EXPERIMENTAL STUDY Effect of leptin on ACTH-stimulated secretion of cortisol in rhesus macaques and on human adrenal carcinoma cells Joaquin Lado-Abeal, James J Mrotek 1 , Douglas M Stocco and Reid L Norman Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA and 1 Anatomy and Physiology, Meharry Medical College, Nashville, Tennessee 37208, USA (Correspondence should be addressed to R L Norman, Cell Biologyand Biochemistry, Texas Tech University Health Sciences Center, 3601 4th Street, Lubbock, Texas 79430, USA; Email: reid.norman@ttmc.ttuhsc.edu) Abstract Objective: Because glucocorticoids stimulate leptin release and, at least in vitro, leptin inhibits cortisol secretion, a feedback system between glucocorticoids and leptin has been proposed. However, in humans and non-human primates there are no in vivo studies to support any role for leptin in the control of the hypothalamic–pituitary–adrenal axis. In this study, we investigated the effect of leptin on (i) ACTH-stimulated secretion of cortisol in six male rhesus monkeys and (ii) basal and forskolin (FSK)-stimulated cortisol secretion by the human adrenal carcinoma cell H295R in vitro. Design and Methods: In vivo studies: after suppression of endogenous ACTH with either dexamethasone (n = 6) or a corticotropin-releasing factor (CRF) antagonist (D-Phe CRF(12–41)) (n = 3), 1 mg bolus of human ACTH(1–24) was administered to stimulate adrenal cortisol release. Blood samples were collected every 15 min for 3 h. Leptin (1 mg) was infused over 4 h, starting 1 h before ACTH bolus. In vitro studies: NCI-H295R cells were incubated for 6, 12, 24 and 48 h in the absence or presence of 20 mmol/l FSK in combination with leptin (100 ng/ml medium). Cortisol levels in serum and medium were measured by solid phase radioimmunoassay. Results: Acute leptin infusion to rhesus monkeys did not change basal cortisol levels, peak cortisol levels after ACTH(1–24) or the area under the curve when compared with studies in which leptin was not given. FSK increased cortisol levels in medium at 24 and 48 h, but leptin did not change cortisol release in either control or FSK-stimulated cells. Conclusions: Short-term leptin infusion affected neither the cortisol response to ACTH in non-human primates in vivo nor cortisol release (basal or FSK stimulated) by H295R cells, in vitro. These data suggest that leptin may not be an acute regulator of primate adrenal cortisol secretion. European Journal of Endocrinology 141 534–538 Introduction Glucocorticoids participate in the control of caloric intake and adipogenesis. In patients who have elevated gluco- corticoids such as in Cushing’s disease, obesity or weight gain is observed in 79–95% of the affected individuals (1). Glucocorticoids also stimulate food intake (2), synthesis and activity of the adipose tissue lipoprotein lipase (3) and adipocyte differentiation and distribution (4, 5). Some of these actions are in synergism with insulin (6, 7). Glucocorticoids also participate in epinephrine synthesis in the adrenal medulla (8) and both epinephrine and insulin influence energy metabolism. In mouse and rat experimental models, obesity does not progress after adrenalectomy (9). In the ob/ob mouse, obesity is caused by a mutation in the gene for leptin (10), a protein that influences energy intake and expenditure (11) at both central (12) and peripheral sites (13, 14). Glucocorticoids stimulate the synthesis and release of leptin in rodents and humans (15–18) and reciprocally, the hyperglucocorticoidemia observed in ob/ob mice is reduced with leptin administration (19). Leptin blocks HPA axis activation in restrained mice and, depending on the circumstances, can block corticotropin-releasing hormone (CRH) release in vitro (20). Leptin also decreases basal cortisol release by bovine adrenal cells (21) and adrenocorticotropin (ACTH)-stimulated cortisol release by bovine (21) and human adrenal cells (22) in vitro. Together, these data suggest an inhibitory feedback action of leptin on the hypothalamic–pituitary–adrenal axis. The two objectives of this study were to determine if leptin affects ACTH-stimulated secretion of cortisol in rhesus monkeys in vivo and to determine if leptin alters cortisol secretion by human adrenal carcinoma cells in vitro. European Journal of Endocrinology (1999) 141 534–538 ISSN 0804-4643 q 1999 Society of the European Journal of Endocrinology Online version via http://www.eje.org