Effect of galanin on growth hormone-releasing hormone-stimulated growth hormone secretion in adult patients with nonendocrine diseases on long-term daily glucocorticoid treatment

Abstract

Glucocorticoids are thought to inhibit growth hormone (GH) secretion through an enhancement of endogenous somatostatin tone. The aim of our study was to evaluate the effect of galanin, a neuropeptide that stimulates GH secretion, on GH-releasing hormone (GHRH)-induced GH secretion in adult patients with nonendocrine diseases who were under daily immunosuppressive glucocorticoid therapy. Six normal subjects (four men, two women) and seven steroid-treated subjects (three men, four women) were studied. GHRH-induced GH secretion was evaluated during a 40-minute intravenous (IV) infusion of saline or porcine galanin (12.5 μg/min). During saline infusion, steroid-treated patients showed a blunted GH response to GHRH (GH peak, 8.1 ± 2.8 μg/L), as compared with normal subjects (GH peak, 23.8 ± 3.9 μg/L). During galanin infusion, the GH response to GHRH was significantly enhanced (GH peak, 46.6 ± 9.4 μg/L, P < .05), as compared with saline infusion in normal subjects. In contrast, galanin infusion did not enhance the GH response to GHRH (GH peak, 16.6 ± 6.5 μg/L), as compared with saline infusion in steroid-treated patients. The area under the GH-response curves was also significantly ( P < .05) lower in steroid-treated subjects, as compared with normal subjects. Thus, galanin failed to normalize or enhance the GH response to GHRH in patients treated long-term with glucocorticoids. It can be hypothesized that galanin does not elicit GH secretion by decreasing hypothalamic somatostatin tone.