| Abstract: | Specific binding sites for angiotensin II (Ang II) were localized in the red pulp of the spleen of rats and mice by quantitative autoradiography using 125I-Sar1-Ang II as a ligand. In the rat, the binding was saturable and specific, and the rank order for Ang II derivatives as competitors of 125I-Sar1-Ang II binding correlates well with their affinity for Ang II receptors in other tissues. Kinetic analysis in the rat spleen revealed a single class of binding sites with a KD of 1.11 nM and a Bmax value of 81.6 fmol/mg protein. Ang II binding sites were also localized on isolated rat spleen cells with similar affinity but with much lower Bmax, 9.75 fmol/mg protein. Ang II receptors were not detected in thymus sections from rats or mice, or on isolated rat thymocytes. The binding sites described here might represent a functional Ang II receptor with a role in the regulation of splenic volume and blood flow and in the modulation of the lymphocyte function. |
