Evidence for the involvement of nitric oxide in the control of steroid secretion by the frog adrenal gland

Nitric oxide (NO) has been found to modulate the response of rat, bovine an d human adrenocortical cells to corticotropic factors. The aim of the prese nt study was to investigate the possible involvement of NO in the control o f corticosteroid secretion in the frog Rana ridibunda. Histochemical studie s using the NADPH-diaphorase reaction and immunohistochemical labeling with antibodies against NO synthase (NOS) revealed that NOS is exclusively expr essed in chromaffin cells. The NO donor sodium nitroprusside (SNP) and the NO synthase inhibitor Nw-nitro-L-arginine (L-NO,Arg) did not modify the spo ntaneous production of corticosterone and aldosterone by perifused adrenal slices. Similarly, L-NO(2)Arg had no effect on the secretory responses indu ced by ACTH, angiotensin II (AII) and endothelin-1 (ET-1). In contrast, SNP significantly inhibited the stimulatory effects of ACTH, AII and ET-1 on c orticosterone and aldosterone secretion. These data provide the first evide nce for a modulatory role of NO on adrenocortical cell activity in amphibia ns. (C) 2001 Elsevier Science Ltd. All rights reserved.