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E Ghigo, E Arvat, G Rizzi, S Goffi, S Grottoli, M Mucci, MF Boghen and F Camanni

Ghigo E, Arvat E, Rizzi G, Goffi S, Grottoli S, Mucci M, Boghen MF, Camanni F. Growth hormonereleasing activity of growth hormone-releasing peptide-6 is maintained after short-term oral pretreatment with the hexapeptide in normal aging. Eur J Endocrinol 1994;131:499–503. ISSN 0804–4643

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 μg/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 μg/kg iv) also was studied. Before treatment, oral administration of 300 μg/kg GHRP-6 elicited a clear GH rise (peak 10.7 ± 3.3 μg/l; AUC 353.1 ± 90.6 μg·l−1·h−1). which was significantly higher (p < 0.01) than that induced by intravenous GHRH (peak 5.1 ± 1.5 μg/l; AUC 106.5 ±43.9 μg · 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 μg/l; AUC 499.8 ± 107.2 μg·l−1·h−1). The IGF-I levels were not increased significantly after treatment (77.1 ± 8.4 vs 84.1 ± 12.2 μg/l). In conclusion, our results demonstrate that, in aging, oral GHRP-6 administration elicits a GH response that is higher than the maximal effective dose of intravenous GHRH and that the effect of the hexapeptide does not vanish after short-term treatment. More prolonged treatment and/or more frequent administrations of GHRP-6 are likely needed to increase IGF-I levels.

F Camanni, Division of Endocrinology, Department of Pathophysiology, Ospedale Molinette, C.so Dogliotti 14, 10126 Torino, Italy

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M Maccario, JD Veldhuis, F Broglio, LD Vito, E Arvat, R Deghenghi and E Ghigo

OBJECTIVE: To extend the insights on the action of GH secretagogues (GHS) on pituitary function, we studied the impact of intermittent daily s.c. administration of a peptidyl GHS, hexarelin (HEX), on 24-h GH, PRL, ACTH and cortisol release in healthy volunteers. DESIGN: We investigated the impact of two or three times daily s.c. administration of a short-acting peptidyl GHS, the hexapeptide HEX (1.5 microg/kg) on 24-h GH, PRL, ACTH and cortisol secretion (sampling every 20 min) in six normal young men. To monitor possible down-regulation, the effect of 1 microg/kg i.v. HEX at the end of each 24-h sampling period was studied. METHODS: Multi-parameter deconvolution analysis was used to quantitate pulsatile GH, PRL, ACTH and cortisol secretion and estimate the corresponding hormone half-lives. Complementary to deconvolution analysis, approximate entropy was used as a scale- and model-independent statistic to quantify the serial orderliness or pattern regularity of hormone measurements. RESULTS: Mean and integrated (24-h) serum GH concentrations were increased from baseline values to the same extent by two and three HEX injections. Both HEX schedules equally increased GH secretory burst mass (but not burst frequency), mean daily GH production rate, GH half-life and irregularity of GH release patterns. No change occurred in the secretion of IGF-I, PRL, ACTH and cortisol. Intravenous HEX at the end of each spontaneous 24-h profile induced a significant rise in GH, PRL, ACTH and cortisol. Prior HEX administration blunted the GH response, abolished that of ACTH and cortisol and did not modify the PRL increase. CONCLUSIONS: The study showed that two or three daily s.c. injections of HEX augmented 24-h GH secretion equally, amplifying selectively GH secretory pulse mass without altering lactotroph and corticotroph secretion. IGF-I levels were not modified by these 1-day HEX treatment schedules.

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E. Ghigo, E. Ciccarelli, S. D. Bianchi, G. Gatti, G. M. Molinatti, F. Massara, E. E. Müller and F. Camanni

Abstract. 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.

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E. Ghigo, S. Goffi, E. Arvat, M. Nicolosi, M. Procopio, J. Bellone, E. Imperiale, E. Mazza, G. Baracchi and F. Camanni

Abstract.

