Identification of a pituitary growth hormone-releasing peptide (GHRP) receptor subtype by photoaffinity labeling.

Hexarelin, an analogue of GHRP-6, in which D-Tryptophan has been replaced by its 2-methyl derivative, is known to release growth hormone (GH) in vivo and in vitro by direct action on receptors present in anterior pituitary cells. Measurement of second messengers (c-AMP, Ca++, IP3) upon somatotrophs stimulation, suggests the existence of more than one GHRP receptor subtype. In order to document such an hypothesis, we have used a new photoactivatable derivative of Hexarelin, Tyr-Bpa-Ala-Hexarelin. This derivative was shown to be fully active in the release of GH in vivo with neonate rats. Using this photoactivatable ligand, we have specifically labeled a protein with an apparent Mr of 57,000 in human, bovine and porcine anterior pituitary membranes. Hexarelin and the spiroindoline sulfonamide MK-0677 displaced the Mr-57,000 photolabeled band with an apparent ED50 of 6x10(-7) M and 2x10(-5) M respectively. Taking into account the high efficiency (>60%) of covalent incorporation of the Bpa residue, this photoactivatable Hexarelin derivative has allowed the identification of a pituitary GHRP receptor subtype, which is apparently distinct from the recently cloned GH secretagogue receptor.

Intranasal administration of neostigmine potentiates both intravenous and intranasal growth hormone (GH)-releasing hormone-induced GH release in short children.

Administration of cholinergic agonists increases both basal and GH-releasing hormone (GHRH)-induced GH secretion, probably acting via inhibition of endogenous somatostatin release. The aim of our study was to verify in two groups of children with idiopathic short stature the effect of intranasal administration of neostigmine (inNS; 3 mg), a cholinesterase inhibitor, on basal GH levels as well as on the somatotroph response to GHRH when the peptide was administered either iv (ivGHRH; 1 microgram/kg) or intranasally (inGHRH; 10 micrograms/kg). In group A (n = 6; age, 10.6-16.0 yr) inNS induced a significant GH increase [inNS vs. saline, area under the curve (AUC; mean +/- SEM), 263.7 +/- 60.2 vs. 73.8 +/- 3.1 micrograms/L.h; P less than 0.03] and potentiated the somatotroph response to ivGHRH (inNS with ivGHRH vs. ivGHRH, 1316 +/- 183.0 vs. 644.9 +/- 154.5 micrograms/L.h; P less than 0.03). In group B (n = 6; age, 11.5-15.9 yr) ivGHRH induced a GH rise clearly higher than that induced by inGHRH (604.2 +/- 154.3 vs. 137.1 +/- 28.2 micrograms/L.h; P less than 0.03). Administration of inNS induced a GH rise similar to that occurring after inGHRH (AUC, 239.2 +/- 69.5 micrograms/L.h) and markedly increased the inGHRH-induced GH response (482.4 +/- 103.6 micrograms/L.h; P less than 0.05 and 0.03 vs. inNS and inGHRH, respectively), so that it overlapped with that induced by ivGHRH alone. In conclusion, cholinergic agonists such as neostigmine are able to increase both basal and GHRH-induced GH secretion in short children even when given intranasally. Combined intranasal administration of neostigmine and GHRH (10 micrograms/kg) is able to induce a GH rise similar to that induced by ivGHRH alone (1 microgram/kg), suggesting the potential usefulness of this combination cocktail and route of administration for the treatment of short stature.

Long-lasting prolactin-lowering effect of cabergoline, a new dopamine agonist, in hyperprolactinemic patients.

