Growth hormone responses to GH-releasing peptide (GHRP-6) in hypothyroidism.
Clin Endocrinol (Oxf)
; 46(3): 295-300, 1997 Mar.
Article
em En
| MEDLINE
| ID: mdl-9156038
OBJECTIVE: Both spontaneous and stimulated GH secretion are reduced in patients with hypothyroidism. The mechanisms involved in these alterations are not yet fully understood. GHRP-6 is a synthetic hexapeptide that releases GH both in vivo and in vitro. Its mechanism of action is unknown, but there is evidence that this peptide acts as a functional somatostatin antagonist at pituitary level. The aim of this study was to evaluate the GH response to GHRP-6 in patients with primary hypothyroidism and in normal controls. DESIGN: Patients with hypothyroidism and normal controls were randomly submitted to 3 tests with GHRH (100 micrograms i.v.), GHRP-6 (1 microgram/kg i.v.) and GHRH + GHRP-6, on separate days. PATIENTS: Eleven patients with primary hypothyroidism were compared with 10 control subjects. MEASUREMENTS: GH, TSH and free T4 were measured by immunofluorometric assay and IGF-1 by radioimmunoassay. RESULTS: Hypothyroid patients had markedly lower peak GH values (mean +/- SE micrograms/l) after GHRH administration (4.1 +/- 0.9) compared to control subjects (24.9 +/- 5.1). After GHRP-6 injection hypothyroid patients had a significantly higher GH release (12.6 +/- 1.9) than that obtained with GHRH, while in control subjects GH values were similar (22.1 +/- 3.6). No significant differences in peak GH responses were observed following the administration of either GHRP-6 alone (controls 22.1 +/- 3.6; patients 12.6 +/- 1.9) or in combination with GHRH (controls 77.4 +/- 15.0; patients 52.8 +/- 10.9), despite the trend to smaller responses in hypothyroid patients. CONCLUSION: We have shown that patients with primary hypothyroidism have higher GH responses to GHRP-6 than to GHRH, which are markedly blunted. When GHRP-6 was associated with GHRH, a significant increase in the GH response was observed in these patients, which could suggest a role for somatostatin in this process. Our data suggest that thyroid hormones modulate GH release induced by GHRH and GHRP-6 through different mechanisms. However, additional studies are necessary to further elucidate this hypothesis.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Oligopeptídeos
/
Hormônio do Crescimento
/
Hormônio Liberador de Hormônio do Crescimento
/
Hipotireoidismo
Tipo de estudo:
Clinical_trials
Limite:
Adult
/
Female
/
Humans
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Male
/
Middle aged
Idioma:
En
Revista:
Clin Endocrinol (Oxf)
Ano de publicação:
1997
Tipo de documento:
Article
País de afiliação:
Brasil
País de publicação:
Reino Unido