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An endogenous ligand for the GH secretagogue-receptor (GHS-receptor) has recently been isolated, from both the rat and the human stomach, and named ghrelin. It is a 28-amino-acid peptide showing a unique structure with an n-octanoyl ester at its third serine residue, which is essential for its potent stimulatory activity on somatotroph secretion. In fact, it has been demonstrated that ghrelin specifically stimulates GH secretion from both rat pituitary cells in culture and rats in vivo. The aim of the present study was to test the GH-releasing activity of ghrelin in humans and to compare it with that of GHRH and hexarelin (HEX), a nonnatural peptidyl GHS, which possesses strong GH-releasing activity but also significantly stimulates PRL, ACTH, and cortisol secretion. To clarify the mechanisms of action underlying the GH-releasing activity of ghrelin in humans, its interaction with GHRH and HEX was also studied. Seven normal young volunteers (7 men; 24-32 yr old; body mass index, 20-24 kg/m(2)) were studied. All subjects underwent the administration of ghrelin, HEX, and GHRH-29 (1.0 microg/kg i.v. at 0 min) as well as placebo (2 mL isotonic saline i.v. at 0 min). Six subjects also underwent the combined administration of ghrelin and GHRH or HEX. Blood samples were taken every 15 min from -15 up to +180 min. GH levels were assayed at each time point in all sessions; PRL, ACTH, cortisol, and aldosterone levels were also assayed after administration of ghrelin and/or HEX. Ghrelin administration induced a prompt and marked increase in circulating GH levels (Cmax, mean +/- SEM, 92.1 +/- 16.7 microg/L; area under the curve, 1894.9 +/- 347.8 microg/L.h). The GH response to ghrelin was clearly higher (P < 0.01) than the one recorded after GHRH (26.7 +/- 8.7 microg/L; 619.6 +/- 174.4 microg/L.h) and even significantly higher (P < 0.05) than after HEX (68.4 +/- 14.7 microg/L; 1546.9 +/- 380.0 microg/L x h). Ghrelin administration also induced an increase in PRL, ACTH, and cortisol levels; these responses were higher (P < 0.05) than those elicited by HEX. A significant increase in aldosterone levels was recorded after ghrelin but not after HEX. The endocrine responses to ghrelin were not modified by the coadministration of HEX. On the other hand, the coadministration of ghrelin and GHRH had a real synergistical effect (P < 0.05) on GH secretion (133.6 +/- 22.5 microg/L; 3374.3 +/- 617.3 microg/L x h). In conclusion, ghrelin, a natural ligand of GHS-receptor, exerts a strong stimulatory effect on GH secretion in humans, releasing more GH than GHRH and even more than a nonnatural GHS such as HEX. Ghrelin, as well as HEX, also stimulates lactotroph and corticotroph secretion. Ghrelin shows no interaction with HEX, whereas it has a synergistical effect with GHRH on GH secretion. Thus, ghrelin is a new hormone playing a major role in the control of somatotroph secretion in humans, and its effects are imitated by nonnatural GHS.

GH-releasing peptides (GHRPs) are synthetic, nonnatural molecules that strongly stimulate GH secretion, but also slightly increase PRL, ACTH, and cortisol levels in man. To investigate the mechanism underlying the ACTH- and cortisol-releasing activity of GHRPs in man, we compared the ACTH- and cortisol-releasing activity of Hexarelin (HEX; 2.0 μg/kg, iv), a hexapeptide belonging to the GHRP family, with that of human CRH (hCRH; 2.0 μg/kg, iv) in normal subjects (6 men and 6 women, 24–68 yr old) and patients with Cushing’s syndrome (2 men and 15 women, 16–68 yr old). The GH response to HEX administration was also studied. In normal subjects, HEX administration significantly increased ACTH (peak vs. baseline, mean ± sd, 32.4± 17.7 vs. 16.3 ± 7.2 pg/mL; P < 0.005) and cortisol levels (135.9 ± 51.0 vs. 110.0 ± 31.6 μg/L; P < 0.01). The ACTH and cortisol responses to hCRH [35.7 ± 13.2 vs. 17.1± 7.7 pg/mL (P < 0.01) and 162.8 ± 50.1 vs. 102.8 ± 28.1 μg/L (P < 0.01), respectively] were similar to the responses t...

Hexarelin (HEX) is a synthetic growth-hormone-releasing peptide (GHRP) which acts via specific receptors at both the pituitary and the hypothalamic level to stimulate GH release both in animals and in man. Like other GHRPs, HEX possesses also significant prolactin- and adrenocorticotropin (ACTH) cortisol-releasing activity, but the mechanisms underlying these effects are even less clear. To clarify the mechanisms by which HEX stimulates the pituitary-adrenal axis in man, in 7 healthy young volunteers we studied the effects of HEX (2.0 microg/kg i.v.) and/or human corticotropin-releasing hormone (hCRH; 2.0 microg/kg i.v.) and/or arginine vasopressin (AVP; 0.17 U/kg i.m.) on ACTH and cortisol secretion. The GH responses to HEX alone and combined with hCRH and/or AVP were also studied. HEX increased ACTH and cortisol secretion (peak, mean +/- SEM: 26.3 +/- 5.1 vs. 15.8 +/- 3.1 pg/ml and 145.0 +/- 11.4 vs. 131.7 +/- 11.7 microg/l, p < 0.01, respectively) to levels overlapping with those induced by AVP (27.9 +/- 6.1 vs. 13.1 +/- 3.5 pg/ml and 167.6 +/- 16.2 vs. 113.3 +/- 9.4 microg/l, p < 0.01, respectively) and similar to those elicited by hCRH (28.1 +/- 4.6 vs. 17.4 +/- 3.1 pg/ml and 182.7 +/- 22.8 vs. 114.8 +/- 12.3 microg/l, p < 0.02, respectively). The ACTH but not the cortisol response to hCRH was higher (p < 0.02) than those to HEX when evaluated as area under the curve. The co-administration of HEX and AVP had no significant interaction on ACTH and cortisol peak levels (40.7 micro 5.3 pg/ml and 168.8 +/- 13.5 microg/l, respectively). On the other hand, the co-administration of HEX and hCRH had a less than additive effect on ACTH and cortisol secretion (53.3 +/- 11.2 pg/ml and 204.0 +/- 13.7 microg/l, respectively). CRH and AVP had a true synergistic effect on ACTH (104.9 +/- 14.2 pg/ml, p < 0.01) and an additive effect on cortisol secretion (281.3 +/- 10.8 microg/l, p < 0.02). HEX did not modify the effect of CRH + AVP on both ACTH (135.5 +/- 22.0 pg/ml) and cortisol secretion (261.1 +/- 13.2 microg/l). The GH response to HEX (55.7 +/- 19.8 vs. 2.7 +/- 1.9 microg/l, p < 0.005) was unaffected by the administration of CRH alone (53.5 +/- 21.0 microg/l) and/or AVP co-administration (60.2 +/- 21.2 and 45.9 +/- 10.6 microg/l, respectively). In conclusion, the results of this study demonstrate that GHRPs, beside their well-known GH-releasing activity, possess a remarkable ACTH-releasing activity, overlapping with that of AVP and similar to that of hCRH, two neurohormones which are known to play the major role in the control of the pituitary-adrenal axis. It is noteworthy that HEX shows no synergistic effect with either AVP or hCRH which, on the other hand, truly synergize. This evidence suggests the hypothesis that the ACTH-releasing activity of GHRPs could be, at least partially, independent of both CRH- and AVP-mediated actions in humans.

