GH-independent cardiotropic activities of hexarelin in patients with severe left ventricular dysfunction due to dilated and ischemic cardiomyopathy.

AIM: To investigate acute cardiotropic activities of hexarelin in patients with severe left ventricular dysfunction due to ischemic (iCMP) and dilated cardiomyopathy (dCMP). METHODS AND RESULTS: We studied the effect of intravenous hexarelin administration on growth hormone (GH) levels and left ventricular ejection fraction (LVEF) evaluated by radionuclide angiography in eight patients with dCMP (age 53.0+/-2.8, LVEF 16.7+/-2.1%) and five patients with iCMP (age 52.0+/-2.8 years, LVEF 22.6+/-2.1). Results were compared with a group of seven normal subjects (age 37.4+/-3.4 years, LVEF 64.0+/-1.5%) and seven patients with severe growth-hormone deficiency (GHD; age 42.0+/-4.4 years, LVEF 50.0+/-1.9%) previously studied with the same methodology. In dCMP and iCMP patients hexarelin induced a similar significant (P<0.05) increase in GH levels. In iCMP patients hexarelin induced a LVEF increase (peak LVEF 26.2+/-2.5%, P<0.05) as observed in normals and GHD, while in dCMP LVEF was unchanged (peak LVEF 17.7+/-1.7, P=NS). In all groups other hemodynamic parameters were unchanged. CONCLUSIONS: Acute hexarelin administration increases LVEF in iCMP patients (as in normals and GHD) but not in dCMP patients in spite of a similar GH releasing effect and basal LVEF. A possible explanation of the positive inotropic effect of hexarelin in iCMP could be a direct stimulation on viable myocardium or myocardial contractile reserve.

Growth hormone-independent cardiotropic activities of growth hormone-releasing peptides in normal subjects, in patients with growth hormone deficiency, and in patients with idiopathic or ischemic dilated cardiomyopathy.

Growth hormone releasing peptides (GHRPs) are synthetic molecules endowed with potent neuroendocrine activities mediated by specific receptors in the pituitary and in the central nervous system. GHRPs receptors have been reported even in perpheral tissues, particularly in the myocardium, where they probably mediate growth hormone (GH)-independent activities. We studied in humans the cardiac effects of hexarelin administration in 7 normal adults, in 7 severe GH-deficient patients, and in 12 patients with severe dilated cardiomyopathy. Left ventricular ejection fraction (LVEF), mean blood pressure (MBP), heart rate (HR), and GH levels were evaluated at baseline and every 15 min up to 60 min after acute 2.0 microg/kg iv hexarelin administration. Basal LVEF in dilated cardiomyopathy was impaired and lower (p < 0.001) than in GH deficiency, in turn lower (p< 0.001) than in normal subjects. Hexarelin signficantly (p < 0.05) increased LVEF in normal and in GH-deficient subjects, but not in dilated cardiomyopathy, without significant variations in MBP and HR. Hexeralin significantly (p < 0.05) increased GH levels in normal subjects and in dilated cardiomyopathy but not in GH deficiency. These findings suggest that, in humans, the acute administration of hexarelin exerts a GH-independent positive inotropic effect likely mediated by specific GHRPs myocardial receptors.

Technetium-99m labelled macroaggregated albumin arterial catheter perfusion scintigraphy: prediction of gastrointestinal toxicity in hepatic arterial chemotherapy.

Gastrointestinal toxicity from hepatic arterial infusion (HAI) of floxuridine in patients with liver metastases is probably due to extrahepatic perfusion or to partial escape of the drug from first-pass liver extraction. The aim of this study was to verify the role of technetium-99m-labelled macroaggregated albumin (99mTc-MAA) arterial catheter perfusion scintigraphy at the beginning of each chemotherapy cycle in decreasing or preventing gastrointestinal toxicity. We studied 167 consecutive patients. On the basis of the scintigraphic follow-up and the presence or absence of an intrahepatic arteriovenous shunt (IHAVS), we classified our patients into the following groups: (1) FU+ hepatic distribution pattern (DP), comprising 29 patients with regular scintigraphic follow-up who showed the expected distribution pattern at each control or a distribution pattern with transient alterations (extrahepatic escape) promptly reversed by the replacement of the catheter. Among these 29 patients there was one case of gastrointestinal toxicity. (2) FU- hepatic DP, comprising 128 patients who were evaluated with 99mTc-MAA only at the beginning of the first chemotherapy cycle, showed the expected distribution pattern and underwent HAI with no further scintigraphic evaluation. Among these 128 patients there were 28 cases of gastrointestinal toxicity. (3) FU+ pulmonary DP, comprising three patients with abnormally elevated pulmonary uptake (higher than 5%) and with regular scintigraphic follow-up. There were two cases of gastrointestinal toxicity among these three patients. (4) FU- pulmonary DP, comprising seven patients with abnormally elevated pulmonary uptake and without regular scintigraphic follow-up. There were four cases of gastrointestinal toxicity among these seven patients. The incidence of toxicity was significantly higher in group FU- hepatic DP than in group FU+ hepatic DP (21.9% vs 3.4%, P<0.05). In both the FU+ pulmonary DP and FU- pulmonary DP groups, the incidence of gastrointestinal toxicity was higher than 50%, with no significant difference between them. We conclude that, when performing 99mTc-MAA perfusion scintigraphy, the presence of an abnormally elevated pulmonary uptake (IHAVS higher than 5%) is the most relevant positive prognostic index for the development of gastrointestinal toxicity. Furthermore, in the absence of abnormal pulmonary uptake (IHAVS lower than 5%), strict scintigraphic follow-up is useful since it is able to promptly diagnose the presence of extrahepatic abdominal perfusion and thus to prevent the occurrence of gastrointestinal toxicity.