In 11 elderly normal subjects and in 17 young healthy subjects we studied the response of plasma growth hormone to GH-releasing hormone (GHRH(29), 1 μg/kg iv) alone and preceded by pyridostigmine ( 120 mg orally 60 min before GHRH), a cholinesterase inhibitor likely able to suppress somatostatin release. The GH response to pyridostigmine alone was also examined. Basal plasma GH levels were similar in elderly and young subjects. In the elderly, GHRH induced a GH rise (AUC, median and range: 207.5, 43.5-444.0 μg · 1−1 · h−1) which was lower (p = 0.006) than that observed in young subjects (548.0, 112.5-2313.5 μg · 1−1 · h−1). The pyridostigmine-induced GH rise in the elderly was similar to that in young subjects (300.5, 163.0-470.0 vs 265.0, 33.0-514.5 μg · 1−1 · h−1). Pyridostigmine potentiated the GH responsiveness to GHRH in both elderly (437.5, 152.0-1815.5 μg · 1−1 · h−1; p = 0.01 vs GHRH alone) and young subjects (2140.0, 681.5-4429.5 μg · 1−1 · h−1; p = 0.0001 vs GHRH alone). However, the GH response to pyridostigmine + GHRH was significantly lower (p = 0.0001) in elderly than in young subjects. In conclusion, the cholinergic enhancement by pyridostigmine is able to potentiate the blunted GH response to GHRH in elderly subjects, inducing a GH increase similar to that observed after GHRH alone in young adults. This finding suggests that an alteration of somatostatinergic tone could be involved in the reduced GH secretion in normal aging. However, a decreased GH response to combined administration of pyridostigmine and GHRH in elderly subjects suggests that other abnormalities may coexist, leading to the secretory hypoactivity of somatotropes.

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P Cassoni, C Ghe, T Marrocco, E Tarabra, E Allia, F Catapano, R Deghenghi, E Ghigo, M Papotti and G Muccioli

BACKGROUND: Ghrelin, a natural growth hormone secretagogue (GHS), has been identified in prostate carcinoma cell lines. OBJECTIVES: To investigate the presence of ghrelin and its receptors in human prostate tumours and in DU-145, PC-3 and LNCaP prostate carcinoma cell lines, and to assess the effects of ghrelin and its more abundant circulating form, des-octanoyl ghrelin, on cell proliferation. METHODS: Ghrelin and types 1a and 1b GHS receptor (GHS-R) were determined at the mRNA and protein levels by RT-PCR, in situ hybridization, immunohistochemistry and enzyme immunoassay in tissues, cell lines and culture medium. Ghrelin binding was determined by radioreceptor assay. The effects on cell proliferation were evaluated by growth curves. RESULTS: Ghrelin mRNA was found in prostatic carcinomas and benign hyperplasias, but immunohistochemistry was negative. GHS-R1a and 1b mRNAs were absent from carcinomas, but GHS-R1b mRNA was present in 50% of hyperplasias. Ghrelin peptide and mRNA were present in PC-3 cells exclusively, whereas GHS-R1a and 1b mRNAs were expressed in DU-145 cells only. Specific [125I]Tyr4-ghrelin binding was detected in prostate tumour, DU-145 and PC-3 cell membranes and the binding was displaced by ghrelin, synthetic GHS and des-octanoyl ghrelin, which is devoid of GHS-R1a binding affinity and GH-releasing activity. Ghrelin and des-acyl ghrelin inhibited DU-145 cell proliferation, displayed a biphasic effect in PC-3 cells and were ineffective in LNCaP cells. CONCLUSIONS: Specific GHS binding sites, other than GHS-R1a and 1b, are present in human prostatic neoplasms. Ghrelin, in addition to des-acyl ghrelin, exerts different effects on cell proliferation in prostate carcinoma cell lines.

