ARGININE NORMALIZES THE GROWTH-HORMONE (GH) RESPONSE TO GH-RELEASING HORMONE IN ADULT PATIENTS RECEIVING CHRONIC DAILY IMMUNOSUPPRESSIVE GLUCOCORTICOID THERAPY

Glucocorticoids are thought to inhibit GH secretion through an enhancement of endogenous somatostatin tone. The aim of our study was to evaluate the effect of arginine, a secretagogue that increases GH secretion acting at the hypothalamic level, probably by decreasing somatostatin tone, on GH-releasing hormone (GHRH)-induced GH secretion in three male and five female adult patients with nonendocrine diseases who were receiving daily immunosuppressive glucocorticoid therapy. Six normal subjects (four males and two females) served as controls. GHRH-induced GH secretion was evaluated after 30-min iv infusion of saline (100 mL) or arginine (30 g) in 100 mL saline. After saline administration, steroid-treated patients showed a blunted GH response to GHRH (GH peak, 8.7 +/- 2.4-mu-g/L) compared to that of normal subjects (GH peak, 23.8 +/- 3.9-mu-g/L). The GH responses to GHRH increased (P < 0.05) after pretreatment with arginine compared to saline pretreatment in both normal subjects (GH peak, 36.6 +/- 4.0-mu-g/L) and steroid-treated patients (GH peak, 28.4 +/- 5.5-mu-g/L). The GH responses to GHRH plus arginine were not significantly different in steroid-treated and normal subjects. Thus, arginine is able to normalize the GH response to GHRH in patients receiving chronic glucocorticoid treatment. Our data are evidence that the stimulatory action of arginine and the inhibitory action of glucocorticoids on GH secretion are mediated by opposite effects on hypothalamic somatostatin tone.