Growth hormone-releasing peptides and the cardiovascular system.

Growth Hormone (GH)-releasing peptides (GHRPs) and their non peptidyl analogues are synthetic molecules which exhibit strong, dosedependent and reproducible GH-releasing activity but also significant PRL- and ACTH/cortisol-releasing effects. An influence of these compounds on food intake and sleep pattern has been also shown. The neuroendocrine activities of GHRPs are mediated by specific receptors subtypes that have been identified in the pituitary gland, hypothalamus and various extra-hypothalamic brain regions with (125)I-Tyr-Ala-hexarelin, an octapeptide of the GHRP family. In addition, GHRP receptors were also present in different peripheral tissues such as heart, adrenal, ovary, testis, lung and skeletal muscle, with a density significantly higher than that found in the hypothalamo-pituitary -system. A remarkable specific (125)I-Tyr-Ala-hexarelin binding was observed in the human cardiovascular system where the highest binding levels were detected in ventricles, followed by atria, aorta, coronaries, carotid, endocardium and vena cava. The binding of the radioligand to cardiac membranes was inhibited by unlabeled Tyr Ala hexare lin and hexarelin as well as by GHRP-6, GHRP-1 and GHRP-2 but not by MK-677, a non peptidyl GHRP analog. In other experiments on H9c2 myocytes, a fetal cardiomyocytes-derived cell line, specific GHRP binding was found and hexarelin showed an anti-apoptotic activity. On the other hand, in vivo studies in animals and in humans showed that GHRPs possess direct cardiotropic actions. In fact, hexarelin protects from ischemia-induced myocardial damage in aged and GH deficient rats while hexarelin shows a positive inotropic effect in normal subjects as well as in patients with GH deficiency. In conclusion, GHRPs possess extra--neuroendocrine biological activity and, particularly, show direct GH-independent cardiotropic effects.

The negative GH auto-feedback in childhood: effects of rhGH and/or GHRH on the somatotroph response to GHRH or hexarelin, a peptidyl GH secretagogue, in children.

Aim of the present study was to further clarify the negative GH auto-feedback mechanisms in childhood. To this goal we studied the effects of rhGH and/or GHRH administration on the GH response to GHRH or hexarelin (HEX), a peptidyl GH secretagogue, in normal short children. In 34 prepubertal children (12 girls and 22 boys, age 8.2- 14.2 yr) with normal short stature (normal height velocity and IGF-I levels) the following tests were performed: group A (no.=11): GHRH (GHRH 1 - 29, Geref, Serono; 1 microg/kg iv at 150 min) preceded by saline or GHRH at 0 min; group B (no.=6): GHRH preceded by saline or rhGH (0.005 IU/kg iv at 0 min); group C (no.=6): GHRH preceded by rhGH alone or combined with GHRH; group D (no.=6): HEX (2 microg/kg iv at 150 min) alone or preceded by rhGH. In group A, the GH response to GHRH was not modified by pre-treatment with GHRH (GH peak, mean+/-SEM: 16.7+/-2.9 vs 15.1+/-2.3 microg/l, respectively). In group B, the GH response to GHRH was clearly inhibited by rhGH (8.7+/-2.3 vs 38.8+/-4.5 microg/l, p<0.001); the GH rise after rhGH in group B overlapped with that after GHRH in group A. In group C, the GH response to GHRH after pre-treatment with rhGH (13.2+/-4.0 microg/l) was similar to that in group B and was not significantly modified by pre-treatment with rhGH+ GHRH (6.9+/-2.7 microg/l); the GH rise after rhGH+GHRH was higher (p<0.05) than that after rhGH alone. In group D, the GH response to HEX was significantly blunted by pre-treatment with rhGH (34.1+/-11.7 vs 51.2+/-17.9 microg/l, p<0.05). Our results demonstrate that in childhood the somatotroph response to GHRH is preserved after GHRH while it is inhibited after rhGH administration, which is also able to blunt the GH response to HEX. Thus, the somatostatin-mediated negative GH auto-feedback is already operative in childhood; the reason why the GHRH- induced GH rise is not inhibited by GHRH pre-treatment is unexplained.

Cardiac effects of hexarelin in hypopituitary adults.

Growth hormone (GH)-releasing peptides possess specific pituitary, hypothalamic, and myocardial receptors. Seven adult male patients with GH deficiency (GHD) (age, mean+/-S.E.M.: 42.0+/-4.0 year) were studied by equilibrium radionuclide angiocardiography after i.v. administration of hexarelin, a peptide GH secretagogue. Data for these patients were compared with those for nine adult male controls (37.0+/-2.7 year). The GH response to hexarelin was negligible in patients with GHD compared to control subjects (CS) (peak: 1.9+/-0.9 vs. 45.7+/-3.6 microg/l, P<0.001). Basal left ventricular ejection fraction (LVEF) in patients with GHD was lower than that in CS (50+/-1% vs. 63+/-2%, P<0.001). Hexarelin administration increased LVEF both in patients with GHD and in CS (peak: 57+/-2 vs. 70+/-2, respectively, P<0.05 vs. baseline) without changing catecholamine levels, mean blood pressure (MBP), or cardiac output in either group. In conclusion, the acute administration of hexarelin exerts a short-lasting positive inotropic effect in humans, probably GH-independent and mediated by specific myocardial receptors for GH secretagogues.