Ghigo E, Ceda GP, Valcavi R, Goffi S, Zini M, Mucci M, Valenti G, Muller EE, Camanni F. Effect of 15-day treatment with growth hormone-releasing hormone alone or combined with different doses of arginine on the reduced somatotrope responsiveness to the neurohormone in normal aging. Eur J Endocrinol 1995;132:32–6. ISSN 0804–4643 It is well known that both spontaneous and growth hormone-releasing hormone (GHRH)-stimulated GH secretion undergo an age-related decrease; in addition, there is supportive evidence that the GH hyposecretory state of aging is of hypothalamic origin. The aims of the study in 35 normal elderly subjects (20 males and 15 females aged 65–89 years) were to verify whether the low somatotrope responsiveness to GHRH (1 μg/kg) can be primed by a daily GHRH treatment and whether the potentiating effect of both high intravenous (0.5 g/kg) and low oral (8 g) doses of arginine (ARG) on GH response to GHRH is maintained with time. In group A (N = 14) the GH response to GHRH on day 1 (AUC: 373.5 ± 78.5 μg·1−1·h−1) was unchanged after 7 (3720 ± 38 μg·1−1·h−1) and 15 days (377.9 ± 63.8 μg·1−1·h−1) of daily GHRH administration. In group B (N = 6) the GH response to GHRH co-administered with iv ARG on day 1 (1614.2 ± 146.2 μg · 1−1 · h−1) was higher (p < 0.05) than that of GHRH alone (group A) and persisted unchanged after 7 (1514.7±366.5 μg·1−1·h−1) and 15 days (1631.7 ± 379.1 μg · 1−1 · h−1) of treatment. In group C (N = 15) the GH response to GHRH co-administered with oral ARG on day 1 (950.6 ± 219.4 μg·1−1 · h−1) was higher (p < 0.03) than that of GHRH alone (group A) but lower (p < 0.05) than that to GHRH plus iv ARG (group B). It was unchanged after 7 (816.2 ± 208.5 μg·1−1 · h−1) and 15 days (760.4 ± 165.0 μg · 1−1· h−1) of treatment; these responses were still higher (p < 0.05) than that to GHRH alone. Insulin-like growth factor I levels were not modified by any of the treatments. In conclusion, our results demonstrate that in normal aging the low somatotrope responsiveness to GHRH is not improved by prolonged treatment with the neurohormone but it is enhanced by the combined treatment with ARG and this effect does not vanish after a 15-day treatment period. The effect of ARG is present even after a low oral dose, although less markedly than after a high intravenous dose. F Camanni, Divisione di Endocrinologia, Ospedale Molinette, C. so Dogliotti 14, 10126 Torino, Italy

At present, the most appropriate method for diagnosing GH deficiency (GHD) in adults remains unclear. Recently, it has been demonstrated that GHD in adults can be identified by insulin tolerance test (ITT). Moreover, it has been described that the GHRH plus pyridostigmine (GHRH+PD) test is more accurate than an arginine, glucagon, levodopa, or GHRH test to diagnose GHD in adults. In the current study, firstly we reevaluated GH secretion by the GHRH+PD test in adults previously diagnosed as GH deficient in childhood. The study included 69 patients and 38 healthy subjects. After the GHRH+PD test, the patients and the healthy subjects had peak GH levels of 10.6 +/- 11.2 and 56.7 +/- 28.1 micrograms/L, respectively (P < 0.001). The patients were divided into two groups, responder patients and nonresponder patients, considering an arbitrary cut-off of 10 micrograms/L as the GH peak after the GHRH+PD test. Thirty-nine patients had GH peak below 10 micrograms/L (1.9 +/- 1.7 micrograms/L), whereas the remaining 30 patients above 10 micrograms/L (21.6 +/- 8.] micrograms/L; P < 0.001). Secondly, we compared the GHRH+PD test and the ITT in diagnosing GHD. Twenty-one of the 39 patients with a GH peak below 10 micrograms/L and 29 of the 30 patients with a GH peak above 10 micrograms/L after the GHRH+PD test underwent an ITT. The GH peak after insulin administration was 2.1 +/- 1.7 micrograms/L in nonresponder patients and 21.1 +/- 9.3 micrograms/L in responder patients after the GHRH+PD test (P < 0.001). Three of the responder patients to the GHRH+PD test were identified as GH deficient by the ITT. The relative diagnostic accuracies of the two tests to discriminate GH-deficient patients from healthy subjects were similar (ITT vs. GHRH test: sensitivity, 100%, specificity, 90%; GHRH+PD vs. ITT; sensitivity, 88%; specificity, 100%). In conclusion, in adults previously diagnosed as GH deficient, it is mandatory to reevaluate GH secretion. GHRH+PD and/or ITT are able to diagnose GHD in adults with similar accuracies. Taking into account the potential side-effects of the ITT, however, the GHRH+PD test is the most reliable and safe test to accurately diagnose GHD status in adults.

Animal studies indicate that mineralocorticoid receptors (MR) in the hippocampus play a major role in the glucocorticoid feedback control of the hypothalamo-pituitary-adrenal (HPA) axis. Specifically, MR mediate the proactive feedback of glucocorticoids in the maintenance of basal HPA activity. The stimulatory effect of intracerebroventricular and intrahippocampal MR blockade on the HPA axis in animals has been clearly shown, whereas the effect of systemic administration of mineralocorticoid antagonists in humans is still contradictory. To clarify this point, in seven normal young women (aged 25-32 yr; body mass index, 19.0-23.0 kg/m(2)) we studied the effects of canrenoate (CAN; 200 mg as iv bolus at 2000 h, followed by 200 mg infused in 500 mL saline over 4 h up to 2400 h) or placebo (saline, 1.0 mL as iv bolus at 2000 h, followed by 500 mL over 4 h up to 2400 h) on the spontaneous ACTH, cortisol, dehydroepiandrosterone (DHEA) and aldosterone secretion as well as on the ACTH, cortisol, and DHEA responses to human CRH (2.0 microg/kg as iv bolus at 2200 h) or arginine vasopressin (AVP; 0.17 U/kg as im bolus at 2200 h). Blood samples were taken every 15 min from 2000-2400 h. During placebo, spontaneous ACTH and cortisol levels showed progressive decreases (P0.05) from 2000-2400 h (baseline vs. nadir, mean +/- SEM, 2.0 +/- 0.3 vs. 1.4 +/- 0.2 pmol/L and 115.1 +/- 23.7 vs. 63.5 +/- 24.3 nmol/L), whereas DHEA and aldosterone levels did not change. CRH induced clear increases in ACTH, cortisol, and DHEA levels (peaks, mean +/- SEM, 7.1 +/- 1.1 vs. 1.6 +/- 0.2 pmol/L, 322.9 +/- 19.5 vs. 92.8 +/- 24.5 nmol/L, and 44.2 +/- 2.7 vs. 20.0 +/- 3.0 nmol/L; P0.05). Similarly, AVP elicited significant increases in ACTH, cortisol, and DHEA levels (3.8 +/- 0.3 vs. 1.5 +/- 0.1 pmol/L, 211.9 +/- 27.2 vs. 67.7 +/- 9.7 nmol/L, and 51.6 +/- 4.0 vs. 16.3 +/- 2.0 nmol/L; P0.05). During CAN treatment, ACTH, cortisol, and DHEA levels showed progressive rises, which begun at approximately 60 min and peaked between 2300 and 2400 h (ACTH, 3.4 +/- 0.4 vs. 1.1 +/- 0.3 pmol/L; cortisol, 314.5 +/- 49.6 vs. 123.3 +/- 13.2 nmol/L; DHEA, 52.0 +/- 8.8 vs. 21.0 +/- 2.3 nmol/L; P0.05 vs. baseline as well as vs. the same time points during placebo). Aldosterone secretion was not modified by CAN. The ACTH, cortisol, and DHEA responses to human CRH were enhanced by CAN (10.0 +/- 1.7 pmol/L, 462.2 +/- 36.9 nmol/L, and 66.3 +/- 8.8 nmol/L), although statistical significance (P0.05) was obtained for cortisol and DHEA only. Also the ACTH, cortisol and DHEA responses to AVP were amplified by CAN (8.0 +/- 2.6 pmol/L, 324.0 +/- 34.8 nmol/L, and 77.8 +/- 4.0 nmol/L); again, statistical significance (P0.05) was obtained for cortisol and DHEA only. In conclusion, our study shows that the blockade of MR by CAN significantly enhances the activity of the HPA axis in humans, indicating a physiological role for MR in its control. These results also suggest that the stimulatory effect of CAN on HPA axis is mediated by concomitant modulation of CRH and AVP release.

