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Effects of Short-Term Glucocorticoid Deprivation on Growth Hormone (GH) Response to GH-Releasing Peptide-6: Studies in Normal Men and in Patients with Adrenal Insufficiency¹

Division of Endocrinology, Department of Medicine, Universidade Federal de São Paulo, Universidade Federal de Sao Paulo/Escola Paulista de Medicina, Sao Paulo 04034-970, Brazil

Address all correspondence and requests for reprints to: Dr. Ana-Cláudia de Assis Rocha Pinto, Division of Endocrinology, Escola Paulista de Medicina, Universidade Federal de Sao Paulo, Sao Paulo S.P. 04034-970, C.P. 20266, Brazil. E-mail: ana0292{at}zaz.com.br

There are no data in the literature about the effects of glucocorticoid deprivation on GH-releasing peptide-6 (GHRP-6)-induced GH release. The aims of this study were to evaluate GH responsiveness to GHRP-6 1) after metyrapone administration in normal men, and 2) in patients with chronic hypocortisolism after glucocorticoid withdrawal for 72 h. In normal subjects, metyrapone ingestion did not alter significantly GH responsiveness to GHRP-6 [n = 8; peak, 39.3 ± 7.1 µg/L; area under the curve (AUC), 1958.8 ± 445.7 µg/min·L; mean ± SE] compared to placebo (n = 8; peak, 21.9 ± 4.5; AUC, 1131.0 ± 229.6). In patients with chronic hypocortisolism (n = 8), GH responses to GHRP-6 were similar both during replacement therapy (peak, 11.8 ± 3.9; AUC, 563.2 ± 208.7) and after withdrawal of prednisone (peak, 14.4 ± 4.5; AUC, 695.6 ± 272.9) and did not differ from those in controls. Interestingly, after glucocorticoid withdrawal, GH responsiveness to GHRP-6 in patients with chronic hypocortisolism was significantly lower than that in normal subjects pretreated with metyrapone. Our data suggest that short term glucocorticoid deprivation does not have a major impact on GHRP-6-dependent GH-releasing mechanisms. However, in long standing hypocortisolism, subtle changes in GHRP-6 secretory pathways may be present.