Acute cardiovascular and hormonal effects of GH and hexarelin, a synthetic GH-releasing peptide, in humans.

Reduced cardiac mass and performances are present in GH deficiency and are counteracted by rhGH replacement. GH and IGF-I possess specific myocardial receptors and have been reported able to exert an acute inotropic effect. Synthetic GH secretagogues (GHS) possess specific pituitary and hypothalamic but even myocardial receptors. In 7 male volunteers, we studied cardiac performance by radionuclide angiocardiography after iv administration of rhGH or hexarelin (HEX), a peptidyl GHS. The administration of rhGH or HEX increased circulating GH levels to the same extent (AUC: 1594.6+/-88.1 vs 1739.3+/-262.2 microg/l/min for 90 min) while aldosterone and catecholamine levels did not change; HEX, but not rhGH, significantly increased cortisol levels. Left ventricular ejection fraction (LVEF), mean blood pressure (MBP) and heart rate (HR) were unaffected by rhGH (62.4+/-2.1 vs 62.1+/-2.3%, 90.6+/-3.4 vs 92.0+/-2.5 mm Hg, 62.3+/-1.8 vs 66.7+/-2.7 bpm). HEX increased LVEF (70.7+/-3.0 vs 64.0+/-1.5%, p<0.03) without significant changes in MBP and HR (92.8+/-4.7 vs 92.4+/-3.2 mm Hg, 63.1+/-2.1 vs 67.0+/-2.9 bpm). LVEF significantly raised at 15 min, peaked at 30 min and lasted up to 60 min after HEX. These findings suggest that in man, the acute administration of Hexarelin exerts a short-lasting, positive inotropic effect. This effect seems GH-independent and might be mediated by specific GHS myocardial receptors.

Radionuclide angiocardiographic evaluation of the cardiovascular effects of recombinant human IGF-I in normal adults.

OBJECTIVE: IGF-I possesses specific myocardial receptors and is able to promote cardiac remodelling and even inotropic effects in both humans and other animals. In fact, reduced cardiac mass and performance are present in GH deficiency and these alterations are counteracted by recombinant human (rh) GH replacement, restoring IGF-I levels. Recently, the acute administration of 60 microg/kg rhIGF-I has also been reported to be able to improve cardiac performance evaluated by echocardiography or impedance cardiography in normal subjects. The aim of our study was to verify the effects of a subcutaneous low dose of rhIGF-I (20 microg/kg) on cardiac performance in humans. METHODS: In six healthy male adults (mean+/-S. e.m.: 35.7+/-4.3 years of age), the effects of rhIGF-I on left ventricular function evaluated by radionuclide angiocardiography and on circulating IGF-I, GH, insulin, glucose and catecholamines levels were studied. RESULTS: Administration of rhIGF-I increased circulating IGF-I (peak at +150 min vs baseline: 330.2+/- 9.6 vs 199. 7+/-8.7 microg/l, P<0.03) to levels which persisted similarly up to +180min. Neither GH nor catecholamine levels were modified by rhIGF-I administration, while insulin and glucose levels showed a slight but significant decrease. Basal left ventricular ejection fraction (61.8+/-2.0%) significantly increased at +180 min after rhIGF-I (65.3+/-2.7%, P<0.03). No change was recorded in mean blood pressure while a non-significant trend towards a reduction of heart rate was present by +120 min. CONCLUSIONS: These findings indicate that even subcutaneous administration of a low dose of rhIGF-I has acute inotropic effects as evaluated by radionuclide angiocardiography in healthy adults.

Effect of somatostatin infusion on the somatotrope responsiveness to growth hormone-releasing hormone in patients with anorexia nervosa.

BACKGROUND: According to the existence in anorexia nervosa (AN) of peripheral growth hormone (GH) resistance, low circulating insulinlike growth factor I (IGF-I) levels may be coupled with GH hypersecretion; however, there is also evidence for alterations in the neural control of GH secretion. In fact, reportedly GH secretion is partially refractory to the inhibitory effect of muscarinic cholinergic antagonists as well as to the stimulatory effect of muscarinic cholinergic agonists, which act via opposite modulation of hypothalamic somatostatin (SS) release. Thus, somatostatinergic activity could be impaired in AN. This could be due to an impaired hypothalamic SS release or, alternatively, an altered somatotroph sensitivity to SS. METHODS: We studied in 10 women with AN in acute phase (AN, age, mean +/- SEM: 18.7 +/- 0.8 years) the effect of exogenous SS1-14 (25 and 75 micrograms/hour i.v., infused from +15 to +75 min), at doses that had previously been shown capable of increasing circulating SS levels within the physiological range, on the GH response to GH-releasing hormone (GHRH) (1 microgram/kg i.v. at 0 min). The same study protocol was performed in 8 normal age-matched women (NW, 22.9 +/- 1.0 years). RESULTS: In AN patients, IGF-I levels were lower (p < .01) than those in NW, while basal GH levels were similar in both groups. The GHRH-induced GH rise in AN was higher (p < .01) than that in NW. In AN, the exaggerated GH response to GHRH was inhibited to the same extent by both SS doses (p < .05) and became similar to that after GHRH alone in NW. In NW both 25 and 75 micrograms/hour SS decreased the GHRH-induced GH response; however, the inhibitory effect of the lower dose did not attain statistical significance, whereas the higher dose did (p < .02). During SS infusion, the GHRH-induced GH response in NW was persistently lower (p < .02) than that in AN. The percent inhibitory effect of SS on the somatotroph responsiveness to GHRH was similar in both groups at each dose. CONCLUSIONS: Our present findings demonstrate that the sensitivity of somatotroph cells to exogenous SS given at physiological doses is preserved in patients with AN. It is noteworthy that, during the infusion of physiological SS doses, the GH response to GHRH in AN overlaps on that to GHRH alone under physiological conditions. Thus, in AN, the sensitivity of somatotroph cells to SS apparently being preserved, an impairment of somatostatinergic neurons cannot be ruled out.

