Characterization of angiotensin II receptor subtypes in the rat spleen

Quantitative autoradiography was used to determine the subtype of ANG receptors in the red pulp of the rat spleen. The AT1 antagonist DuP 753 competed for ANG binding with high affinity; binding was abolished by dithiothreitol. The AT2 competitor CGP 42112 A showed lower affinity, and the AT2 competitor PD 123177 did not affect binding at 10(-5) M. These data indicated the presence of only AT1 receptors. AT1 receptor number was similar in immature (2 weeks old) and adult (8 weeks old) rats. Binding was sensitive to guanine nucleotides, suggesting an association with G-proteins. Angiotensin II, at a dose of 10(-7) M, stimulated inositol phosphate formation 33% over control values in spleen from 8-week-old rats. This effect was significantly blocked by 10(-5) M DuP 753. We suggest a possible role of AT1 receptors in the regulation of splenic volume, blood flow, and lymphocyte function.