The new long-acting ergoline derivative cabergoline was given orally in a single dose of 300 micrograms to 15 hyperprolactinemic patients (including 4 acromegalic patients, 2 of whom were dopamine responsive). Serum PRL and GH levels were determined before and 3, 4, and 6 h and 1, 2, 3, 4, 5, 6, and 7 days after treatment. A control test with a single oral dose of 2.5 mg bromocriptine was also performed; serum PRL and GH levels were measured at the same time intervals for 2 days. Cabergoline induced a marked fall in serum PRL which began within 3 h and continued for 7 days. The maximal decrease ranged between -49.2% and -55.2% and occurred after 2-5 days. This maximal effect was only slightly less than that 6 h after bromocriptine treatment (-63.8%). After cabergoline treatment, serum GH levels did not change significantly in either nonacromegalic or acromegalic patients, whereas the two dopamine-responsive acromegalic patients had a marked GH fall after bromocriptine. A moderate blood pressure decrease, more evident in the standing position, occurred after both cabergoline and bromocriptine treatments. The only symptomatic side-effect was orthostatic hypotension after cabergoline in an elderly woman. These data indicate that cabergoline has potent and prolonged dopaminergic activity and may prove suitable for once weekly treatment of hyperprolactinemic patients.

Somatotropic function in short stature: evaluation by integrated auxological and hormonal indices in 214 children. The Italian Collaborative Group of Neuroendocrinology.

GH secretion was evaluated in 214 children and adolescents (age, 5-16 yr; 160 males and 54 females) with short stature (height, < or = 5th percentile) by assessing mean spontaneous overnight GH concentration (normal values, > or = 3 and 3.9 micrograms/L for prepubertal and pubertal subjects, respectively) and responsiveness to stimulation with GH-releasing hormone combined with pyridostigmine (normal peak values, > or = 20 micrograms/L). Plasma insulin-like growth factor-I (IGF-I) was also measured. According to their GH secretory status, children were grouped as follows: group I, 154 subjects with normal spontaneous and stimulated GH (43 slow-growing and 111 normally growing); group II, 39 subjects with low spontaneous, but normal stimulated, GH (27 slow-growing and 12 normally growing); group III, 18 slow-growing subjects with low spontaneous and stimulated GH; and group IV, 3 subjects with normal spontaneous, but low stimulated, GH. The following conclusions were drawn. 1) Forty-five slow-growing subjects (21% of the total sample) had GH deficiency; 27 (12.6%) belonged to group II (with a preserved GH pituitary reserve, denoting a hypothalamic dysfunction) and 18 (8.4%) to group III (with a reduced GH pituitary reserve). 2) Forty-three slow-growing children in group I had normal GH secretion but low mean IGF-I, which may indicate nutritional problems or a biologically hypoactive GH molecule. 3) The remaining 111 subjects in group I (52%), with normal growth rate, but low mean parental height, were considered as having familial and/or constitutional short stature. GH responses after pyridostigmine plus GH-releasing hormone were normal in all children with a normal growth rate. These findings show that besides clinical evaluation, the assessment of spontaneous GH secretion, GH pituitary reserve, and IGF-I concentration allows proper pathophysiological characterization of short stature. By this approach, the frequency of GH deficiency in our sample was higher than commonly thought.

Effects of ibopamine on serum prolactin and growth hormone levels in hyperprolactinemic and acromegalic subjects.

The effects of oral doses (100, 200, and 400 mg) of a dopamine derivative, ibopamine, on serum prolactin (PRL) and growth hormone (GH) levels were evaluated in hyperprolactinemic patients, some of whom also were acromegalic. There was dose-related lowering of PRL levels. The highest dose was as effective as 500 mg L-dopa, although the duration of action was shorter, with a decrease to below 50% of basal PRL values in all patients. Serum GH did not rise in nonacromegalic subjects, but it fell after 400 mg ibopamine in the L-dopa-sensitive acromegalic patients. These data suggest, but do not prove, that ibopamine is able to directly stimulate pituitary dopamine receptors.

Specific receptors for synthetic GH secretagogues in the human brain and pituitary gland.