Effects of recombinant human insulin-like growth factor I administration on growth hormone (GH) secretion, both spontaneous and stimulated by GH-releasing hormone or hexarelin, a peptidyl GH secretagogue, in humans.

The negative feedback exerted by insulin-like growth factor I (IGF-I) on GH secretion occurs at the pituitary, as well as the hypothalamic level, via stimulation of SS and/or inhibition of GHRH release. In fact, recombinant human IGF-I (rhIGF-I) administration inhibits basal GH secretion, at least in fasted humans, though its effect on the GH response to GHRH is still controversial. GH secretagogues (GHS) are peptidyl and nonpeptidyl molecules that act on specific receptors at the pituitary and/or the hypothalamic level. Contrary to GHRH, the GH-releasing activity of GHS is strong, reproducible, and even partially refractory to inhibitory influences such as exogenous somatostatin. We studied the effects of rhIGF-I administration (20 microg/kg s.c. at 0 min) on GH secretion, either spontaneous or stimulated by GHRH (2 microg/kg i.v. at +180 min) or Hexarelin (HEX, 2.0 microg/kg i.v at +180 min), a GHS, in eight normal young women (age, mean +/- SEM, 28.3 +/- 1.2 yr; body mass index, 20.1 +/- 0.5 kg/m2). rhIGF-I administration increased IGF-I levels (peak vs. baseline: 420.3 +/- 30.5 vs. 274.4 +/- 25.3 microg/L, P < 0.05) within the physiological range from +120 to +300 min. No variation in glucose or insulin levels was recorded. rhIGF-I did not reduce spontaneous GH secretion [areas under curves (AUC)(0-300 min) 140.6 +/- 66.3 vs. 114.6 +/- 32.1 microg/L x h], whereas it inhibited the GH response to both GHRH (AUC(180-300 min) 447.7 +/- 159.4 vs. 715.9 +/- 104.3 microg/L x h, P < 0.05) and HEX (620.3 +/- 110.4 vs. 1705.9 +/- 328.9 microg/L x h, P < 0.03). The percent inhibitory effect of rhIGF-I on the GH response to GHRH (41.7 +/- 12.8%) was lower than that on the response to HEX (57.7 +/- 11.0%). In fact, the GH response to GHRH alone was clearly lower than that to HEX alone (P < 0.05), whereas the GH responses to GHRH and HEXwere similar after rhIGF-I. Our findings show that the sc administration of low rhIGF-I doses inhibits the GH response to GHRH and, even more, that to HEX; whereas, at least in this experimental design in fed conditions, it does not modify the spontaneous GH secretion. Because GHS generally show partial refractoriness to inhibitory inputs, including exogenous somatostatin, the present results point toward a peculiar sensitivity of GHS to the negative feedback action of IGF-I.

GH response to GHRH combined with pyridostigmine or arginine in different conditions of low somatotrope secretion in adulthood: obesity and Cushing's syndrome in comparison with hypopituitarism.

BACKGROUND: Diagnosing GH deficiency in adults is difficult due to the age-related variations of GH/IGF-I axis and the influence of nutrition. Nowadays, GH replacement is allowed for patients with GH peak to provocative stimuli < 3 micrograms/L. Somatotrope insufficiency is present in hypopituitarism but also in obesity and hypercortisolism. However, to evaluate GH insufficiency in adults is difficult due to variations of GH and IGF-I levels as function of age and nutrition status. METHODS: We aimed to verify the GH response to GHRH (1 mg/kg i.v.) combined with pyridostigmine (PD, 120 mg p.o.) or arginine (ARG, 0.5 g/kg i.v.), in 26 hypopituitaric patients (GHD), in 11 obese women (OB), in 8 women with Cushing's syndrome (CS), and in 72 control subjects (NS). RESULTS: IGF-I levels in GHD were lower than those in OB (p < 0.01) and in CS (p < 0.01) which, in turn, were lower to those in NS (p < 0.02). In NS, the GH peak responses to GHRH + PD and GHRH + ARG were similar and the minimum normal GH peak was 16.5 mg/L. GHD had GH responses similar, lower than those in NS (p < 0.01) and always below the normal limit. However, only 12/20 and 8/14 had peaks < 3 micrograms/L; conventionally, below this limit severe GH deficiency is shown and rhGH replacement is allowed. In OB, the GH responses to GHRH + PD and GHRH + ARG were similar, lower (p < 0.01) and higher (p < 0.01) than those in NS and GHD, respectively. Six out of 11 OB had GH peaks below the normal limits but nobody < 3 micrograms/L. In CS, the GH response to GHRH + PD was lower than that to GHRH + ARG (p < 0.01); both these responses were lower than those in NS (p < 0.01) and even in OB (p < 0.01) but higher than those in GHD (p < 0.01). All and 7/8 CS had GH peaks lower than normal limits after PD + GHRH and ARG + GHRH, respectively while 6/8 showed GH peak < 3 micrograms/L after PD + GHRH but only 1 after ARG + GHRH. CONCLUSIONS: Present data demonstrate that the maximal somatotrope secretory capacity is reduced in OB and even more in CS. From a diagnostic point of view, PD + GHRH and ARG + GHRH tests distinguish OB from severe GHD. As hypercortisolism impairs the activity of cholinesterase inhibitors, only ARG + GHRH, but not PD + GHRH is a reliable test to explore the maximal somatotrope secretory capacity in CS. Notably, even with the ARG + GHRH test, in CS the maximal somatotrope secretory capacity is sometimes so reduced as to overlap with that of severe GHD.

