Localization of atrial natriuretic peptide, ANP-(99-126) binding sites in the rat thymus and spleen with quantitative autoradiography.

Binding sites for atrial natriuretic peptide, ANP-(99-126) were studied in lymphoid organs of the rat with quantitative autoradiography. Tissue sections were incubated in the presence of 0.13 nM 125I-ANP-(99-126) followed by autoradiography using [3H]-Ultrofilm, and the results were analyzed by computerized densitometry and comparison to 125I-standards. Specific ANP binding sites were localized in the medulla and the cortex of the rat thymus and in the white pulp of the rat spleen, with apparent binding sites concentrations of 93, 65, and 126 fmol/mg protein, respectively. The presence of ANP binding sites in areas related to the maturation and function of lymphocytes, and to the production of thymic hormones, suggests the possibility of a role of circulating ANP in the modulation of the immune response.