In vitro studies have been performed to demonstrate and characterize specific binding sites for synthetic GH secretagogues (sGHS) on membranes from pituitary gland and different human brain regions. A binding assay for sGHS was established using a peptidyl sGHS (Tyr-Ala-hexarelin) which had been radioiodinated to high specific activity at the Tyr residue. Specific binding sites for 125I-labelled Tyr-Ala-hexarelin were detected mainly in membranes isolated from pituitary gland and hypothalamus, but they were also present in other brain areas such as choroid plexus, cerebral cortex, hippocampus and medulla oblongata with no sex-related differences. In contrast, negligible binding was found in the thalamus, striatum, substantia nigra, cerebellum and corpus callosum. The binding of 125I-labelled Tyr-Ala-hexarelin to membrane-binding sites is a saturable and reversible process, depending on incubation time and pH of the buffer. Scatchard analysis of the binding revealed a finite number of binding sites in the hypothalamus and pituitary gland with a dissociation constant (Kd) of (1.5 +/- 0.3) x 10(-9) and (2.1 +/- 0.4) x 10(-9) mol/l respectively. Receptor activity is sensitive to trypsin and phospholipase C digestion, suggesting that protein and phospholipids are essential for the binding of 125I-labelled Tyr-Ala-hexarelin. The binding of 125I-labelled Tyr-Ala-hexarelin to pituitary and hypothalamic membranes was displaced in a dose-dependent manner by different unlabelled synthetic peptidyl (Tyr-Ala-hexarelin, GHRP2, hexarelin, GHRP6) and non-peptidyl (MK 0677) sGHS. An inhibition of the specific binding was also observed when binding was performed in the presence of [D-Arg1-D-Phe5-D-Trp7,9-Leu11]-substance P, a substance P antagonist that has been found to inhibit GH release in response to sGHS. In contrast, no competition was observed in the presence of other neuropeptides (GHRH, somatostatin, galanin or Met-enkephalin) which have a known influence on GH release. In conclusion, the present data demonstrate that sGHS have specific receptors in human brain and pituitary gland and reinforce the hypothesis that these compounds could be the synthetic counterpart of an endogenous GH secretagogue involved in the neuroendocrine control of GH secretion and possibly in other central activities.

Growth hormone-releasing effect of oral growth hormone-releasing peptide 6 (GHRP-6) administration in children with short stature.

Growth hormone-releasing peptide 6 (GHRP-6) is a synthetic hexapeptide with a potent GH-releasing activity after intravenous, subcutaneous, intranasal and oral administration in man. Previous data showed its activity also in some patients with GH deficiency. The aim of our study was to verify the GH-releasing activity of oral GHRP-6 administration on GH secretion in children with normal short stature. The effect of oral GHRP-6 (300 micrograms/kg) was compared with that of the maximally effective dose of intravenous GH-releasing hormone (GHRH-29, 1 microgram/kg). As the GHRH-induced GH rise in children is potentiated by arginine (ARG), even when administered by oral route at low dose (4 g), we studied also the interaction of oral GHRP-6 and ARG administration. We studied 13 children (nine boys and four girls aged 6.2-10.5 years, pubertal stage I) with normal short stature (height less than -2 SD score; height velocity more than -2 SD score; normal bone age; insulin-like growth factor I > 70 micrograms/l). In a first group of children (N = 7), oral GHRP-6 administration induced a GH response (mean +/- SEM; peak at 60 min vs baseline: 18.8 +/- 3.0 vs 1.1 +/- 0.3 micrograms/l, p < 0.0006; area under curve: 1527.3 +/- 263.9 micrograms l-1 h-1) which was similar to that elicited by GHRH (peak at 45 min vs baseline: 20.8 +/- 4.5 vs 2.2 +/- 0.9 micrograms/l, p < 0.007; area under curve: 1429.4 +/- 248.2 micrograms l-1 h-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term administration of intranasal or oral Hexarelin, a synthetic hexapeptide, does not desensitize the growth hormone responsiveness in human aging.