IGF-I levels in prepubertal and pubertal children with Down syndrome.

BACKGROUND: Growth retardation is a main feature of Down syndrome but it is still unclear whether an alteration of the GH/IGF-I axis is present in this condition. Concerning IGF-I levels, they have been found reduced by some authors but normal by others. METHODS: On these bases, IGF-I levels have been assessed from prepubertal to late pubertal stages of gonadal maturation in a large group of children and adolescents with Down syndrome (DS, 68 M, 45 F, 12.5 +/- 0.6 yr; prepubertal n = 39, pubertal n = 74) with those in a group of normal children and adolescents (NS, 75 M, 87 F; 11.1 +/- 0.4 yr; prepubertal n = 94, pubertal n = 68). RESULTS: Within each group, IGF-I levels were gender-independent while showed age-related variations with positive association with pubertal stage--peaking up in pubertal stage IV--(DS: r = 0.6, NS: r = 0.4, both p < 0.0001) and testosterone (DS: r = 0.6, NS: r = 0.5, p < 0.001) or estradiol (DS: r = 0.6, NS: r = 0.5, p < 0.001) levels. Considering whole groups, mean IGF-I levels in DS were slightly but significantly lower than those in NS (257.9 +/- 12.5 vs 310.8 +/- 12.6 micrograms/l, p < 0.02). Analyzing individual IGF-I levels in DS with respect to normal ranges per pubertal stage, more than 85% of IGF-I levels resulted within the normal limits. These results demonstrate that IGF-I levels in DS patients are generally within the normal range--though a slight reduction of mean IGF-I levels is present--and follow normal age-related variations with clear cut increase at puberty and positive association with gonadal steroid levels. CONCLUSIONS: This evidence points toward the need to clarify the GH/IGF-I axis function and activity in DS patients.

GH response to GHRH combined with pyridostigmine or arginine in different conditions of low somatotrope secretion in adulthood: obesity and Cushing's syndrome in comparison with hypopituitarism.

BACKGROUND: Diagnosing GH deficiency in adults is difficult due to the age-related variations of GH/IGF-I axis and the influence of nutrition. Nowadays, GH replacement is allowed for patients with GH peak to provocative stimuli < 3 micrograms/L. Somatotrope insufficiency is present in hypopituitarism but also in obesity and hypercortisolism. However, to evaluate GH insufficiency in adults is difficult due to variations of GH and IGF-I levels as function of age and nutrition status. METHODS: We aimed to verify the GH response to GHRH (1 microgram/kg i.v.) combined with pyridostigmine (PD, 120 mg p.o.) or arginine (ARG, 0.5 g/kg i.v.), in 26 hypopituitaric patients (GHD), in 11 obese women (OB), in 8 women with Cushing's syndrome (CS), and in 72 control subjects (NS). RESULTS: IGF-l levels in GHD were lower than those in OB (p < 0.01) and in CS (p < 0.01) which, in turn, were lower to those in NS (p < 0.02). In NS, the GH peak responses to GHRH + PD and GHRH + ARG were similar and the minimum normal GH peak was 16.5 micrograms/L. GHD had GH responses similar, lower than those in NS (p < 0.01) and always below the normal limit. However, only 12/20 and 8/14 had peaks < 3 micrograms/L; conventionally, below this limit severe GH deficiency is shown and rhGH replacement is allowed. In OB, the GH responses to GHRH + PD and GHRH + ARG were similar, lower (p < 0.01) and higher (p < 0.01) than those in NS and GHD, respectively. Six out of 11 OB had GH peaks below the normal limits but nobody < 3 micrograms/L. In CS the GH response to GHRH + PD was lower than that to GHRH + ARG (p < 0.01); both these responses were lower than those in NS (p < 0.01) and even in OB (p < 0.01) but higher than those in GHD (p < 0.01). All and 7/8 CS had GH peaks lower than normal limits after PD + GHRH and ARG + GHRH, respectively while 6/8 showed GH peak < 3 micrograms/L after PD + GHRH but only 1 after ARG + GHRH. CONCLUSIONS: Present data demonstrate that the maximal somatotrope secretory capacity is reduced in OB and even more in CS. From a diagnostic point of view, PD + GHRH and ARG + GHRH tests distinguish OB from severe GHD. As hypercortisolism impairs the activity of cholinesterase inhibitors, only ARG + GHRH, but not PD + GHRH is a reliable test to explore the maximal somatotrope secretory capacity in CS. Notably, even with the ARG + GHRH test, in CS the maximal somatotrope secretory capacity is sometimes so reduced as to overlap with that of severe GHD.

Further evidence of cholinergic impairment of the neuroendocrine control of the GH secretion in Down's syndrome.

