PHOTOAFFINITY-LABELING OF THE RAT ISOLATED PORTAL-VEIN - DETERMINATION OF AFFINITY CONSTANTS AND SPARE RECEPTORS FOR ANGIOTENSIN-II AND ANGIOTENSIN-III

  • 1 January 1984
    • journal article
    • research article
    • Vol. 231  (1) , 137-140
Abstract
Photoaffinity labeling of the isolated rat portal vein with [azidobenzoic acid1, isoleucine8]angiotensin II resulted in selective partial inactivation of angiotensin receptors without affecting norepinephrine receptors. Establishment of dose-response curves to angiotensin II and III before and after photoaffinity labeling has permitted the calculation of spare receptors and affinity constants for angiotensins II and III. Spare receptors appear to exist for angiotensin II (> 60%) but not for angiotensin III. Evidently, angiotensin III has a higher binding affinity (K = 6 .times. 10-8 M) than angiotensin II (K = 3 .times. 10-7 M) but is considerably less potent than angiotensin II in eliciting the contractile response. If angiotensins II and III act at the same receptors in the portal vein, angiotensin III could inhibit the constricting action of angiotensin II and thereby play a role in the angiotensin-mediated control of portal venous capacity.