The function of the growth hormone-insulin-like growth factor I (GH-IGF-I) axis is reduced in aging, although the secretory capacity of somatotrope cells is preserved. Previous studies have suggested that continuous administration of GH-releasing peptides (GHRPs) results in homologous desensitization to the GH-releasing effect of the peptides. In the present study we have studied whether healthy elderly subjects would remain responsive to short-term, intermittent treatment with Hexarelin (HEX), a GHRP, and whether this treatment would result in an increase in serum IGF-I. In study I, the effect of an 8-day treatment with intranasal administration of 1.25 mg (about 18 micrograms/kg) t.i.d. HEX on the acute GH response to the hexapeptide and on serum IGF-I, IGF binding protein 3 (IGFBP-3), prolactin and cortisol levels was studied in seven elderly subjects (four males and three females, aged 67-80 years). In study II, the same parameters were studied before and after a 15-day treatment with oral administration of 20 mg (about 300 micrograms/kg) t.i.d. HEX in seven elderly women (aged 63-80 years). The GH response to the intranasal HEX administration was not significantly higher than that induced by 1 microgram/kg iv GHRH (229.4 +/- 35.9 vs 145.8 +/- 26.9 micrograms.l-1.h-1) and was maintained with a trend towards increase after an 8-day treatment with the peptide (342.5 +/- 199.3 micrograms.l-1.h-1). On the other hand, HEX treatment did not significantly modify IGF-I (138.7 +/- 11.1 vs 122.4 +/- 14.1 micrograms/l) but increased IGFBP-3 levels (2.4 +/- 0.2 vs 1.6 +/- 0.2 mg/l, p < 0.02). The GH response to the oral HEX administration was also not significantly higher than that to iv GHRH (257.6 +/- 72.0 vs 179.0 +/- 42.8 micrograms.l-1.h-1) and did not change after a 15-day treatment with the peptide (237.8 +/- 42.8 micrograms.l-1.h-1). Both IGF-I and IGFBP-3 levels were slightly but significantly increased by oral HEX treatment (156.0 +/- 10.7 vs 141.6 +/- 13.6 micrograms/l, p < 0.03, 3.4 +/- 0.2 vs 3.1 +/- 0.2 mg/l, p < 0.03, respectively). Neither intranasal nor oral HEX treatment modified PRL or cortisol levels and did not induce any side effect. In conclusion, these results indicate that chronic but intermittent treatment with HEX, administered either by intranasal or oral route, does not desensitize the GH response to the peptide. Moreover, after HEX treatment a trend towards increase was shown for IGF-I and IGFBP-3 levels. Thus, our findings strengthen the hypothesis that prolonged treatment with HEX may restore the reduced GH release in aging.

Growth hormone-releasing activity of growth hormone-releasing peptide-6 is maintained after short-term oral pretreatment with the hexapeptide in normal aging.

The reduced activity of the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis in aging may contribute to changes in body composition. As this GH insufficiency is due to hypothalamic pathogenesis, the availability of GH-releasing peptides (GHRPs), such as GHRP-6 (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) which is active even after oral administration, might be useful to restore it. The aim of our study was to verify the effectiveness of oral administration of GHRP-6 in normal elderly subjects and to investigate whether its GH-releasing activity is maintained or vanishes after short-term oral treatment. Seven normal elderly women (aged 65-82 years) were studied. The effect of oral administration of 300 micrograms/kg GHRP-6 on GH secretion was investigated before and after 4 days of treatment with the hexapeptide given twice daily. The GH response to the maximal effective dose of GHRH (1 microgram/kg i.v.) also was studied. Before treatment, oral administration of 300 micrograms/kg GHRP-6 elicited a clear GH rise (peak 10.7 +/- 3.3 micrograms/l; AUC 353.1 +/- 90.6 micrograms.l-1.h-1), which was significantly higher (p < 0.01) than that induced by intravenous GHRH (peak 5.1 +/- 1.5 micrograms/l; AUC 106.5 +/- 43.9 micrograms.l-1.h-1). After 4 days of treatment with GHRP-6, the GH response to the hexapeptide was maintained, with a trend towards an increase (peak 16.8 +/- 2.9 micrograms/l; AUC 499.8 +/- 107.2 micrograms.l-1.h-1). The IGF-I levels were not increased significantly after treatment (77.1 +/- 8.4 vs 84.1 +/- 12.2 micrograms/l).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Mechanisms underlying the negative growth hormone (GH) autofeedback on the GH-releasing effect of hexarelin in man.