There are data indicating that cholinergic activity is precociously impaired in Down's syndrome (DS). On the other hand, acetylcholine as well as arginine (ARG) play a major stimulatory role in the neural control of growth hormone (GH) secretion in humans, likely acting via the inhibition of hypothalamic somatostatin release. The aim of the present study was to verify the effects of pyridostigmine (PD, 120 mg p.o.), a cholinesterase inhibitor, and ARG (0.5 g/kg i.v.) on the growth hormone-releasing hormone (GHRH) (1 microgram/kg i.v.)-induced GH rise in 15 adult patients with DS (M/F: 8/7; age 26.5 +/- 2.2 years; body mass index, BMI: 25.7 +/- 1.0 kg/m2) in which the potentiating effect of PD on GH secretion has been reported to be reduced. The results in DS were compared to those in 15 normal subjects (NS) (M/F: 8/7; age: 30.0 +/- 1.3 years; BMI: 21.4 +/- 0.4 kg/m2). Basal GH and insulin growth factor I (IGF-1) levels in DS (1.8 +/- 0.7 and 206.5 +/- 21.0 micrograms/l) were similar to those in NS (1.4 +/- 0.3 and 179.4 +/- 11.0 micrograms/l). The GH response to GHRH alone in DS (526.5 +/- 120.1 micrograms/l/h) was lower (p < 0.05) than that recorded in NS (895.4 +/- 153.7 micrograms/l/h). The GHRH-induced GH rise was potentiated by PD both in DS (1,138 +/- 184.2 micrograms/l/h; p < 0.02 vs. GHRH alone) and in NS (2,213.8 +/- 212.8 micrograms/l/h; p < 0.005 vs. GHRH alone); however, as the percent potentiating effect of PD was similar in both groups (215 and 247%, respectively) the GH response to GHRH + PD in DS was lower (p < 0.005) than that in NS. The GHRH-induced GH rise was also potentiated by ARG in both DS (2,243 +/- 362.4 micrograms/h; p < 0.001 vs. GHRH alone) and NS (2,764.3 +/- 325.7 micrograms/l/h; p < 0.005 vs. GHRH alone). As the percent potentiating effect of ARG in DS was more marked than in NS (425 vs. 308%, respectively), the GH response to GHRH + ARG became similar in both groups. No sex-related difference was found in the GH response to various stimuli both in DS and NS. In conclusion, these data demonstrate that the potentiating effect of PD but not that of ARG is impaired in adults with DS in whom a reduced somatotrope responsiveness to GHRH is present. These findings indicate that in DS the pituitary GH releasable pool is fully preserved while an impairment of the tuberoinfundibular cholinergic pathways could lead to somatostatinergic hyperactivity and low somatotrope responsiveness to GHRH.

Effects of beta-adrenergic agonists and antagonists on the growth hormone response to growth hormone-releasing hormone in anorexia nervosa.

BACKGROUND: In anorexia nervosa (AN), growth hormone (GH) hypersecretion and low insulin-like growth factor I (IGF-I) levels are present. It is unclear whether this is due to a peripheral GH resistance and a reduced IGF-I negative feedback on GH secretion or to a primary hypothalamic dysfunction. In AN, in contrast to normal subjects, cholinergic antagonists and agonists, whose action is somatostatin (SS)-mediated, have reduced and absent effects on the GH response to growth hormone-releasing hormone (GHRH). Since arginine, another substance acting via inhibition of SS, maintains its potentiating effect on GH secretion in AN, it has been hypothesized that somewhat specific alteration of the SS-mediated cholinergic influence may be present in this condition. To further clarify the neural control of AH secretion in AN, we evaluated the effects of beta-adrenergic agonists and antagonists, which are known to inhibit and increase, respectively, the GHRH-induced GH secretion in normal subjects. METHODS: We studied the effect of atenolol (ATE), a beta 1-adrenergic antagonist, and salbutamol (SALB), a beta 2-adrenergic agonist, on the GHRH-induced GH release in 10 patients with AN and in 10 normal age-matched women (NW). RESULTS: Basal GH levels were higher, whereas IGF-I were lower in AN than in NW. The GHRH-induced GH rise in AN was higher than that in NW. ATE significantly enhanced the GH response to GHRH in NW, but not in AN. The GH responses to GHRH after ATE pretreatment were similar in NW and in AN. The GH response to GHRH was inhibited by SALB in both NW and AN. The GH responses to GHRH after SALB pretreatment were similar in NW and AN. CONCLUSIONS: These data reveal an exaggerated somatotrope responsiveness to GHRH in AN that is not further increased by beta-adrenergic blockade, while is abolished by beta-adrenergic activation. This suggests that an impairment of beta-adrenergic influence on GH secretion is present in anorexia nervosa.

Maximal secretory capacity of somatotrope cells in obesity: comparison with GH deficiency.