The activity of the growth hormone (GH)-insulin-like growth factor-I (IGF-I) axis undergoes marked variations across the human life span, mainly reflecting age-related changes in the neural control of somatotroph function. IGF-I secretion generally reflects GH status, except in newborns, who secrete high levels of GH but low levels of IGF-I. Changes in the gonadal steroid milieu, particularly estradiol, play a major role in the enhanced activity of the GH-IGF-I axis at puberty and probably reflect further changes in the neuroendocrine control of somatotroph secretion. The change in responsiveness of somatotrophs to various stimuli, including GHRH, is not as marked as the spontaneous secretion of GH at puberty. However, in childhood, somatotrophs are unusually refractory to the somatostatin-mediated negative GH autofeedback mechanism. Normal children show normal responsiveness to the stimulatory influence of alpha-adrenergic and cholinergic agonists, galanin and arginine, but the activating effect of these stimuli on somatotroph secretion is reduced in elderly individuals, with the notable exception of arginine. Arginine potentiates both spontaneous and GHRH-induced GH secretion to the same extent in normally growing children, adults and elderly individuals, indicating that the releasable pool of GH is generally preserved across the human life span. Thus, the reduction in spontaneous and GHRH-induced GH secretion in the elderly probably reflects age-related changes in neurotransmitter control, leading to GHRH hypoactivity and absolute or relative somatostatin hyperactivity in the aged hypothalamus. Cholinergic impairment in the aging brain probably involves hypothalamic pathways and leads to decreased activity of the GH-IGF-I axis in normal and elderly individuals, as well as in individuals with premature brain aging. However, there is evidence indicating that age-related variations in the activity of the natural GH-secretagogue ligand(s) at the hypothalamic level could also play a role in the age-dependent changes in the GH-IGF-I axis.

Either in children or in adults, arginine (ARG) alone and combined with GHRH (GHRH+ARG) are reliable tests for the diagnosis of GH deficiency. The procedures of these tests generally include GH measurement every 15 min from baseline up to 90-120 min. Aim of our study was to verify if the procedure of these tests could be usefully shortened in clinical practice. To this goal we have studied 173 normally growing children and adolescents (C, 117 M and 56 F, age: 11.3 +/- 0.4 yr.) and 125 young and middle aged normal adults (A, 68 M and 57 F, age: 30.0 +/- 0.6 yr.). ARG alone test was performed by 81 C and 33 A (0.5 g/kg arginine, i.v., from 0 to +30 min, up to a maximum of 30 g) while GHRH (1 microg/kg i.v. bolus at 0 min) + ARG test was performed by 92 C and 92 A. After ARG alone, taking into account data from +15 to +105 min, GH values above the 3rd centile limit of arbitrary cut-off (7 or 10 microg/l in C and 5 microg/l in A) occurred in 85% or 64% and 94% subjects, respectively. After GHRH+ARG test, taking into account only data at +30, +45, +60 min GH values above the 3rd centile limit (20 microg/l in C and 16.5 microg/l in A) occurred in 99% of subjects in both groups. Taking into account only these 3 timing points, the percentage of GH peak above the third centile limits after ARG alone was never higher than 60% in C and 85% in A. In conclusion, this study shows that single GHRH+arginine test can be reliably performed in a shortened procedure which makes easier the clinical practice and further reduces costs.

Within an appropriate clinical context, severe GH deficiency (GHD) in adults has to be defined biochemically by provocative testing of GH secretion. Patients with childhood-onset GHD need retesting in late adolescence or young adulthood to verify whether they have to continue recombinant human GH treatment. GHRH + arginine (GHRH+ARG) is the most reliable alternative to the insulin-induced hypoglycemia test (ITT) as a provocative test for the diagnosis of GHD in adulthood, provided that appropriate cut-off limits are assumed (normal limits, 16.5 microg/L as 3rd and 9.0 microg/L as 1st centile). We studied the GH response to a single GHRH (1 microg/kg iv) + ARG (0.5 g/kg iv) test in 62 young patients who had undergone GH replacement in childhood, based on the following diagnosis: 1) organic hypopituitarism with GHD (oGHD) In = 18: 15 male (M), 3 female (F); age, 26.8+/-2.2 yr; GH peak10 microg/L after two classical tests]; 2) idiopathic isolated GHD (iGHD) [n = 23 (15 M, 8 F); age, 23.0+/-1.5 yr; GH peak10 microg/L after two classical tests]; and 3) GH neurosecretory dysfunction (GHNSD) [n = 21 (10 M, 11 F); age, 25.1+/-1.6 yr; GH peak10 microg/L after classical test but mGHc3 microg/L]. The GH responses to GHRH+ARG in these groups were also compared with that recorded in a group of age-matched normal subjects (NS) [n = 48 (20 M, 28 F); age, 27.7+/-0.8 yr]. Insulin-like growth factor I levels in oGHD subjects (61.5+/-13.7 microg/L) were lower (P0.001) than those in iGHD subjects (117.2+/-13.1 microg/L); the latter were lower than those in GHNSD subjects (210.2+/-12.9 microg/L), which, in turn, were similar to those in NS (220.9+/-7.1 microg/L). The mean GH peak after GHRH+ARG in oGHD (2.8+/-0.8 microg/L) was lower (P0.001) than that in iGHD (18.6+/-4.7 microg/L), which, in turn, was clearly lower (P0.001) than that in GHNSD (31.3+/-1.6 microg/L). The GH response in GHNSD was lower than that in NS (65.9+/-5.5 microg/L), but this difference did not attain statistical significance. With respect to the 3rd centile limit of GH response in young adults (i.e. 16.5 microg/L), retesting confirmed GHD in all oGHD, in 65.2% of iGHD, and in none of the GHNSD subjects. With respect to the 1st centile limit of GH response (i.e. 9.0 microg/L), retesting demonstrated severe GHD in 94% oGHD and in 52.1% of iGHD. All oGHD and iGHD with GH peak after GHRH+ARG lower than 9 microg/L had also GH peak lower than 3 microg/L after ITT. In the patients in whom GHD was confirmed by retesting, the mean GH peak after GHRH+ARG was higher than that after ITT (3.4+/-0.5 vs. 1.9+/-0.4). In conclusion, given appropriate cut-off limits, GHRH+ARG is as reliable as ITT for retesting patients who had undergone GH treatment in childhood. Among these patients, severe GHD in adulthood is generally confirmed in oGHD, is frequent in iGHD, but never occurs in GHNSD.