The growth hormone (GH) response to GH-releasing hormone (GHRH) is strongly inhibited by previous administration of recombinant human GH (rhGH), likely as a consequence of a somatostatin-mediated GH negative autofeedback. Hexarelin (HEX), a synthetic hexapeptide belonging to the GH-releasing peptide (GHRP) family, possesses a GH-releasing activity greater than that of GHRH both in animals and in man. The mechanism of action of GHRPs is yet to be completely clarified, although concomitant actions at the pituitary and hypothalamic level have been hypothesized. To further clarify the mechanisms of action underlying the GH-releasing activity of HEX, in six normal young volunteers we studied the effects of rhGH (2 U intravenously [IV]) on the GH response either to GHRH (2 microg/kg IV) or to HEX (2 microg/kg IV) alone or combined with GHRH and/or pyridostigmine ([PD], 120 mg orally). The GH-releasing effect of HEX was higher than that of GHRH (area under the curve [AUC], 2,200.8 +/- 256.9 v 792.2 +/- 117.6 microg/L/h, P < .001), whereas combined administration of the two substances induced a true synergistic effect, with GH release after HEX plus GHRH (4,259.2 +/- 308.0 microg/L/h) being higher (P < .02) than the arithmetic sum of the GH increases induced by each compound separately administered. After rhGH administration, the GH-releasing effect of HEX was blunted (1,468.9 +/- 193.7 microg/L/h, P < .04; inhibition of 32.1%), whereas that of GHRH was nearly abolished (102.0 +/- 7.8 microg/L/h, P < .02; inhibition of 86.1%). The GH response to combined administration of HEX and GHRH was also blunted by the previous rhGH bolus (3,070.6 +/- 481.8 microg/L/h, P < .02; inhibition of 26.7%). PD did not modify the GH-releasing effect of HEX either alone (2,456.8 +/- 317.5 microg/L/h) or combined with GHRH (4,009.1 +/- 360.8 microg/L/h). rhGH was again able to blunt the GH response to HEX combined with PD (1,619.3 +/- 237.9 microg/L/h, P < .02), but failed to modify the GH response to HEX combined with GHRH and PD (4,548.4 +/- 698.0 microg/L/h). In conclusion, these results demonstrate that rhGH administration only blunts the GH-releasing activity of HEX, but abolishes that of GHRH. The blunting effect of rhGH on the GH response to HEX is probably mediated by a concomitant reduction in the activity of GHRH-secreting neurons and an increase of somatostatinergic tone.

Effects of GHRP-2 and hexarelin, two synthetic GH-releasing peptides, on GH, prolactin, ACTH and cortisol levels in man. Comparison with the effects of GHRH, TRH and hCRH.