OBJECTIVE: To evaluate the maximal secretory capacity of somatotrope cells in obesity and to compare it with that in hypopituitaric patients with GH deficiency. DESIGN: Stimulation with GHRH. (1 microgram/kg i.v.), combined with arginine (ARG, 0.5 g/kg i.v.), which strongly potentiates the GH response to the neurohormone, likely inhibiting hypothalamic somatostatin. The reproducibility of the GH response to GHRH + ARG was evaluated in a second session. SUBJECTS: Forty-five patients with simple obesity (OB 11 male and 34 female, age 40.5 +/- 1.8 y, BMI 38.8 +/- 1.1 kg/m2), 49 patients with hypopituitarism (GHD, 23 male and 26 female, 43.6 +/- 2.4 y, 24.7 +/- 0.7 kg/m2) and 44 normal young volunteers (NS, 25 male and 19 female, 33.8 +/- 1.0 y, 21.6 +/- 0.3 kg/m2) were studied. MEASUREMENTS: GH levels were assayed by IRMA method, basally at -60 and 0 min, and than every 15 min up to +120 min. Basal IGF-I levels were assayed by RIA method, after acid-ethanol extraction. RESULTS: IGF-I levels in OB were lower (P < 0.005) than those in NS but higher (P < 0.005) than those in GHD. Mean peak GH response to GHRH + ARG in OB was clearly lower than that in NS (P < 0.005) and higher (P < 0.005) than that in GHD. Sixty-percent OB and 100% GHD showed peak GH responses lower than the minimum normal limit in NS (16.5 micrograms/l) while 4% OB and only 53% GHD with GH responses lower than 3 micrograms/l, the limit under which GH replacement therapy of severe deficiency is allowed. Good intraindividual reproducibility of the GH response to GHRH + arginine test was present in all groups (OB: r = 0.78, P < 0.0001; GHD: r = 0.57, P < 0.003; NS: r = 0.74, P < 0.0001;. CONCLUSIONS: The maximal secretory capacity of somatotrope cells is clearly less than normal in the obese but still more than is seen in GHD subjects. However, in about 50% of obese patients, the pituitary GH releasable pool overlaps with that of hypopituitaric patients with GH deficiency. Thus, even when the maximal secretory capacity of somatotrope cells is evaluated by a potent and reproducible provocative tests such as GHRH + arginine, overweight has to be taken in a great account as the cause of severely impaired GH response in patients with suspected GH deficiency.

The inhibitory effect of glucose on growth hormone secretion is lost in obesity but not in hypertension.

In obesity there is a clear reduction of both spontaneous and stimulated GH secretion. Furthermore, in obese patients the somatotrope responsiveness to provocative stimulation is selectively refractory to the inhibitory effect of glucose load. It has been hypothesized that hyperinsulinism of obese patients could play a role in the pathogenesis of these alterations. Aim of the present study was to verify the GH response to GHRH and the ability of glucose load to inhibit it in patients with essential hypertension in whom hyperinsulinism and insulin resistance are frequently present. To this goal, 7 patients with essential hypertension (HP, age, mean +/- SE: 29.6 +/- 2.4 yr, 3 females and 4 males, BMI: 21.7 +/- 1.2 kg/m2), 7 obese (OB, 4 females and 3 males, 31.9 +/- 4.1 yr, 35.6 +/- 2.0 kg/m2) and 7 normal subjects (NS, 4 females and 3 males, 28.3 +/- 3.9 yr, 21.0 +/- 1.6 kg/m2) underwent the following tests: GHRH (1 microgram/kg i.v. at time 0) alone and preceded by oral glucose load (OGTT, 100 g po at -45 min). Basal insulin levels were similar in HP and OB (11.3 +/- 0.5 and 12.7 +/- 2.2 microU/ml, respectively); these, in turn, were higher (p < 0.005) than those in NS (6.8 +/- 0.8 microU/ml). Basal plasma glucose levels in HP were similar to those in OB and NS (80.3 +/- 3.6, 86.9 +/- 6.7 and 84.4 +/- 1.7 mg/dl, respectively). In HP and OB and NS basal GH (1.0 +/- 0.5, 1.0 +/- 0.6 and 0.3 +/- 0.1 micrograms/l, respectively) and IGF-I levels (132.6 +/- 14.8, 137.3 +/- 13.2 and 138.8 +/- 12.2 micrograms/l, respectively) were similar. In HP the GH response to GHRH (AUC: 1058.8 +/- 347.8 micrograms/l/min) was similar to that observed in NS (959.0 +/- 167.8 micrograms/l/min) and higher than that in OB (344.8 +/- 67.2 micrograms/l/min, p < 0.01). OGTT clearly blunted (p < 0.01) the GHRH-induced GH response in HP as well as in NS (401.8 +/- 104.4 and 521.6 +/- 76.6 (g/l/min, respectively) but not in OB (387.4 +/- 78.8 (g/l/min). The OGTT-induced insulin levels in HP did not differ from those of OB, both being higher (p < 0.05) than those recorded in NS. Glucose levels after OGTT were similar in the three groups. In conclusion, this study demonstrates that, like in normal subjects but differently from in obese patients the GH response to GHRH is normal in patients with essential hypertension and it is normally inhibited by oral glucose load even when these patients show high insulin levels. Thus, it is unlikely that the low somatotrope secretion and its refractoriness to inhibition by glucose load in obesity is due to hyperinsulinism.

Reproducibility of the growth hormone response to stimulation with growth hormone-releasing hormone plus arginine during lifespan.

