Effect of Low-Dose Aspirin on Platelet Angiotensin II Binding and on the Pressor Response To

Abstract

Objective: To determine the effect of low-dose aspirin (75 mg o.d.) on platelet angiotensin II (AH) binding and on AH pressor sensitivity, and to study both the mechanism of the aspirin-induced reduction in AH pressor sensitivity and the potential use of platelet All binding in assessing the response to low-dose aspirin therapy.

Methods: Parallel studies of the effects of low-dose aspirin on platelet All binding and All pressor sensitivity were performed on 10 nonpregnant subjects. All infusions and platelet All binding estimations were performed prior to aspirin ingestion, 1 h after aspirin ingestion and after 1 month of oral aspirin ingestion.

Results: Platelet All binding was diminished 1 h after aspirin ingestion as compared to the initial values (P = 0.01). An increased AH infusion rate was required to produce a 10 mm Hg rise in systolic blood pressure (P < 0.05), and there was a decrease in the slope of the curve of systolic pressor responses to All (P = 0.01). After 1 month of aspirin, although the infusion parameters remained altered as compared to the initial values, binding approximated that prior to aspirin. The change in binding after 1 month of aspirin correlated with that of slope of the curve of systolic pressor responses to AH (P = 0.01).

Conclusions: The aspirin-induced reduction in All sensitivity may initially be partially mediated by decreased receptor density, possibly secondary to altered membrane fluidity. Reduced All sensitivity after 1 month of low-dose aspirin is likely to result from the alterations in prostaglandin ratios previously reported. The use of platelet All binding in assessing the response to aspirin therapy remains unproven.

Key Words:

• Angiotensin II
• Aspirin
• Blood pressure
• Platelet membrane glycoproteins
• Prostaglandins
• Receptors