It is widely accepted that IGF-I synthesis and release depend on GH secretion as well as on the nutritional status and vary with age. Based on these premises, after the definition of normal IGF-I levels during lifespan, in a large population of normal subjects of both sexes, our aim was to verify IGF-I levels in large groups of adult patients with GH deficiency or obesity, a condition in which a reduced somatotrope secretion is well known.To this goal, IGF-I levels were assayed after acid-ethanol extraction, in 326 normal subjects (NS, 98 men and 228 women, age 20-80 yrs, BMI 17.9-26.1 kg/m2), 54 patients with GH deficiency (GHD, 24 men and 30 women, age 20-80 yrs, BMI 18.2-27.1 kg/m2), and 195 patients with obesity (OB, 33 men and 162 women, age 17-71 yrs, BMI 27.7-64.9 kg/m2). In NS, IGF-I levels were similar in both sexes and showed a progressive decrease with age. No correlation was present between IGF-I and BMI in NS. Median IGF-I levels and the 3rd centile in NS when considered per decade were: III) 230 and 108.6; IV) 220 and 129.8; V) 150.5 and 72.4; VI) 163.0 and 62.4; VII) 110 and 41.6; VIII) 82 and 24.7 micrograms/l. In GHD, IGF-I levels were independent on sex and did not show reduction during lifespan. Mean IGF-I levels in GHD were lower than that in NS (64.5 +/- 5.9 vs 171.3 +/- 4.8 micrograms/l, p0.01) and did not correlate with age or BMI. Analyzing individual IGF-I levels, in GHD, in the III and IV decade 21/24 patients had IGF-I levels lower than 3rd centile while, up to the VIII decade, only 10/30 had IGF-I levels below normal limits. In OB, IGF-I levels were independent on sex but, like in NS, showed a progressive decrease with age and were independently, negatively correlated with BMI but not with WHR. Analyzing individual IGF-I levels, in OB, IGF-I levels were below 3rd centile in 10/77 patients in the III and IV decade and in only 8/108 patients up to the VIII decade. Mean IGF-I levels in the whole OB population (179.6 +/- 5.9 micrograms/l) were higher (p0.01) than those in GHD (64.5 +/- 5.9 micrograms/l) while only in the IV decade IGF-I levels in OB group were lower (p0.02) than those in NS (184.7 +/- 12.6 micrograms/l vs 224.0 +/- 9.2 micrograms/l).In conclusion, present data confirm that IGF-I levels depends on GH secretion as well as on nutritional status, being negatively and independently correlated with age and BMI. IGF-I assay is not a reliable test for the diagnosis of GH deficiency in adulthood though it gives good discrimination between GHD and normal subjects up to 40 yrs of age. In spite of low GH secretion, IGF-I levels are only slightly reduced in obesity, probably as consequence of hyperinsulinism.

Growth hormone-releasing peptides (GHRPs) are synthetic, non-natural peptides endowed with potent stimulatory effects on somatotrope secretion in animals and humans. They have no structural homology with GHRH and act via specific receptors present either at the pituitary or the hypothalamic level both in animals and in humans. The GHRP receptor has recently been cloned and, interestingly, it does not show sequence homology with other G-protein-coupled receptors known so far. This evidence strongly suggests the existence of a natural GHRP-like ligand which, however, has not yet been found. The mechanisms underlying the GHRP effect are still unclear. At present, several data favor the hypothesis that GHRPs could act by counteracting somatostatinergic activity both at the pituitary and the hypothalamic level and/or, at least partially, via a GHRH-mediated mechanism. However, the possibility that GHRPs act via an unknown hypothalamic factor (U factor) is still open. GHRP-6 was the first hexapeptide to be extensively studied in humans. More recently, a heptapeptide, GHRP-1, and two other hexapeptides, GHRP-2 and Hexarelin, have been synthesized and are now available for human studies. Moreover, non-peptidyl GHRP mimetics have been developed which act via GHRP receptors and their effects have been clearly demonstrated in animals and in humans in vivo. Among non-peptidyl GHRPs, MK-0677 seems the most interesting molecule. The GH-releasing activity of GHRPs is marked and dose-related after intravenous, subcutaneous, intranasal and even oral administration. The effect of GHRPs is reproducible and undergoes partial desensitization, more during continuous infusion, less during intermittent administration; in fact, prolonged administration of GHRPs increases IGF-I levels both in animals and in humans. The GH-releasing effect of GHRPs does not depend on sex but undergoes age-related variations. It increases from birth to puberty, persists at a similar level in adulthood and decreases thereafter. By the sixth decade of life, the activity of GHRPs is reduced but it is still marked and higher than that of GHRH. The GH-releasing activity of GHRPs is synergistic with that of GHRH, is not affected by opioid receptor antagonists, such as naloxone, and is only blunted by inhibitory influences, including neurotransmitters, glucose, free fatty acids, glucocorticoids, recombinant human GH and even exogenous somatostatin, which are known to almost abolish the effect of GHRH. GHRPs maintain their GH-releasing effect in somatotrope hypersecretory states such as in acromegaly, anorexia nervosa and hyperthyroidism. On the other hand, their good GH-releasing activity has been shown in some but not in other somatotrope hyposecretory states. In fact, reduced GH responses after GHRP administration have been reported in idiopathic GH deficiency as well as in idiopathic short stature, in obesity and in hypothyroidism, while in patients with pituitary stalk disconnection or Cushing's syndrome the somatotrope responsiveness to GHRPs is almost absent. In short children an increase in height velocity has also been reported during chronic GHRP treatment. Thus, based on their marked GH-releasing effect even after oral administration, GHRPs offer their own clinical usefulness for treatment of some GH hyposecretory states. European Journal of Endocrinology 136 445–460

Growth hormone (GH), Insulin Growth Factor-I (IGF-I) and lipids are linked by important reciprocal influences. Their knowledge allowed relevant pathophysiological and clinical acquisitions more and more interesting in scientific research and in medical practice. In this survey the influence of (GH) on lipid metabolism, particularly on free fatty acids (FFA) and lypoprotein metabolism has been analysed. Attention has been given to the disorders of the lipid-metabolism in GH hypo- and hyper-secretory states. On the other hand the role of lipids in the control of GH secretion has been extensively considered with particular attention to the role of exaggerated FFA levels in the pathogenesis of GH insufficiency in obesity.