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E Arvat, J Ramunni, J Bellone, L Di Vito, C Baffoni, F Broglio, R Deghenghi, E Bartolotta and E Ghigo

Hexarelin (HEX) is a synthetic growth hormone-releasing peptide (GHRP) which acts on specific receptors at both the pituitary and the hypothalamic level to stimulate GH release in an age-dependent manner. Like other GHRPs, HEX possesses also prolactin (PRL) and ACTH/cortisol-releasing activity. similar to that of human corticotropin-releasing hormone (hCRH). The mechanisms underlying the stimulatory effect of GHRPs on lactotrope and corticotrope secretion are even less clear and the influence of age on these endocrine activities of GHRPs is unknown. To clarify this point we studied the GH, PRL, ACTH and cortisol responses to the maximal effective dose of HEX (2.0 micrograms/kg i.v.) in: 12 prepubertal children (Pre-C, 8 male, 4 female, age 5.8-12.1 years); 12 pubertal normal short children (Pub-C, 5 male, 7 female, age 9.7-15.5 years, pubertal stage II-IV); 20 normal young adults (Young, 6 males, 14 females, age 23-32 years); and in 16 normal elderly people (Elderly, 5 male, 11 female, age 66-81 years). The GH response to HEX was clear in Pre-C (0-120 min area under curve, mean +/- S.E.M. 769.5 +/- 122.2 micrograms*min/l) but strikingly increased (P < 0.001) in Pub-C (1960.2 +/- 283.5 micrograms*min/l). The HEX-induced GH rise in Young (1829.7 +/- 243.1 micrograms*min/l) persisted similar to that in Pub-C, but decreased in Elderly (951.1 +/- 232.9 micrograms*min/I, P < 0.005); the latter was, in turn, similar to that in Pre-C. HEX induced a significant PRL increase which, however, showed no age-related variations, being similar in Pre-C (512.1 +/- 88.0 micrograms*min/l), Pub-C (584.0 +/- 106.0 micrograms*min/l), Young (554.9 +/- 56.0 micrograms*min/l) and Elderly (523.9 +/- 59.6 micrograms*min/l). The ACTH-releasing activity of HEX was present in Pre-C (1356.6 +/- 204.9 pg*min/ml) and was clearly enhanced (P < 0.02) in Pub-C (2253.5 +/- 242.8 pg*min/ml). The ACTH rise after HEX in Young (1258.1 +/- 141.2pg*min/ml) was lower (P < 0.02) than that in Pub-C and similar to that in Pre-C, while the ACTH response to HEX in Elderly (1786.5 +/- 340.1 pg*min/ml) showed a further trend toward increase, being similar to that in Pub-C. On the other hand, the cortisol response to HEX showed no significant age-related variations, being not different in Pre-C (7747.2 +/- 1031.6 micrograms*min/l), Pub-C (6106.0 +/- 862.9 micrograms*min/l), Young (6827.5 +/- 509.6 micrograms*min/I) and Elderly (7950.6 +/- 658.3 micrograms*min/l). In conclusion, our present data demonstrate that in humans the GH- and ACTH-releasing activities of HEX undergo different age-related variations, while its PRL-releasing activity is not dependent on age. These finding suggest that actions at different levels and/or on different receptor subtypes mediate the different age-related hormonal effects of GHRPs.

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Ferdinando Massara, Ezio Ghigo, Pia Molinatti, Enrico Mazza, Vittorio Locatelli, Eugenio E. Müller and Franco Camanni

Abstract. It is known that in normal subjects repeated administrations of the growth hormone-releasing factor (GRF) induces a state of partial refractoriness of the somatotropes to GRF. Studies were conducted to verify whether the cholinergic system plays a role in the mechanism(s) underlying the reduced GH responsiveness to the neuropeptide. In five healthy men, the GH response to three consecutive injections of GRF (50 μg iv), administered at 2 h intervals, was considerably blunted after the second and third GRF bolus. Administration of the inhibitor of cholinesterase, pyridostigmine bromide (120 mg orally) 30 min before the second GRF bolus, not only restored but greatly potentiated the GH responsiveness to the second GRF bolus. The GH response to the third GRF bolus was not apparently influenced by pre-treatment with pyridostigmine. These data reinforce the view that cholinergic neurotransmission plays an important role in the control of GH secretion in human.

