Atrial natriuretic peptide receptors in sheep cotyledons.

Effects dependent on atrial natriuretic peptide are mediated through specific atrial natriuretic peptide plasma membrane receptors. We previously demonstrated the presence of specific atrial natriuretic peptide receptors in human placental membranes. We asked whether atrial natriuretic peptide specific receptors are present in sheep cotyledons. Sheep cotyledons were obtained from pregnant ewes at 125 to 142 days' gestation. Each cotyledon was separated into two components, the outer layer (maternal capsule) and the spongy inner layer (fetal component). A microsomal plasma membrane fraction was prepared from each layer. Atrial natriuretic peptide receptors were detected by in vitro radioligand techniques with 125I-alpha-human atrial natriuretic peptide. In sheep cotyledons there are two sets of atrial natriuretic peptide receptors that show either high-affinity/low-capacity or low-affinity/high-capacity binding characteristics. Moreover, membranes from the inner layer (fetal component) appear to have a lower concentration of high-affinity atrial natriuretic peptide binding sites than those from the maternal capsule.