Leptin Inhibits Directly Glucocorticoid Secretion by Normal Human and Rat Adrenal Gland* * This work was supported by a grant from the Swiss National Science Foundation (No. 3100-050748.97/1).

Different interactions have been described between glucocorticoids and the product of the ob gene leptin. Leptin can inhibit the activation of the hypothalamo-pituitary-adrenal axis by stressful stimuli, whereas adrenal glucocorticoids stimulate leptin production by the adipocyte. The present study was designed to investigate the potential direct effects of leptin to modulate glucocorticoid production by the adrenal. Human adrenal glands from kidney transplant donors were dissociated, and isolated primary cells were studied in vitro. These cells were preincubated with recombinant leptin (10–10 M) for 6 or 24 h, and basal or ACTH-stimulated cortisol secretion was subsequently measured. Basal cortisol secretion was unaffected by leptin, but a significant and dose-dependent inhibition of ACTH-stimulated cortisol secretion was observed [down by 29 6 0.1% of controls with the highest leptin dose, P , 0.01 vs. CT (unrelated positive control)]. This effect of leptin was also observed in rat primary adrenocortical cells, where leptin inhibited stimulated corticosterone secretion in a dose-dependent manner (down by 46 6 0.1% of controls with the highest leptin dose, P , 0.001 vs. CT). These effects of leptin in adrenal cells are likely mediated by the long isoform of the leptin receptor (OB-R), because its transcript was found to be expressed in the adrenal tissue and leptin had no inhibitory effect in adrenal glands obtained from db/db mice. Therefore, leptin inhibits directly stimulated cortisol secretion from human and rat adrenal glands, and this may represent an important mechanism to modulate glucocorticoid levels in various metabolic states. (Endocrinology 139: 4264– 4268, 1998) A glucocorticoid hormones are key regulators of several metabolic pathways, under normal conditions and during the response to stressful stimuli. At low concentrations, corticosterone (or cortisol) is anabolic, stimulating feeding and promoting normal fat and protein storage (1–3). In addition to their physiological effects, glucocorticoids play a critical permissive role in the pathogenesis of the experimental hypothalamic obesity syndrome (4). These deleterious effects played by corticosterone in the development of obesity have also been demonstrated in the genetically obese fatty Zucker rat, where the obese phenotype can be prevented by adrenalectomy (1). Finally, at high doses (5) or in diabetic animals in which insulin may not play its counterregulatory effects on food intake (3), glucocorticoids seem to participate in excessive fat storage, as well as in insulin resistance. The secreted product of the adipocyte leptin (6) also participates in the regulation of metabolism and food intake, at least partially, by modulating the expression of the hypothalamic orexigenic peptide neuropeptide Y (7). Several other neuroendocrine effects of leptin have been described, including a down-regulation of the fasting-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis (8). Therefore, changes in the nutritional or metabolic status of the organism, as reflected by changes in circulating leptin levels, can ultimately modulate the production of cortisol, a hormone with numerous metabolic functions. These effects are mediated, in part, by the lowering of ACTH secretion induced by leptin (8). However, recent data suggest that leptin could also have direct effects on the endocrine pancreas (9–11), as well as on ovarian granulosa cells (12, 13). In the present study, we have tested the hypothesis that, in addition to its central nervous system (CNS) effects, leptin may have direct effects in the control of glucocorticoid secretion by the adrenal gland. We have demonstrated that leptin exerts a direct, dose-dependent inhibition of stimulated cortisol secretion by normal human adrenal cells in vitro and that a similar inhibition was also present in normal rat adrenocortical cells in primary culture. This effect is likely mediated by the active isoform of the leptin receptor, OB-Rb (14, 15), because its expression could be demonstrated in human adrenal tissue. Materials and Methods Human adrenal culture Normal human adrenals (n 5 3) were obtained from cadaveric kidney transplant donors. They were dissected from the kidney before its transplantation to the receiver, and adrenal cells were immediately dispersed as described previously (16). Briefly, adrenals were minced with a scalpel blade, and then subjected Received December 1, 1997. Address all correspondence and requests for reprints to: François P. Pralong, M.D., Division of Endocrinology, Diabetology and Metabolism, Department of Medicine, BH 19707, Centre Universitaire Vaudois, 1011 Lausanne, Switzerland. E-mail: francois.pralong@chuv.hospvd. ch. * This work was supported by a grant from the Swiss National Science Foundation (No. 3100–050748.97/1). † Recipient of a Research Development Carrier Award from the Prof. Dr. Max Cloëtta Foundation. ‡ Recipient of a Research Development Carrier Award from the Swiss National Science Foundation (No. 32–49673.96). 0013-7227/98/$03.00/0 Vol. 139, No. 10 Endocrinology Printed in U.S.A. Copyright © 1998 by The Endocrine Society