EFFECT OF LOW-DOSE ASPIRIN ON PLATELET ANGIOTENSIN-II BINDING AND ON THE PRESSOR-RESPONSE TO INFUSED ANGIOTENSIN-II

Objective: To determine the effect of low-dose aspirin (75 mg o.d.) on platelet angiotensin II (AII) binding and on AII presser sensitivity, and to study both the mechanism of the aspirin-induced reduction in A II presser sensitivity and the potential use of platelet AII binding i n assessing the response to low-dose aspirin therapy. Methods: Paralle l studies of the effects of low-dose aspirin on platelet AII binding a nd AII presser sensitivity were performed on 10 nonpregnant subjects. AII infusions and platelet AII binding estimations were performed prio r to aspirin ingestion, 1 h after aspirin ingestion and after 1 month of oral aspirin ingestion. Results: Platelet AII binding was diminishe d 1 h after aspirin ingestion as compared to the initial values (P = 0 .01). An increased AII infusion rate was required to produce a 10 mm H g rise in systolic blood pressure (P < 0.05), and there was a decrease in the slope of the curve of systolic presser responses to AII (P = 0 .01). After 1 month of aspirin, although the infusion parameters remai ned altered as compared to the initial values, binding approximated th at prior to aspirin. The change in binding after 1 month of aspirin co rrelated with that of slope of the curve of systolic presser responses to AII (P = 0.01). Conclusions: The aspirin-induced reduction in AII sensitivity may initially be partially mediated by decreased receptor density, possibly secondary to altered membrane fluidity. Reduced AII sensitivity after 1 month of low-dose aspirin is likely to result from the alterations in prostaglandin ratios previously reported. The use of platelet AII binding in assessing the response to aspirin therapy r emains unproven.