GHRP-2 (D-Ala-D-beta Nal-Trp-D-Phe-Lys-NH2) and Hexarelin (HEX) (His-D-2-methylTrp-Ala-Trp-DPhe-Lys-NH2) are synthetic, non-natural super-analogs of GHRP-6 endowed with potent stimulatory effect on GH secretion and slight stimulatory effect on PRL, ACTH and cortisol levels. Their GH-releasing activity ahs never been compared each other and their effects on PRL, ACTH and cortisol have never been compared with that of other stimuli. To clarify these points, in 6 normal young adults (22-27 yr) we studied the GH, PRL, ACTH and cortisol responses to 1 and 2 micrograms/kg i.v. GHRP-2 and HEX comparing them with that after 1 micrograms/kg i.v. GHRH and 400 micrograms i.v. TRH + 2 micrograms/kg i.v. hCRH. The Gh responses to 2 micrograms/kg i.v. GHRP-2 or HEX, compared with those to 1 microgram/kg GHRH, were also studied in 6 normal elderly subjects (66-73 yr). In young adults 1 microgram/kg i.v. GHRP-2 and HEX induced a similar, strong GH response, which was higher (p < 0.05) than that to GHRH. The administration of 2.0 micrograms/kg i.v. GHRP-2 and HEX again elicited a similar GH response, which was higher (p < 0.05) than that after the 1.0 microgram/kg dose. In elderly subjects, the GH those in young subjects. In young adults, the PRL responses to all doses of GHRP-2 or HEX were similar and lower (p < 0.01) responses were similar to those to hCRH. In conclusion, our results demonstrate that, in man, GHRP-2 and HEX have similar, 2 and HEX is not fully specific, as they induce similar increases in PRL, ACTH and cortisol levels. The PRL-releasing activity of GHRPs is lower than that of TRH while their ACTH/cortisol-releasing activity is similar to that of hCRH.

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.

Serum free thyroid hormones in T3-toxicosis: a study of 35 patients.

Few data are available on serum free thyroid hormone concentration in patients with T3-toxicosis. In this study total and free T4 and T3 and TBG were evaluated in 35 subjects with T3-toxicosis, including 12 with untreated Graves' disease, 5 Graves' patients on methimazole treatment, 13 with autonomous adenoma, 3 with multinodular goiter, and 2 with subacute thyroiditis. T4, T3, free T4 (FT4), free T3 (FT3) as well as calculated T4/TBG and T3/TBG ratios were significantly higher in patients than in 37 healthy controls. Serum FT4 levels above the normal range were found in 19 subjects with T3-toxicosis (9 with untreated and one with methimazole-treated Graves' disease, 6 with autonomous adenoma, 1 with multinodular goiter and 2 with subacute thyroiditis). These data, together with the few previous reports, indicate that high FT4 levels are present in about half of the patients with so called T3-toxicosis, and that this occurs more frequently in diffuse than nodular goiter. It is suggested that the term T3-toxicosis be used only for those subjects with normal total and free T4.

Effect of dihydroergokryptine administration on serum prolactin and growth hormone levels in normal, hyperprolactinaemic and acromegalic subjects: evidence of potent and long-lasting pituitary dopamine receptor stimulation.

The endocrine effects of a relatively potent dopaminergic agent, dihydroergokryptine, have been studied in normal subjects, and in hyperprolactinaemic and acromegalic patients. A single 6 mg oral dose of the drug caused a marked, long lasting fall in prolactin (PRL) plasma levels in healthy subjects, in hyperprolactinaemic patients and in normoprolactinaemic acromegalics. Growth hormone (GH) levels decreased in 1-DOPA - responder, acromegalic patients, but dihydroergokryptine did not affect GH levels in normal volunteers or in 1-DOPA non-responder, acromegalic patients. The PRL- and GH- lowering activity of 6 mg dihydroergokryptine was significantly greater than that of 6 mg dihydroergocristine, and was similar to that of an oral dose of 500 mg 1-DOPA.

Hepatic extraction of hexarelin, a new peptidic GH secretagogue, in the isolated perfused rat liver.