Bellone J. Aimaretti G, Valetto MR, Bellone S, Baffoni C, Arvat E, Seminara S, Camanni F, Ghigo E, Acute administration of recombinant human growth hormone inhibits the somatotrope responsiveness to growth hormone-releasing hormone in childhood. Eur J Endocrinol 1996:135: 421–4. ISSN 0804–4643 In adulthood the growth hormone (GH) response to growth hormone-releasing hormone (GHRH) is inhibited by previous acute administration of either GH or GHRH and it is restored by substances that inhibit hypothalamic somatostatin release. Because in children the GH response to GHRH is not affected by previous neurohormone administration, it has been suggested that in childhood a GH increase is not able to trigger the somatostatin-mediated negative GH autofeedback mechanism. To verify this hypothesis, in 25 children (8 girls and 17 boys; 15 prepubertal and 10 in pubertal stages II–IV) with familial short stature (normal height velocity and insulin-like growth factor I levels) we studied the effect of acute iv administration of different recombinant human GH doses (group 1, N = 5, 0.06U/kg; group 2, N = 6, 0.01 U/kg; group 3, N = 7, 0.005 U/kg at −150 min or saline on the GH response to GHRH (1 μg/kg iv at 0 min). In another group (N = 7), we studied the effect of 0.005 U/kg iv recombinant human GH or saline on the GH response to GHRH combined with arginine (0.5 g/kg iv over 30 min), which likely inhibits hypothalamic somatostatin release. Serum GH increases after recombinant human GH were dose-dependent (GH peak, mean±sem, 171.7 ± 24.4, 33.3 ± 3.9 and 21.8 ± 5.1 μg/l, respectively). The administration of recombinant human GH strongly inhibited the GHRH-induced GH rise in all groups (group 1, 7.1 ± 1.7 vs 23.1 ± 7.6 μg/l, p < 0.05; group 2, 9.5 ±2.8 vs 26.9±8.5 μg/l, p < 0.05; group 3, 9.1 ±2.7 vs 34.8 ± 7.2 μg/l, p< 0.02). The GH response to arginine + GHRH (56.9 ± 13.3 μg/l) was higher than that to GHRH alone recorded in group 1 (p < 0.005), group 2 (p < 0.01) and group 3 (p < 0.01), while exogenous recombinant human GH failed to inhibit it (45.0 ± 9.4 μg/l). Our results demonstrate that in childhood, as well as in adulthood, recombinant human GH administration inhibits the somatotrope responsiveness to GHRH. This inhibitory effect is likely to be mediated by hypothalamic somatostatin release. Ezio Ghigo, Divisione di Endocrinologia, Ospedale Molinette, C.so Dogliotti 14, 10126 Torino, Italy

The aim of this work was to clarify the mechanisms underlying growth hormone (GH) hyposecretion in Cushing's syndrome (CS) and in obesity. We studied the GH response to GH-releasing hormone (GHRH) alone and combined with arginine or pyridostigmine, two substances likely to inhibit hypothalamic somatostatin release.Three tests with GHRH alone (1 microgram/kg i.v. at 0 min) and combined with arginine (ARG, 0.5 g/kg infused over 30 min) or pyridostigmine (PD, 120 mg orally at -60 min) were performed 3 days apart and in random order in eight women with CS (five with ACTH-dependent and three with ACTH-independent hypercortisolism, age 18-56, BMI 26.1 +/- 1.5 Kg/m2) and 11 with OB (age 17-54, BMI 42.9 +/- 2.2 Kg/m2). Eleven normal women (age 23-50, BMI 21.9 +/- 0.3 Kg/m2) were studied as controls (C).Serum GH and IGF-I levels were measured by radioimmunoassay. The GH secretory responses were expressed either as absolute values (micrograms/L) or as areas under the curve (AUC, micrograms/L/h) calculated by trapezoidal integration. IGF-I concentrations were expressed as absolute values (micrograms/L) with reference to a pure recombinant IGF-I preparation.Basal GH levels in CS were similar to those registered in OB (mean +/- s.e.m. 0.7 +/- 0.1 vs 0.9 +/- 0.2 microgram/L) and lower than in C (3.4 +/- 0.5 microgram/L, P0.00001). On the other hand, IGF-I levels were similar in all groups. The GHRH-induced GH rise in CS was lower, though not significantly, to that observed in OB (AUC: 65.6 +/- 13.2 vs 192.5 +/- 61.7 microgram/L/h) and both GH responses were significantly lower than that of C (1029.9 +/- 98.0 micrograms/L/h, P0.00001). ARG enhanced the GHRH-induced GH release in CS (331.9 +/- 51.9 micrograms/L/h vs GHRH alone, P0.0001), OB (852.4 +/- 162.1 micrograms/L/h, P0.0001) and C (3362.6 +/- 386.0 micrograms/L/h, P0.0002). However, the GH response to GHRH plus ARG in CS was lower (P0.002) than that in OB which, in turn, was lower than that in C (P0.00001). Pyridostigmine significantly enhanced the GHRH-induced GH rise in C (2808.5 +/- 221.2 micrograms/L/h, P0.00001) and, to a lesser extent, in OB (627.3 +/- 84.7 micrograms/L/h, P0.0002) but not in CS (102.9 +/- 25.0 micrograms/L/h).Our results indicate that the GH releasable pool is reduced in obesity and, to an even greater extent, in Cushing's syndrome. The inability of pyridostigmine and arginine to restore a normal GH response to GHRH in these conditions makes the existence of a hypothalamic somatostatinergic hyperactivity unlikely.

Summary OBJECTIVE A new long-acting injectable form of bromocriptine has become available for long-term treatment of hyperprolactinaemic patients. The objective of this study was to compare efficacy and tolerability of injectable and oral forms of bromocriptine. DESIGN A double-blind randomized study. All patients received either one injection of bromocriptine 50 mg intramuscularly and placebo tablets for 28 days (Group A) or one placebo injection and oral bromocriptine 7 5 mg daily for 28 days (Group B). PATIENTS Twenty-three (12 patients for Group A and 11 patients for Group B) hyperprolactinaemia patients with (19 patients) or without (4 patients) CT/MRI evidence of tumour were studied. MEASUREMENTS Plasma PRL levels and serum bromocriptine levels were assessed during a follow-up of 42 days. MRI and/or CT were evaluated before and 28 days after the beginning of the study. RESULTS All patients had significant reductions of PRL levels from 1000 h and 1100 h of day 1 to 2000 h of day 35. Normoprolactinaemia was shown in eight patients of Group A and six of Group B on days 1-28. Normal PRL levels were still present in five patients of Group A and in one patient of Group B on day 35; only three patients of Group A had normoprolactinaemia on day 42. A significantly greater decrease in Group A in comparison with Group B was shown at 1200 h on day 1 and at all times as a percentage decrease from basal levels. Significantly higher levels of bromocriptine were shown in Group A at all timepoints studied. No difference was shown in tolerability and incidence of side-effects. CONCLUSION Our data show that injectable bromocriptine more frequently induced a prolonged normoprolactinaemia than did the oral drug. Moreover, bromocriptine levels released during injectable bromocriptine were significantly higher than during oral bromocriptine. On the other hand no difference was shown in the tolerability of bromocriptine according to the route of administration.

