EFFECT OF GALANIN AND ARGININE, ALONE OR IN COMBINATION, ON GROWTH-HORMONE SECRETION IN ADULT PATIENTS TREATED WITH GLUCOCORTICOIDS

Glucocorticoids are known to decrease growth hormone (GH) secretion in man. Galanin, a 29-amino acid peptide, and arginine stimulate GH secretion through different hypothalamic mechanisms. The aim of our study was to investigate the effect of arginine and galanin (alone or in combination) on GH secretion in 7 adult patients with nonendocrine diseases receiving chronic daily immunosuppressive glucocorticoid treatment (5 F, 2 M; mean age 48.4 +/- (SEM) 3.7 years). Five normal adults (3 F, 2 M; mean age 34.6 +/- 2.2 years) served as controls. All subjects underwent in random order: (1) infusion of arginine hydrochloride (30 g i.v. in 100 ml saline) from - 30 to 0 min; (2) infusion of synthetic porcine galanin (500 mug i.v. in 100 ml saline) from - 15 to 30 min; (3) intravenous infusion of arginine hydrochloride from -30 to 0 min combined with synthetic porcine galanin from - 15 to 30 min. In normal subjects GH peak after arginine (8.6 +/- 3.3 mug/1) and galanin (6.6 +/- 3.2 mug/1) did not show significant differences; the GH peak after arginine + galanin (21.4 +/- 6.1 mug/1) was significantly higher with respect to galanin or arginine alone. In glucocorticoid-treated patients the GH peak after arginine (4.6 +/- 1.5 mug/1) was significantly (p < 0.05) higher with respect to galanin (1.8 +/- 1.0 mug/1); after arginine + galanin the GH peak (8.2 +/- 2.3 mug/1) was significantly (p < 0.05) enhanced with respect to either galanin or arginine alone. The GH response to arginine was not significantly different in normal and glucocorticoid-treated patients. Normal subjects showed higher GH peaks after galanin alone and arginine + galanin with respect to the steroid-treated group. Moreover, we hypothesize that the inhibitory action of glucocorticoids on GH secretion in man is mediated not only by an increase in somatostatin tone but also by a decrease in endogenous hypothalamic GHRH release.