title: Decreased ghrelin-induced GH release in thyrotoxicosis: comparison with GH-releasing peptide-6 (GHRP-6) and GHRH.
abstract: In thyrotoxicosis GH response to several stimuli is impaired, but there is no data on ghrelin-induced GH release in these patients. Ghrelin is a potent GH secretagogue and it also increases glucose levels in men. The aim of this study was to evaluate the effects of ghrelin (1 microg/kg), GHRP-6 (1 mug/kg) and GHRH (100 microg), i.v., on GH levels in 10 hyperthyroid patients and in 8 controls. Glucose levels were also measured during ghrelin and GHRP-6 administration. In control subjects and hyperthyroid patients peak GH (microg/l; mean +/- SE) values after ghrelin injection (controls: 66.7 +/- 13.6; hyper: 19.3 +/- 2.4) were significantly higher than those obtained after GHRP-6 (controls: 26.7 +/- 5.1; hyper: 12.6 +/- 1.3) and GHRH (controls: 13.5 +/- 4.3; hyper: 5.3 +/- 1.3). There was a significant decrease in GH responsiveness to ghrelin, GHRP-6 and GHRH in the hyperthyroid group compared to controls. In control subjects and hyperthyroid patients basal glucose (mmol/l) values were 4.5 +/- 0.1 and 4.7 +/- 0.2, respectively. There was a significant increase in glucose levels 30 min after ghrelin injection (controls: 4.9 +/- 0.1; hyper: 5.2 +/- 0.2), which remained elevated up to 120 min. When the two groups were compared no differences in glucose values were observed. GHRP-6 administration was not able to increase glucose levels in both groups. Our data shows that GH release after ghrelin, GHRP-6 and GHRH administration is decreased in thyrotoxicosis. This suggests that thyroid hormone excess interferes with GH-releasing pathways activated by these peptides. Our results also suggest that ghrelin's ability to increase glucose levels is not altered in thyrotoxicosis.
authors.affiliation: Division of Endocrinology, Universidade Federal de São Paulo, UNIFESP/EPM, Rua Pedro de Toledo, 910, 04039-002 São Paulo, SP, Brazil. snascif@uol.com.br
authors.forename: Sergio Oliva
authors.initials: SO
authors.lastname: Nascif
authors.forename: Silvia Regina
authors.initials: SR
authors.lastname: Correa-Silva
authors.forename: Marcos Roberto
authors.initials: MR
authors.lastname: Silva
authors.forename: Ana-Maria Judith
authors.initials: AM
authors.lastname: Lengyel
mesh_terms: D001786:Blood Glucose / Q000378:metabolism; D054439:Ghrelin / Q000009:adverse effects; D013007:Growth Hormone-Releasing Hormone; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D009842:Oligopeptides / Q000009:adverse effects; D013971:Thyrotoxicosis / Q000503:physiopathology*
chemical_list: D001786:Blood Glucose; D054439:Ghrelin; D009842:Oligopeptides; D019382:Human Growth Hormone; C041048:growth hormone releasing hexapeptide; D013007:Growth Hormone-Releasing Hormone