Reportedly, the responsiveness of somatotrope cells to GHRH is reduced in elderly humans but it is totally restored by arginine (ARG) which likely acts by inhibiting hypothalamic release of somatostatin. As this effect was observed after infusion of high doses of the amino acid, in this study, we compared the effect of iv administration of 30, 10 and 5 g ARG(group A, B and C, respectively) as well as oral administration of 8 g ARG(group D) on the GH response to 1 microgram/kg i.v.GHRH in 27 healthy elderly subjects (11 M and 16 F, age 70-86 yr, BMI 21-25 kg/m2). In group A (n = 7) 30 g i.v. ARG strikingly enhanced the GHRH-induced GH rise (peak, mean +/- SE: 41.5 +/- 4.4 vs 11.7 +/- 5.3 micrograms/L, p < 0.05). Similarly, in group B (n = 6) and D (n = 7) 10 g i.v. and 8 g oral ARG enhanced the GH response to GHRH (20.9 +/- 4.7 vs 8.3 +/- 2.8 micrograms/L, p < 0.03 and 31.0 +/- 5.3 vs 11.4 +/- 3.4 micrograms/L, p < 0.03, respectively). In contrast, in group C (n = 7) 5 g i.v. ARG failed to modify the GHRH-induced GH rise (6.0 +/- 1.6 vs 3.5 +/- 0.9 micrograms/L). The GH responses to GHRH alone did not significantly differ amongst groups; the GH responses to GHRH and ARG were not significantly different among groups A, B and D and were greater than the GH response in group C. These results show that the GH response to GHRH in elderly subjects is enhanced even by low iv doses of arginine and by the orally administered amino acid, the lowest effective dose being 8 g. Moreover, they imply that the combined administration of GHRH and arginine may be a useful approach to restore the impaired function of the GH-IGF axis in aging.

It is widely accepted that growth hormone (GH) secretion undergoes an age-related decrease in both animals and humans (Dieguez et al. 1988 Muller and Nistico 1989). Twenty-four-hour integrated GH concentrations have been shown to be lower in older versus younger subjects (Zadik et al. 1985). More recently, the study of the 24-h GH profile with frequent sampling techniques demonstrated that both day-time and night-time mean pulse amplitude and duration but not pulse frequency are reduced in aged humans (Vermeulen 1987; Van Coervorden et al. 1991). On the contrary, other authors (Iranmanesh et al. 1991) found significant reductions in GH secretory burst frequency and half-life but not in GH secretory burst half duration, amplitude or mass. Interestingly, though both slow wave sleep and nocturnal GH secretion are drastically reduced in the elderly, the small GH rises during sleep are nevertheless temporally related to slow wave stages (Van Coervorden et al. 1991).

It is well known that in normal adults the growth hormone (GH) response to GH-releasing hormone (GHRH) is inhibited by previous administration of the neurohormone. In 7 healthy volunteers (age 20-34 years) we studied the GH responses to two consecutive GHRH boluses (1 microgram/kg i.v. every 120 min) alone or coadministered with arginine (30 g i.v. over 30 min). The GH response to the first GHRH bolus (area under the curve, mean +/- SEM: 506.3 +/- 35.1 micrograms/l/h) was higher (p = 0.0001) than that to the second one (87.1 +/- 14.6 micrograms/l/h). The latter response was clearly increased (p = 0.0001) by coadministering arginine (980.5 +/- 257.5 micrograms/l/h). When every GHRH bolus was combined with arginine a marked potentiation of GH response to both boluses was found. However, the second combined administration of arginine and GHRH induced a GH increase which was lower compared to the first one (p = 0.016). In conclusion, our results show that arginine potentiates the GHRH-induced GH secretion preventing the lessening of somatotrope responsiveness to the neurohormone alone. As there is evidence that this phenomenon is due to an enhanced somatostatin release, these findings give further evidence of a somatostatin-suppressing effect of arginine.

The adrenergic system is involved in the neural control of GH secretion with both stimulatory and inhibitory influences mainly mediated via GHRH and/or somatostatin modulation. To throw further light on adrenergic neuroregulation of somatotrophic function in man, the effect of various catecholamine agonists and antagonists on basal or GHRH-stimulated GH secretion was studied. Twenty-one adult males aged 20-30 years underwent the following studies: 1. clonidine (CLON), alpha 2-agonist, (15 micrograms/min infused i.v. from 0 to +10 min) alone and preceded by yohimbine (YOH), alpha 2-antagonist, (30 mg orally at -50 min); 2. GHRH (GHRH 44, 1 microgram/kg i.v. bolus at 0 min) alone and preceded by YOH; 3. CLON alone and combined with methoxamine (METHOX), alpha 1-agonist, (1 mg/min infused i.v. from -10 to +10 min); 4. GHRH alone and combined with i.v. infusion of phentolamine (PHEN), alpha 1/alpha 2-antagonist, (0.5 mg/min from -60 to +30 min); 5. GHRH alone and combined with i.v. infusion of salbutamol (SAL), beta 2-agonist, (10 micrograms/min from -5 to +15 min). The GH response to CLON was inhibited by YOH (area under the response curve, mean +/- S.E.: 672.6 +/- 143.0 vs. 219.6 +/- 16.7 micrograms/l/h, P less than 0.05) but was not modified by METHOX (278.4 +/- 94.1 vs. 216.7 +/- 115.5 micrograms/l/h). On the other hand, YOH was unable to affect the GH response to GHRH (339.3 +/- 19.1 vs. 518 +/- 172.8 micrograms/l/h).(ABSTRACT TRUNCATED AT 250 WORDS)

Thirty acromegalic subjects underwent chronic CB154 therapy (10–20 mg daily) for periods ranging from 3 months up to 2 years. In 18 out of 21 patients, who exhibited consistent HGH reduction following acute administration of the drug, there was also during chronic treatment, a suppression of the plasma HGH levels exceeding 50 % of base line values, e.g. from mean daily values between 14–197 ng/ml (mean ± sem = 57.8 ± 12.4 ng/ml pre-treatment) to 2–19 ng/ml (mean 8.3 ± 1.2 ng/ml post-treatment). In 12 of the subjects who responsed to chronic CB154 treatment, the mean daily values of HGH were below 10 ng/ml. The suppression of plasma HGH was maintained unaltered throughout the whole course of therapy. In the 9 subjects, in whom no consistent HGH decrease was evidenced with acute CB154 administration, there was accordingly a minor or no suppression of HGH values during the chronic treatment. In 13 subjects, irrespective of the degree of their GH responses, the plasma prolactin levels were constantly inhibited by CB154; instead the drug failed to modify significantly the TRH or insulin-induced GH release. These changes in the hormonal parameters were paralleled by marked clinical amelioration and improvement of some of the metabolic alterations frequently encountered in acromegaly, e.g. reduced carbohydrate tolerance, increased insulin resistance, diminished fall of plasma phosphorus after insulin, decreased urinary excretion of phosphate, hyper hydroxyprolinuria and hyper-calciuria. Collectively, these data demonstrate that CB154 thrapy is effective in reducing HGH hyper-secretion in many acromegalic patients during long-term treatment.

