α-Human atrial natriuretic polypeptide binding sites in human adrenal membrane fractions

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In a previous study evidence was presented that synthetic α-human atrial natriuretic polypeptide (α-hANP) significantly inhibits the secretion of aldosterone, cortisol, and dehydroepiandrosterone (DHEA) from cultured human adrenal cells. In the present work using crude membrane fractions prepared from human adrenal tissues obtained at autopsy, we noted the existence and molecular weight of specific binding sites for [ 125I]α-hANP. The mean maximal binding capacity ( B max) and dissociation constant ( K d) of 4 human adrenal membrane fractions were 8.0 ± 1.6 fmol/mg protein and 25.7 ± 7.4 pM, respectively, as calculated by Scatchard plot analysis. The interaction of [ 125I]α-hANP with the high-affinity binding sites in human adrenal membrane fractions was unaffected by the addition of lysine vasopressin (LVP), somatostatin-14 and angiotensin-II (A-II). When the membrane fractions were incubated with [ 125I]α-hANP and then cross-linked with disuccinimidyl suberate (5 mM), the 67,000-Da protein was specifically radiolabeled. The very high affinity of [ 125I]α-hANP binding sites suggests that human adrenal steroidogenesis may be influenced by plasma levels of hANP, under physiological conditions.