Receptors for atrial natriuretic factor (ANF) in kidney and adrenal tissue of urodeles--lack of angiotensin II (A II) receptors in these tissues.

Binding sites for atrial natriuretic factor (ANF) and angiotensin II (A II) were localized and quantified in renal and adrenal tissue of the Urodele Ambystoma mexicanum by quantitative in vitro autoradiography using 125I-ratANF(99-126) and 125I-[Val5]-A II or 125I-human A II as labeled ligands. Specific 125I-ratANF(99-126) binding was present in glomeruli, renal tubules, and adrenal tissue. ANF had heterogeneous binding sites exhibiting positive cooperativity with a half maximal binding concentration (EC50) of 124 +/- 12 pM in glomeruli and 118 +/- 18 pM in adrenal tissue (n = 8). The corresponding maximal binding capacities (Bmax) were 0.84 +/- 0.10 and 0.72 +/- 0.18 femtomol/mm2. 125I-ratANF(99-126) binding was competitively displaced by unlabeled ANF analogues with an intact disulfide bridge showing a lower affinity than the iodinated ligand. In in vitro perifusion experiments ANF inhibited basal as well as ACTH-stimulated steroid secretion whereas catecholamine release was not affected indicating that ANF binding in adrenal tissue is restricted to steroidogenic interrenal cells. In vivo experiments demonstrated that during acclimation to 1.5% salt water made using seawater salt the number of ANF binding sites in kidney glomeruli decreased after 12 hr and 7 days while no significant changes were observed in adrenal tissue. No A II binding sites were detected either in renal or adrenal tissue indicating a lack of A II receptors in these tissues, which was confirmed by in vitro perifusion experiments which showed that A II did not affect adrenal steroid and catecholamine secretion.