A study on steroid hormone metabolism in 24 cases of blood dyscrasias has been performed through chemical determination of urinary 17-ketosteroids and 17-hydroxycorticosteroids and chromatographic analysis of the former. Corticoids appeared to be preferentially decreased in acute leukemia, chronic myelogenous leukemia and polycythemia, while in chronic lymphatic leukemia and in Waldenstrom's disease 17-ketosteroids were affected as well. The chromatographic analysis of 17-ketosteroids showed that fractions IV and V, corresponding to androsterone and etiocholanolone, are decreased in almost all cases. High and bifid peaks III are constantly found in polycythemia and haemophilia; changes of peak III of a minor importance are occasionally found in all types of leukemia. The significance of the data observed is discussed from the point of view of steroid metabolism and a hypothesis is presented to explain the mechanism of the changes occurring in pattern of the various chromatographic fractions of 17-ketosteroids.

SUMMARY The effects of various adrenergic substances, either alone or in association with alpha and beta blocking agents, on human plasma growth hormone (GH) were studied in 36 normal volunteers. Plasma GH levels were unaffected by i.v. adrenaline (10 μg/min for 30 min) or by propranolol (1·5 mg/min for 10 min). Given together at the same doses, these drugs provoked sharp increases in plasma GH (from 8·5 to > 100 ng/ml; a mean increase of 30±8·02 (s.e.m.)). Reduction of the adrenaline dose to 7 μg/min produced a positive response in four out of six cases. The GH response to propranolol plus adrenaline was suppressed by simultaneous administration of phentolamine, but not significantly altered by glucose and aminophylline. Noradrenaline (7–14 μg/min for 30 min) produced no changes in plasma GH levels in six cases, while its association with propranolol was followed by an increase in only one out of four cases. Phenylephrine and tyramine were without effect, with or without propranolol. In five out of six cases, GH values gradually increased after oral administration of 1 g l-DOPA (from 4·2 to 85 ng/ml; mean, 30·2). This response was totally suppressed by phentolamine. It is considered that stimulation of GH by propranolol plus adrenaline and l-DOPA is mediated by alpha-adrenergic receptors. The possible role of a beta-inhibiting effect is discussed.

SUMMARY A study has been made of the inorganic serum phosphorus pattern in twenty-one acromegalic subjects during the 'augmented insulin tolerance test'. The serum phosphorus curve differed from normal in an elevated fasting level and, more especially, a reduction in the maximum fall. The latter anomaly is far more marked and constant than those found in the blood-sugar curve, and would thus seem to be a reliable criterion for the 'activity' of acromegaly.

An attempt was made to determine whether 6α-methyl-17α-acetoxyprogesterone (MAP) was as active as a glucocorticoid in man, as in experimental animals. This steroid was administered as a substitute for cortisone to 5 patients with definite signs of adrenal insufficiency. The subcutaneous administration of MAP in doses of 100 mg per day caused the prompt and complete disappearance of the symptoms attributable to glucocorticoid insufficiency which had developed when cortisone had been replaced by 9α-fluoro-hydrocortisone. When substitution treatment was carried out with MAP only, compensation was practically the same as with the daily administration of 50 mg cortisone. The glucose-tolerance and the insulin tests demonstrated that MAP administered subcutaneously displayed a marked glycogenetic activity.

The effect of propranolol on certain insulin-induced metabolic changes in man. The effects of 0.2 mg/kg/body weight propranolol perfused in 10' on insulin-induced (0.15 I.U./Kg i.v.)changes in blood glucose, pyruvate, lactic acid, phosphorus, and potassium levels were examined in 12 normal volunteers. The blood glucose curve was substantially unaffected. Insulin-induced increases in lactate and pyruvate were inhibited to a varying degree, namely 78% (61-93%) and 44% (0.94%) respectively. The fall in phosphorus was reduced in a more constant manner (mean 48; range 37-57%) in all subjects, while that of potassium was not altered. The data indicate that these insulin-induced changes are significantly, though variably, attributable to beta-adrenergic activity on the part of endogenous catecholamines released during insulin-induced hypoglycaemia.

To verify the diagnostic capacity of some dynamic tests of the prolactin (Prl) secretion, the findings obtained by high-resolution computed tomography (CT) were compared with results obtained from tests using nomifensine (NOM) domperidone (DOM) and thyrotrophin-releasing hormone (TRH) in 72 patients with pathological hyperprolactinaemia. None of the patients with tumours had a positive Prl response to NOM or to DOM administration; however, a positive response to these tests was present in only 24 and 41%, respectively, of the patients with normal CT picture. The results of TRH testing were similar to those obtained with DOM. Different neuroendocrine patterns were disclosed by comparing pituitary Prl and thyrotrophin (TSH) responses to DOM: 1) some subjects had a reduced Prl response together with an exaggerated or normal TSH response to DOM; they comprised patients with tumour, empty sella, and normal CT picture; 2) other patients with normal CT picture had a positive Prl and a normal TSH response to DOM. These results demonstrate that a negative Fri response to NOM and DOM characterizes all patients with adenoma; however, the tumour-like responses in patients with no visible tumours seem to reduce the diagnostic value of these tests, unless the latter may predate the radiological appearance of an adenoma. On the other hand, a positive Prl and a normal TSH response to DOM exclude the presence of a pituitary tumour. This diagnostic finding is strengthened by the positive response also to NOM. Whatever may be the diagnostic validity of dynamic tests, they provide sound information on the functional state of dopamine neurotransmission.

The prolactin (PRL)-releasing effect of domperidone (DOM), a novel antidopaminergic drug which does not cross the blood-brain barrier, was investigated in normoprolactinemic subjects, in subjects with physiologic puerperal hyperprolactinemia or pathological hyperprolactinemia. DOM (4 mg i.v.), administered to 8 normoprolactinemic women, induced a clear-cut and sustained rise in plasma PRL, with peak levels occurring 15-30 min postinjection; the effect of the drug was also evident in 3 normoprolactinemic women at the dose of 0.25 mg i.v. Also in 8 puerperal women (postpartum day 2) intravenous administration of 4 mg DOM was followed by an increase in plasma PRL (51-517% of baseline levels, 15-45 min postinjection). Administration of DOM (4 mg i.v.) to 16 subjects with pathological hyperprolactinemia, evidenced the presence of 14 DOM-nonresponder (maximum percent increase of baseline PRL 48%) and 2 DOM-responder subjects. In 8 of the DOM-nonresponder subjects the existence of a pituitary tumor was established at surgery by selective removal of an adenoma (7 subjects) or a teratoma (1 subject): of the 6 subjects who did not undergo surgery, 3 had biochemical and/or radiologic evidence suggestive of a PRL-secreting tumor and 1 was acromegalic. These results indicate that DOM is capable of releasing PRL both in normoprolactinemic subjects and subjects with puerperal hyperprolactinemia. In contrast, DOM is unable to modify PRL levels in most subjects with pathological hyperprolactinemia, with proven or suspected pituitary tumors.

It is now a tenet of neuroendocrinology that the secretion of anterior pituitary (AP) hormones is regulated by the central nervous system (CNS) through a family of hypophysiotropic neuropeptides, the releasing and inhibiting hormones. In addition, the neuroregulation of a given AP hormone is influenced by a host of neurotransmitters and neuropeptides, which at hypothalamic and suprahypothalamic levels provide intermediate and obligatory links between hypophysiotropic and both exogenous and endogenous influences on hormone secretion (1,2), Figure 1 depicts schematically how neurotransmitter-neurohormonal interactions may occur at the hypothalamic level. The complexity of the system stems from the abundance of different neurotransmitter and neuropeptide neurons present in the mediobasal hypothalamus (MBH) and the various ways they may reciprocally interact. Another reason for complexity is the phenomenon of coexistence, which ultimately results from cotransmission, i.e., occurrence and then release of two transmitter substances present in the same nerve endings (3). Though cotransmission undoubtedly provides greater versatility and sophistication to the vocabulary of synaptic transmission (3), it compounds the understanding of the physiology and pathophysiology of neuroendocrine control.

