological states such as obesity, associated with GH blockade. To gain further insight into the disrupted mechanisms of GH secretion, Cushing's syndrome patients were challenged with either GHRH, GHRP-6 or GHRH together with GHRP-6. A group of normal subjects was included for control purposes. DESIGN Three different tests were undertaken: (a) GHRH 100 μg I.v.; (b) GHRP-6 100 μg I.v. and (c) GHRH plus GHRP-6 100 μg I.v. of each; administered to each subject on different days, at least 4 days apart. PATIENTS Ten patients (8 women, 2 men) with untreated Cushing's syndrome, 9 Cushing's disease and 1 adrenal adenoma. Five healthy volunteers (3 women, 2 men) of similar ages served as a control group. MEASUREMENTS Plasma OH levels were measured by immunoradiometric assay. RESULTS The areas under the curve (AUC) of OH secretion (mean ± SEM In μ/1/120 mi) in the control subjects after each test were: GHRH, 1420 ± 330; GHRP-6, 2278 ± 290 and GHRH plus GHRP-6,7332 ± 592 (P < 0·05 vs each compound alone). The AUCs for Cushing's syndrome patients were: GHRH, 248 ± 165; GHRP-6 530 ±170 and for GHRH plus GHRP-6, 870 ± 258 (P < 0·05 vs GHRH alone). After the combined stimulus only one out of the ten patients with hypercortisolism showed a GH peak over 20 μ/l, while ail the controls had a peak over 04mU/l. CONCLUSIONS GHRP-6 induced OH secretion as well as the OH discharge elicited by GHRH and GHRP-6 are considerably reduced in Cushing's syndrome patients. This suggests that the main impairment of GH secretion in that pathological state resides at pituitary level.     

An assessment of bone mineral density in patients with Addison's disease and isolated ACTH deficiency treated with glucocorticoid

Glucocorticoid replacement therapy needs to be tailored to individual patient's requirements in order to avoid risk of over or under medication. We measured bone mineral density (BMD) of lumbar spine using dual X-ray absorptiometory in 10 patients with Addison's disease and 5 patients with isolated ACTH deficiency receiving glucocorticoid replacement therapy. We also examined the effect of glucocorticoid replacement on BMD. Decreased %BMD (less than 80% of age-matched controls) was found in 2 female patients who had received hydrocortisone at a dose of 14.8 and 15.4 mg/m(2)/day. In contrast, no patient receiving a hydrocortisone dose of less than 12.4 mg/m (2)/day had decreased %BMD. There was no correlation between %BMD and hydrocortisone dose (mg/m(2)), duration of therapy, or cumulative hydrocortisone dose when treated with appropriate dose of hydrocortisone (<13.6 mg/m(2)). There was also no statistically significant difference in %BMD with age. We concluded that long-term glucocorticoid replacement therapy does not induce bone loss in patients with glucocorticoid deficiency unless an excessive dose of hydrocortisone is given.     

Growth hormone (GH) responses to the hexapeptide GH-releasing peptide and GH-releasing hormone (GHRH) in the cynomolgus macaque: evidence for non-GHRH-mediated responses.

GH-releasing peptide (GHRP; His-D-Trp-Ala-Trp-D-Phe-Lys-NH2), a hexapeptide derived from enkephalin, has been shown to have GH-releasing activity in man and several animal species. To characterize the GHRP dose-response curve and compare it with that of GH-releasing hormone [GHRH-(1-44)NH2], six unanesthetized young adult cynomolgus macaques were tested with a range of iv doses of GHRP or GHRH in random order. Animals were fitted with vests and tethers. Blood samples were obtained before and at 15-min intervals after the administration of drugs. Doses ranged from 0.03-3 mg/kg for GHRP and from 1-30 micrograms/kg for GHRH. The dose-response curves for the two peptides were not parallel. GHRP had lower potency, but evoked a much higher peak GH response than GHRH (greater than 55 vs. 12 micrograms/L). Because one of the proposed mechanisms of action of GHRP is the inhibition of somatostatin (SS), we tested the effects of propranolol, which inhibits SS, on the GH responses to GHRH and GHRP. Propranolol was given at a dose of 14 micrograms/kg, iv, 10 min before the injection of saline, GHRH (10 micrograms/kg), or GHRP (1 mg/kg). GH responses to propranolol alone did not differ from those to placebo (peak, 6 +/- 2 vs. 8 +/- 2 micrograms/L). However, propranolol pretreatment doubled the GH responses to both GHRH and GHRP compared with those to GHRH or GHRP alone 28 +/- 5 micrograms/L vs. 14 +/- 5 (P less than 0.05) and 54 +/- 2 vs. 25 +/- 6 micrograms/L (P less than 0.001), respectively]. These results show that GHRP causes a potent dose-dependent release of GH in this primate species. Since GHRP can produce a greater maximal GH response than GHRH, mechanisms other than release of endogenous GHRH must be involved.