PURPOSE: To assess the hepatic extraction of hexarelin (HEX), a novel peptidyl GH secretagogue, in the isolated perfused rat model and document the in vitro binding of HEX to plasma proteins using plasma from rats, dogs, pigs, and humans. METHODS: Rat liver was perfused in situ using a recirculating system. The recirculating perfusate consisted of a Krebs Henseleit buffer containing 20% (v/v) prewashed bovine red blood cells, 1% albumin, and lg/L dextrose. Three HEX concentrations of 5, 50, and 500 ng/ml were examined. In vitro plasma binding was determined by the ultrafiltration method. RESULTS: The disappearance rate constant (K), half-life (t1/2), clearance (Cl), and hepatic extraction ratio (E) were: K = 0.013-0.014 min-1, t1/2 = 45-55 min, Cl = 0.345-0.401 ml/min/g liver, and E = 19-21% for the different concentrations of HEX. A linear increase in AUC (270-24334 min pmol/ml) was observed with increasing concentrations. Binding of HEX to plasma proteins of rats, dogs, pigs, and humans was 68.7 +/- 0.8%, 78.7 +/- 0.6%, 67.3 +/- 0.7%, and 65.2 +/- 0.6% respectively. Plasma binding was concentration-independent in the range between 0.003-3 microM for the four species examined. CONCLUSIONS: These results show that 1) the hepatic extraction of HEX is low, 2) the hepatic clearance is concentration independent up to 500 ng HEX/ml of perfusate, and 3) the plasma protein binding of HEX is significant over the dose range studied. HEX exhibits a low hepatic extraction ratio, allowing us to predict that its hepatic clearance may be limited upon HEX protein binding.

Long-lasting lowering of serum growth hormone and prolactin levels by single and repetitive cabergoline administration in dopamine-responsive acromegalic patients.

Cabergoline, the new long-acting dopaminergic ergoline derivative, was given orally in single doses of 0.3 and 0.6 mg to eight dopamine-responsive acromegalic patients. Serum GH and PRL levels were determined before treatment, 3, 4, and 6 h and 1, 3, 5, 7 and 14 days after treatment. A control test with a single oral dose of 2.5 mg of bromocriptine was also performed. Cabergoline induced a marked fall in serum PRL level, starting within 3 h and continuing for 7 days after administering 0.3 mg, and for 14 days after 0.6 mg. The mean maximal decrease was 49% after 0.3 mg and 63% after 0.6 mg and occurred after 24 h in both cases. The latter was of similar magnitude to that induced by bromocriptine (67% at 4 h). Serum GH levels did not change after 0.3 mg of cabergoline, but decreased significantly from 3 h to 3 days after 0.6 mg of the compound with a mean maximal decrease of 42% after 24 h, and from 3 to 6 h after giving bromocriptine (mean maximal decrease 63% at 4 h). Once a week repeated administration of 0.3-0.6 mg of cabergoline was carried out in six patients, five of whom had completed the acute study; a normalization of serum GH and insulin-like growth factor I (IGF-I) levels occurred in three patients, one of whom had very high pretreatment values. In three poorly or nonresponsive patients, a better response, as assessed by both GH and IGF-I levels, was induced by increasing the dose up to 0.6 mg twice or 0.4 mg three times a week; in one case this was associated with marked tumour shrinkage. Sustained normalization of PRL levels was achieved in all cases. These data indicate that a single dose of 0.6 mg of cabergoline inhibits GH as well as PRL secretion in dopamine-responsive acromegalic patients and suggests that doses of 0.3-0.6 mg once to three times a week may prove suitable for treatment of this condition.

Serum free thyroid hormones in different degrees of hypothyroidism and in euthyroid autoimmune thyroiditis.

