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Different growth hormone (GH) response to GH-releasing peptide and GH-releasing hormone in hyperthyroidism.

Abstract
Altered GH responses to several pharmacological stimuli, including GHRH, have been found in hyperthyroidism. The mechanisms underlying these disturbances have not been fully elucidated. GH-releasing peptide-6 (GHRP-6) is a synthetic hexapeptide that specifically stimulates GH release both in vitro and in vivo. The mechanism of action of GHRP-6 is unknown, but it probably acts by inhibiting the effects of somatostatin on GH release. The aim of this study was to evaluate the effects of GHRP-6 on GH secretion in patients with hyperthyroidism (n = 9) and in control subjects (n = 9). Each subject received GHRP-6 (1 microg/kg, iv), GHRH (100 microg, iv), and GHRP-6 plus GHRH on 3 separate days. GH peak values (mean +/- SE; micrograms per L) were significantly lower in hyperthyroid patients compared to those in control subjects after GHRH alone (9.0 +/- 1.3 vs. 27.0 +/- 5.2) and GHRP-6 plus GHRH (22.5 +/- 3.5 vs. 83.7 +/- 15.2); a lack of the normal synergistic effect of the association of both peptides was observed in thyrotoxicosis. However, a similar GH response was seen in both groups after isolated GHRP-6 injection (31.9 +/- 5.7 vs. 23.2 +/- 3.9). In summary, we have shown that hyperthyroid patients have a normal GH response to GHRP-6 together with a blunted GH responsiveness to GHRH. Our data suggest that thyroid hormones modulate GH release induced by these two peptides in a differential way.
AuthorsJ C Ramos-Dias, F Pimentel-Filho, A F Reis, A M Lengyel
JournalThe Journal of clinical endocrinology and metabolism (J Clin Endocrinol Metab) Vol. 81 Issue 4 Pg. 1343-6 (Apr 1996) ISSN: 0021-972X [Print] UNITED STATES
PMID8636330 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)
Chemical References
  • Oligopeptides
  • growth hormone releasing hexapeptide
  • Growth Hormone
  • Growth Hormone-Releasing Hormone
Topics
  • Adult
  • Analysis of Variance
  • Drug Interactions
  • Female
  • Graves Disease (blood, physiopathology)
  • Growth Hormone (blood, secretion)
  • Growth Hormone-Releasing Hormone (administration & dosage)
  • Humans
  • Injections, Intravenous
  • Kinetics
  • Oligopeptides (administration & dosage)
  • Reference Values
  • Time Factors

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