Role of the atrial natriuretic peptide for adrenal regulation in the teleost fish Cyprinus carpio.

Abstract

The biological role of atrial natriuretic peptide (ANP) for the adrenal tissue of the teleost fish Cyprinus carpio, the carp, was investigated using in vitro autoradiography to study ANP binding sites, immunohistochemistry to localize ANP-like peptides, and in vitro perifusion to measure adrenal cortisol and catecholamine release. 125I-labeled rat ANP-(99-126) [125I-rANP-(99-126)] binding was present in adrenal tissue exhibiting positive cooperativity with a half-maximal binding concentration (EC50) of 87 +/- 15 pM and a maximal binding capacity (Bmax) of 56 +/- 11 amol/mm2 (n = 3). 125I-rANP-(99-126) binding was competitively displaced by unlabeled ANP analogues with an intact disulfide bridge showing a lower affinity than the iodinated ligand. By the use of immunohistochemistry, ANP immunoreactivity was found in the majority of the phenylethanolamine N-methyl-transferase-immunoreactive, i.e., epinephrine-synthesizing cells. In vitro, ANP elevated both basal and acetylcholine-stimulated cortisol release by carp adrenal tissue, whereas adrenal catecholamines were significantly affected only in acetylcholine-stimulated epinephrine secretion. Thus ANP derived from the ANP-immunoreactive chromaffin cells of the carp adrenal seems to act in an autocrine and/or paracrine manner on steroidogenic interrenal and catecholaminergic chromaffin cells. Furthermore, the study indicates that the ANP effects on fish catecholamine and steroid release are reversed in mammals.