The involvement of the cholinergic system in GH secretion has recently acquired increasing importance. Data have been presented suggesting that in rats the effect of cholinergic modulation on GH secretion takes place through inhibition or stimulation of hypothalamic somatostatin (SRIF) release. To investigate further the significance of cholinergic-SRIF link and its role in the regulation of GH secretion, the action of cholinergic agonist and antagonist drugs in the GH short-loop feedback mechanism mediated by SRIF was investigated. Intracerebroventricular (i.c.v.) infusion of 0·2 or 2·0 μg GH/rat into the lateral brain ventricle of adult male rats induced a significant reduction in the GH-releasing hormone (GHRH; 2 μg/kg, i.v.)-induced peak GH rise, but only the 2·0 μg dose reduced also the GH-integrated area after administration of GHRH. This effect was absent after central administration of 20·0μg GH/rat, due probably to leakage of some GH from the cerebral ventricle into the systemic circulation. Pretreatment with cysteamine (300 mg/kg, s.c.), a known depletor of hypothalamic SRIF, or with anti-SRIF serum (0·5 ml/rat) completely counteracted the lessening of the GH response to GHRH induced by 2·0μg GH injected i.c.v. Similarly, pretreatment with the cholinergic agonist pilocarpine (3 mg/kg, i.v.) completely antagonized the inhibitory effect of central infusion of GH on the GHRH-induced GH response. Atropine (1·0 mg/kg, i.v.), a muscarinic cholinergic antagonist, strikingly inhibited the GHRH-induced GH rise, but when given in combination with i.c.v. infusion of GH there was no additive inhibitory effect. These data reinforce the idea that the GH autofeedback triggered by i.c.v. infusion of GH is mediated by enhanced SRIF release, and suggest that the hypothalamic cholinergic system plays a major role in this mechanism. J. Endocr. (1988) 117, 273–281

A new long-acting repeatable injectable form of bromocriptine, (Parlodel LAR, Sandoz, Basle, Switzerland) has recently been developed. We studied the clinical, hormonal and radiological changes in six female patients with microprolactinomas and eight (3 female and 5 male) with macroprolactinomas receiving monthly injections of Parlodel LAR 50 to 100 mg for 6 months. Five patients with microadenomas and 4 with macroadenomas had normal prolactin (PRL) levels with Parlodel LAR 50 mg after one (5 patients), two (2 patients), or five (2 patients) injections; two patients with macroadenomas had normal or near normal PRL levels only after 4 monthly injections of 100 mg. Clinical improvement paralleled the changes in serum PRL. A complete normalization of a visual field defect occurred in one patient after 5 months of therapy. Marked shrinkage of the adenoma was shown by magnetic resonance and/or computed tomographical imaging in three patients with macroadenomas after 1 week. Side-effects were mild and usually transient. Parlodel LAR represents a novel treatment of hyperprolactinemic states which is both effective and well tolerated, and appears to be a useful alternative to oral therapy for long-term treatment.

The effect of 100 mg im sulpiride on plasma Prl levels was studied in 10 normal females, 21 patients with galactorrhoea and normal plasma Prl, 10 women with puerperal hyperprolactinaemia and 27 patients with amenorrhoea-galactorrhoea and high plasma Prl levels. The response to sulpiride in patients with galactorrhoea but normal Prl was slightly higher (P < 0.05) than that observed in normal women, but only if expressed in per cent. Women with puerperal hyperprolactinaemia respond to the drug with a marked increase in Prl (mean ± sem: 563.0 ± 142.8%), even though their baseline values are already very high (mean ± sem: 133.6 ± 23.8 ng/ml). By contrast, there is a lower or no response to sulpiride in 13 women with pituitary tumour. The same was true in 11 patients with hyperprolactinaemia of uncertain aetiology but also 10 of these subjects presented signs suggestive of a tumour. In the last 3 patients with pathological hyperprolactinaemia in whom a consistent Prl increase after sulpiride was observed, hyperprolactinaemia was probably not of tumourous origin. On the basis of these results, the sulpiride test appears promising for discriminating between organic and 'functional' cases of enhanced Prl secretion.

The effect on plasma prolactin (PRL) of two indirectly acting DA agonists (IADA), i.e., methylphenidate and amineptine was studied in normo- and hyperprolactinemic subjects. PRL responses to methylphenidate and amineptine were compared to those previously obtained with the use of another IADA, namely, nomifensine. In normoprolactinemic women methylphenidate (20 mg, orally) or amineptine (200 mg, orally) induced a significant decrease in baseline PRL (maximal change from baseline 50% at 90 min), a pattern reminiscent of that induced by nomifensine (maximal change from baseline 35% at 120 min). Likewise, in puerperal women (postpartum day 2) methylphenidate and amineptine induced a clear-cut lowering of baseline PRL (40% inhibition at 90 min and 180 min, respectively); nomifensine induced 60% inhibition of resting PRL levels at 150 min. In subjects with pathological hyperprolactinemia (proven or highly probable PRL-secreting tumor or uncertain etiology), previously shown to be unresponsive to the PRL-lowering effect of nomifensine, methylphenidate or amineptine did not significantly lower baseline PRL (maximal change from baseline 8% at 150 min and 3% at 90 min, respectively). In few of these subjects methylphenidate and amineptine failed to lower plasma PRL levels also at doses of 30 and 300 mg, orally, respectively. These data indicate that (1) two other IADA, i.e., methylphenidate and amineptine, are effective PRL-lowering agents in both normoprolactinemic and puerperal subjects, whereas they are unable to lower plasma PRL in patients with proven or probable PRL-secreting tumors; (2) the ability of the different drugs to inhibit plasma PRL in puerperal versus pathological hyperprolactinemia emphasizes the different tuberoinfundibular DA (TIDA) neurotransmission present in the two clinical conditions; (3) in view of the mechanism of action of the IADA, there is a defect in TIDA metabolism or transport in patients harboring a prolactinoma.

SUMMARY The TSH and PRL responses to administration of the two dopamine (DA) receptor antagonists sulpiride and domperidone, were studied in fifteen normoprolactinaemic subjects, twenty-two post-partum women and sixteen subjects with presumptive evidence of (six subjects) or surgically confirmed (ten subjects) prolactinomas. Sulpiride (100 mg i.m.) or domperidone (10 mg i.v.) elicited a slight increase in basal TSH levels in both normoprolactinaemic and post-partum women, but induced a clear-cut TSH rise in subjects with a tumour. Conversely, sulpiride and domperidone strikingly stimulated PRL secretion in normoprolactinaemic and post-partum women, but only slightly enhanced base-line PRL levels in women with prolactinomas. The reason for the reciprocal pattern of TSH and PRL responsiveness to DA receptor blockade of post-partum women and subjects with prolactinomas is presently obscure. Since baseline PRL levels in the two hyperprolactinaemic states overlapped widely, it would appear that hyperprolactinaemia per se is not responsible for such behaviour.