LOCALIZATION OF ATRIAL-NATRIURETIC-FACTOR RECEPTORS IN THE MESENTERIC ARTERIAL BED - COMPARISON WITH ANGIOTENSIN-II AND ENDOTHELIN RECEPTORS

Although receptors for atrial natriuretic factor (ANF) and angiotensin II (Ang II) have been reported in rat mesenteric arteries, both peptides induce weak biological responses. Endothelin-1 (ET-1) evokes a potent vasoconstriction in the mesenteric artery. To identify the tissue localization of ANF, Ang II, and ET-1 receptors, radioligand binding experiments with I-125-ANF, I-125-[Sar(1),Ile(8)]Ang II, and I-125-ET-1 were performed in defatted mesenteric arteries and in the surrounding adipose tissue. I-125-ANF binding assays in adipose tissue showed a single class of high-affinity binding sites (B-max, 420 +/- 16 fmol/mg protein; K-d, 343 +/- 16 pmol/L). In vascular membranes, most I-125-ANF binding was nonspecific. The majority of receptors present in adipose tissue recognized ANF, C-type natriuretic peptide (CNP), and des-[Gln(18),Ser(19),Gly(20), Leu(21),Gly(22)]ANF-(4-23) (C-ANF) with close affinities, with C-ANF competing for > 98% of the binding sites. In adipocytes, ANF and CNP stimulated cGMP generation. cGMP production by mesenteric arteries was stimulated by sodium nitroprusside but not by ANF or CNP. Autoradiographic localization of I-125-ANF and I-125-ET-1 showed that in the case of ANF, most specific binding occurred in adipocytes, whereas for ET-1, specific binding was present in both adipose tissue and mesenteric arteries. Cross-linking of I-125-ANF followed by SDS-PAGE revealed two receptor species of 130 and 70 kD in adipose membranes and none in vascular tissue. Both were completely displaced by ANF, CNP, and C-ANF. I-125-[Sar(1),Ile(8)]Ang II binding assays in adipose tissue exhibited a single class of binding sites (B-max, 211 +/- 4 fmol/mg protein; K-d, 520 +/- 10 pmol/L). In mesenteric arteries, I-125-[Sar(1),Ile(8)]Ang II saturation assays showed little specific binding. The profile of ligands competing for I-125-[Sar(1),Ile(8)]Ang II was consistent with an AT(1) receptor subtype. I-125-ET-1 binding assays demonstrated high-affinity binding sites in both mesenteric arteries and adipose tissue (B-max, 179 +/- 21 and 312 +/- 7 fmol/mg protein, respectively; K-d, 215 +/- 45 and 180 +/- 111 pmol/L, respectively), the majority corresponding to BQ-123-sensitive sites. Thus, ANF and Ang II binding sites were either absent or barely expressed in the mesenteric artery. Binding sites for ET-1 were abundantly expressed in the mesenteric artery. Adipose tissue expressed high-affinity binding sites for ANF, Ang II. and ET-1, but their biological role, if any, remains to be defined.