Decreased ghrelin-induced GH release in thyrotoxicosis: comparison with GH-releasing peptide-6 (GHRP-6) and GHRH.
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.
Nascif
Sergio Oliva
SO
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
Correa-Silva
Silvia Regina
SR
Silva
Marcos Roberto
MR
Lengyel
Ana-Maria Judith
AM
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*
D001786:Blood Glucose; D054439:Ghrelin; D009842:Oligopeptides; D019382:Human Growth Hormone; C041048:growth hormone releasing hexapeptide; D013007:Growth Hormone-Releasing Hormone