Leptin is a peptide secreted by adipose tissue, which regulates satiety, metabolic rate, and thermogenesis. Since corticosteroids regulate the mass of adipose tissue, and leptin synthesis and secretion by adipocytes, we have examined whether leptin in turn is able to directly affect adrenal steroid secretion. Recombinant murine leptin was found to increase basal aldosterone and corticosterone production by dispersed rat zona glomerulosa and zona fasciculata-reticularis cells, respectively. In contrast, leptin did not affect maximally ACTH (10(-9) M)-stimulated steroid secretion. These findings, coupled with the recent observation that leptin is able to stimulate hypothalamo-pituitary CRH-ACTH system, may indicate a role for leptin as a regulator of adrenocortical function in the rat. (C) 1997 Elsevier Science Ltd. All rights reserved.