The reliability and reproducibility of provocative stimuli of growth hormone (GH) secretion in the diagnosis of GH deficiency are still controversial both in childhood and in adulthood. The combined administration of GH-releasing hormone (GHRH) and arginine (ARG), which likely acts via inhibition of hypothalamic somatostatin release, is one of the most potent stimuli known so far and has been proposed recently as the best test to explore the maximal somatotrope capacity of somatotrope cells. However, it is well known that, usually, provocative stimuli of GH secretion suffer from poor reproducibility and that of the GHRH + ARG test has still to be verified. We aimed to verify the between- and within-subject variability of the GH response to the GHRH + ARG test in normal subjects during their lifespan as well as in hypopituitaric patients with GH deficiency (GHD). In 10 normal children (C: six male and four female, age 12.3 +/- 0.9 years, body mass index (BMI) = 16.6 +/- 0.7 kg/m2, pubertal stages I-III), 18 normal young adults (Y: ten male and eight female, age 31.1 +/- 1.3 years, BMI = 21.4 +/- 0.4 kg/m2), 12 normal elderly subjects (E: two male and ten female, age 74.4 +/- 1.8 years, BMI= 22.6 +/- 0.6 kg/m2) and 15 panhypopituitaric GH-deficient patients (GHD: nine male and six female, age 40.9 +/- 4.1 years, BMI= 22.7 +/- 1.0 kg/m2), we studied the inter- and intra-individual variability of the GH response to GHRH (1 microg/kg i.v.) + ARG (0.5 g/kg i.v.) in two different sessions at least 3 days apart. The GH responses to GHRH + ARG in C (1st vs 2nd session: 61.6 +/- 8.1 vs 66.5 +/- 9.4 microg/l), Y (70.4 +/- 10.1 vs 76.2 10.7 microg/l) and E (57.9 14.8 vs 52.1 +/- 8.0 microg/l) were similar and reproducible in all groups. The somatotrope responsiveness to GHRH + ARG also showed a limited within-subject variability (r = 0.71, 0.90 and 0.89 and p < 0.02, 0.0005 and 0.0005 for C, Y and E, respectively). Similarly in GHD, the GH response to the GHRH + ARG test showed a good inter- (1st vs 2nd session: 2.3 +/- 0.5 vs 2.2 +/- 0.6 microg/l) and intra-individual reproducibility (r = 0.70, p < 0.005). The GHRH + ARG-induced GH responses in GHD were markedly lower (p < 0.0005) than those in age-matched controls and no overlap was found between GH peak responses in GHD and normal subjects. In normal subjects, the GH response to GHRH + ARG is very marked, independent of age and shows limited inter- and intra-individual variability. The GH response to the GHRH + ARG test is strikingly reduced in panhypopituitaric patients with GHD, in whom the low somatotrope responsiveness is reproducible. Thus, these findings strengthen the hypothesis that GHRH + ARG should be considered the most reliable test to evaluate the maximal secretory capacity of somatotrope cells and to distinguish normal subjects from GHD patients in adulthood.

Acute administration of recombinant human growth hormone inhibits the somatotrope responsiveness to growth hormone-releasing hormone in childhood.

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 i.v. administration of different recombinant human GH doses (group 1, N = 5, 0.06 U/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 microgram/kg i.v. 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 i.v. 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 micrograms/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 micrograms/l, p < 0.05; group 2, 9.5 +/- 2.8 vs 26.9 +/- 8.5 micrograms/l, p < 0.05; group 3, 9.1 +/- 2.7 vs 34.8 +/- 7.2 micrograms/l, p < 0.02). The GH response to arginine + GHRH (56.9 +/- 13.3 micrograms/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 micrograms/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.

The enhancing effect of pyridostigmine on the GH response to GHRH undergoes an accelerated age-related reduction in Down syndrome.

Cholinergic agonists are known to potentiate GHRH-induced GH secretion, probably acting via inhibition of hypothalamic somatostatin release. Their effect is reduced in aging and in patients with Alzheimer's disease. This may be the consequence of age-related cholinergic impairment, which, in turn, could cause somatostatinergic hyperactivity leading to GH hyposecretion. As in Down syndrome (DS) neural alterations have been reported similar to those in aging, including cholinergic impairment, we verified the GH response to GHRH (1 microgram/kg i.v. at 0 min) alone or combined with pyridostigmine (PD), a cholinesterase inhibitor (60 and 120 mg, respectively, in children and adults, orally at -60 min) in 15 DS children (13.5 +/- 0.6 years) and in 11 DS young adults (24.0 +/- 1.2 years). Fifteen normal children (11.9 +/- 0.5 years), 15 normal adults (27.3 +/- 0.9 years) and 16 normal elderly (76.3 +/- 1.5 years) were studied as controls. IGF-I levels showed an age-related reduction both in DS (children vs. adults, mean +/- SEM:354.8 +/- 44.9 vs. 204.4 +/- 29.4 micrograms/l, p < 0.02) and in controls (normal children vs. normal adults vs. normal elderly:281.4 +/- 36.3 vs. 175.4 +/- 11.2 vs. 72.5 +/- 6.6 micrograms/l, p < 0.001). The GH response to GHRH in DS children was higher than in DS adults (areas under curve: 1,197.6 +/- 241.5 vs. 434.4 +/- 83.3 micrograms/l/h, p < 0.01). On the other hand, in normal subjects the GHRH-induced GH rise was similar in children and adults (1,056.2 +/- 128.4 vs. 800.8 +/- 124.5 micrograms/l/h) and both were higher than that in elderly subjects (296.0 +/- 61.0 micrograms/l/h, p < 0.001). PD enhanced the GH response to GHRH both in DS and in normal subjects (p < 0.005). The GH response to PD+GHRH was lower in DS adults than in DS children (1,068.1 +/- 145.7 vs. 1,897.4 +/- 198.8 micrograms/l/h, p < 0.001) as well as in normal elderly subjects with respect to that in normal children and normal adults (832.3 +/- 144.7 vs. 2,172.1 +/- 156.1 and 2,347.6 +/- 322.4 micrograms/l/h, respectively, p < 0.001). The GH response to GHRH alone or combined with PD in DS adults was lower (p < 0.01) than that in normal adults and similar to that in normal elderly subjects. In conclusion, the present data demonstrate that the stimulated GH secretion in DS undergoes an accelerated age-related reduction. They also suggest the existence of a precocious impairment of central cholinergic activity in DS, which, in turn, could cause somatostatinergic hyperactivity and reduced GH secretion.