P-071. Effects of hexarelin alone or in combination with TRH on

Aim of the present paper is to verify whether a modification of the somatostatinergic tone is induced by the GH-releasing peptide, hexarelin (HEX). As somatostatin, apart from GH, is inhibitory on TSH secretion, we studied its effects on TRH-induced TSH secretion. Seven normal subjects (4 women and 3 men aged 24-29 years) underwent the following tests on 3 different day: (a) TRH (200 μg/L i.v.) + placebo (P); (b) HEX (1 μg/Kg bw i.v.) + placebo (P) (c) combined TRH + HEX administration. Serum TSH and GH were measured by ultra-sensitive IFMAs. The responses to tests were evaluated as AUC calculated by trapezoidal method and were compared by a non-parametric method (Wilcoxon signed-rank). A significant increase in serum GH levels occurred after HEX administration, when given in combination either with P or with TRH (1217 × 470 vs 986±208 μg/min/L, p:NS), while no modifications of GH levels were seen after TRH + P. Serum TSH levels were unmodified by HEX injection. The increase elicited by TRH + HEX was similar to that elicited by TRH alone (1124±530 vs 1273±380 mU/min/L, p:NS). In conclusion: HEX administration did not modify basal and TRH-stimulated TSH secretion, thus suggesting that the GH-releasing effect of hexarelin is somatostatin-independent.