Atrial natriuretic peptide receptors in sheep cotyledons

Atrial natriuretic factor in hydrops fetalis caused by Rh isoimmunisation

Plasma concentrations of atrial natriuretic factor were determined by radioimmunoassay in 16 human fetuses of between 19 and 38 weeks' gestation. Fifteen fetuses had varying degrees of anaemia as a result of Rh isoimmunisation, and one fetus was normal. Eight fetuses had ultrasonographic evidence of severe hydrops fetalis and an additional three fetuses had mild hydrops. Severely hydropic fetuses were more anaemic and immature than those with mild or no hydrops. Among fetuses from which samples were taken before in utero transfusion, concentrations of atrial natriuretic factor were higher in those with severe hydrops than in the other groups. An inverse relationship between the haemoglobin concentration and that of atrial natriuretic factor was found. In four fetuses in which severe hydrops resolved after intravascular transfusions in utero, there were significant decreases in plasma atrial natriuretic factor concentrations; in the fifth fetus the decrease was less pronounced. Raised concentrations of atrial natriuretic factor in fetuses with severe anaemia and hydrops may be the result of atrial natriuretic factor release induced by hypoxia.

Atrial natriuretic peptide receptors in guinea pig placentas

The multiple physiologic effects of atrial natriuretic peptide are mediated through specific atrial natriuretic peptide plasma membrane receptors. We have attempted to determine whether atrial natriuretic peptide receptors are present in guinea pig placentas and subplacentas at approximately 45 and 65 days' gestation. A microsomal plasma fraction was prepared from each component. Atrial natriuretic peptide receptors were detected by in vitro radioligand techniques with alpha-human atrial natriuretic peptide labeled with iodine 125. In placentas we identified one set of specific binding sites for atrial natriuretic peptide at both gestational ages. Although the maximal concentration of the receptors did not change with advancing gestation, the dissociation constant was higher at 65 than at 45 days' gestation. In subplacentas two sets of binding sites were identified, one of low capacity-high affinity and the other of low affinity-high capacity. The maximal concentration of the atrial natriuretic peptide receptors did not change as a function of gestation. However, the dissociation constant, for both the high- and low-affinity sites, significantly decreased with advancing gestation.