Classification of angiotensin receptors in rat isolated uterus, portal vein, and aorta using a slowly dissociating antagonist [Sar1,Ile8]ANG II for receptor blockade.

Receptor blockade with the slowly dissociating angiotensin (ANG) antagonist, [Sar1,Ile8]ANG II, was used to determine dissociation constants (Kd) for angiotensins II and III at receptors in rat isolated uterus, portal vein and aorta. The Kd values obtained were 1) ANG II: uterus, 2.2 +/- 1.2 X 10(-8)M; portal vein, 8.5 +/- 2.5 X 10(-9)M; aorta, 7.8 +/- 1.7 X 10(-9)M; and 2) ANG III: uterus, 5.7 +/- 1.7 X 10(-7)M; portal vein, 4.5 +/- 3.1 X 10(-7)M; aorta, 1.4 +/- 0.5 X 10(-7)M. For either ANG II or ANG III, there were no clearly significant differences in the Kd values obtained for the smooth muscle tissues investigated. The derived Kd values provided a relationship between receptor occupancy and response that illustrated that the two peptides had similar efficacies in all three tissues. The method provides a quantitative description of receptors and suggests that the angiotensin receptor is of the same type in all three tissues.