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J Bellone, L Ghizzoni, G Aimaretti, C Volta, MF Boghen, S Bernasconi and E Ghigo

Bellone J, Ghizzoni L, Aimaretti G, Volta C, Boghen MF, Bernasconi S, Ghigo E. Growth hormonereleasing effect of oral growth hormone-releasing peptide 6 (GHRP-6) administration in children with short stature. Eur J Endocrinol 1995;133:425–9. ISSN 0804–4643

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 μg/kg) was compared with that of the maximally effective dose of intravenous GH-releasing hormone (GHRH-29, 1 μg/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 μg/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 μg/l, p < 0.0006; area under curve: 1527.3 ± 263.9 μgl−1 h) which was similar to that elicited by GHRH (peak at 45 min vs baseline: 20.8 ±4.5 vs 2.2±0.9 μg/l, p <0.007; area under curve: 1429.4 ± 248.2 μgl−1 h−1). In a second group of children (N = 6), the GH response to oral GHRP-6 administration (peak at 75 min vs baseline: 18.5 ±5.1 vs 1.5 ± 0.6 μg/l, p < 0.01; area under curve: 1598.5 ± 289.3 μgl−1 h−1) was not modified by co-administration of oral ARG (peak at 90 min vs baseline: 15.2 ±5.6 vs 0.9±0.3 μg/l, p < 0.002; area under curve: 1327.8 ± 193.2 μgl−1 h−1). The amount of GH released and the timing of the somatotrope response after the oral administration of GHRP-6 were similar in the two groups. In conclusion, the present data show that in normal short children the oral administration of GHRP-6 is able to increase GH secretion to an extent similar to that observed after intravenous administration of the maximally effective GHRH dose. Moreover, in contrast to GHRH, the effect of GHRP-6 is not enhanced by low-dose oral ARG. As this amino acid likely acts via inhibition of hypothalamic somatostatin release, our data suggest that a decrease in the somatostatinergic activity does not improve the GH-releasing effect of GHRP-6 in childhood, at variance with that observed after GHRH. Our results suggest that GHRP-6 could be clinically useful to stimulate GH secretion in short children.

E Ghigo, Divisione di Endocrinologia, Ospedale Molinette, C. so. AM Dogliotti 14, 10126 Torino, Italy

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S Bo, L Gentile, A Castiglione, V Prandi, S Canil, E Ghigo and G Ciccone

Objective

C-peptide, a cleavage product of insulin, exerts biological effects in patients with type 1 diabetes mellitus, but its role in type 2 diabetes mellitus is controversial. Our aim was to examine the associations between fasting C-peptide levels and all-cause mortality, specific-cause mortality and the incidence of chronic complications in patients with type 2 diabetes.

Design

Retrospective cohort study with a median follow-up of 14 years.

Methods

A representative cohort of 2113 patients with type 2 diabetes mellitus and a subgroup of 931 individuals from this cohort without chronic complications at baseline from a diabetic clinic were studied.

Results

Patients with higher C-peptide levels had higher baseline BMI and triglyceride and lower HDL-cholesterol values. During the follow-up, 46.1% of the patients died. In a Cox proportional hazard model, after multiple adjustments, no significant association was found between the C-peptide tertiles and all-cause mortality or mortality due to cancer, diabetes or cardiovascular diseases. In the subgroup of 931 patients without chronic complications at baseline, the incidence of microvascular complications decreased from the first to the third C-peptide level tertile, while the incidence of cardiovascular disease did not differ. The risks for incident retinopathy (hazard ratio (HR)=0.33; 95% confidence interval (CI) 0.23–0.47), nephropathy (HR=0.27; 95% CI 0.18–0.38) and neuropathy (HR=0.39; 95% CI 0.25–0.61) were negatively associated with the highest C-peptide tertile, after adjusting for multiple confounders.

Conclusions

Higher baseline C-peptide levels were associated with a reduced risk of incident microvascular complications but imparted no survival benefit to patients with type 2 diabetes mellitus.

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J Bellone, G Aimaretti, MR Valetto, S Bellone, C Baffoni, E Arvat, S Seminara, F Camanni and E Ghigo

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