Serum total and free T4 and T3, thyroxine-binding globulin (TBG) and TSH, basal and 20, 30 and 60 min after TRH (200 micrograms, iv), were evaluated in 125 hypothyroid patients (38 with severe, 23 with mild, and 64 with subclinical hypothyroidism), in 35 euthyroid subjects with autoimmune thyroiditis, and in 51 healthy controls. T4/TBG and T3/TBG ratios were also calculated. A significant decrease in all indices of thyroid function except for T3 occurred simultaneously with a significant increase in basal and TRH-stimulated TSH levels from healthy subjects to subclinical hypothyroids, from subclinical to mild and from mild to severe hypothyroids; euthyroid patients with autoimmune thyroiditis did not differ from healthy subjects. All severe hypothyroid patients had low T4 as well as free T4 (FT4), free T3 (FT3), T4/TBG and T3/TBG ratios, but among mild and subclinical hypothyroids direct determination of FT4 and FT3 proved to be a better index of thyroid function than determination of T4 and T3 even after correction for TBG levels. FT4 was the most commonly abnormal index (19 of 23 subjects with mild and 14 of 64 with subclinical disease). Regression analysis showed that FT4, T4/TBG ratio, T4, and FT3 had a significant inverse correlation with TSH in hypothyroid patients. Discriminant analysis showed that among the thyroid parameters, FT4 is the variable which discriminates best between control subjects and the 3 groups of hypothyroid patients. These data extend previous reports and in a large series of patients confirm the biological meaning and the clinical value of direct measurement of serum free thyroid hormones in hypothyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

Repetitive GHRH administration fails to increase the response to GHRH in obese subjects. Evidence for a somatotrope defect in obesity?

Spontaneous GH secretion as well as GH response to several stimuli including GHRH have been shown to be reduced in obesity. To clarify the pathogenesis underlying these alterations, in six obese patients (3 males and 3 females, age 20-44 yrs, BMI = 42.1 +/- 2.2) on unrestricted diet we studied the effect of 8 day GHRH pretreatment (1 micrograms/kg iv each day) on the acute somatotropic response to the neurohormone administered both alone and combined with arginine (ARG, 0.5 g/kg iv infused from 0 to 30 min) which likely inhibits the release of hypothalamic somatostatin. Before treatment the GH response to GHRH (AUC: 231.9 +/- 106.4 micrograms/l/h) was potentiated (p < 0.001) by ARG (932.6 +/- 166.2 micrograms/l/h). However, the GH responses to the neurohormone both alone and combined with ARG were lower (p < 0.02 and 0.002, respectively) than in normals (712.4 +/- 111.6 and 2608.3 +/- 453.2 micrograms/l/h, respectively). After repetitive GHRH administration, in obese subjects baseline GH and IGF-I levels were unchanged. Also the GH responses to GHRH both alone (217.3 +/- 68.1 micrograms/l/h) and combined with ARG (756.3 +/- 202.9 micrograms/l/h) were not modified. In conclusion, our data demonstrate the failure of GHRH pretreatment to improve the somatotrope hyporesponsiveness to GHRH both alone and combined with ARG suggesting the existence of a somatotropic defect in obesity.

Effect of the potentiation of cholinergic activity on the variability in individual GH response to GH-releasing hormone.

In man the GH response to GHRH is highly variable and some normal subjects may be completely unresponsive to the neuropeptide. On the other hand, the potentiation of cholinergic activity by pyridostigmine (PD), a cholinesterase inhibitor, increases the GH response to GHRH, probably by inhibiting somatostatin release. The aim of this study was to assess the existence of intraindividual variability in the GH response to GHRH and verify the effects of PD treatment on inter- and intraindividual variability. Twenty normal adults (17 M and 3 F) and 10 normal prepubertal children (9 M and 1 F) underwent 2-5 administrations of 1 micrograms/kg GHRH on different days. Seven adults and all children also underwent 1-5 other tests in which GHRH was preceded (60 min before) by oral PD (120 mg in adults and 60 mg in children). The GH responses to GHRH were highly variable, not only within subjects but also in the same subject on different occasions (peak range; adults: 0.4-49.0 ng/ml; children: 2.4-50.0 ng/ml). PD always markedly increased the GH response to GHRH, even unmasking this response in 3 adults and 4 children hyporesponsive to the neuropeptide alone. However, the variability in the GH response was still present (adults: 27.2-108.5 ng/ml; children: 25.0-144.0 ng/ml), though reduced (adults: p = 0.0005; children: p = 0.0204). These data indicate that: i. A great inter- and intraindividual variability in the GH response to GHRH is present.(ABSTRACT TRUNCATED AT 250 WORDS)