Treatment of Hypertension Induces a Fall in Platelet Basal Cytoplasmic Calcium Concentration without Influencing Platelet Aggregation

Abstract

SummaryThe relationship between blood pressure and platelet basal cytoplasmic calcium concentration ([Ca2+]i) and platelet sensitivity to aggregating agents in hypertension has been investigated in hypertensive patients and normotensive subjects. Ten severely hypertensive patients whose blood pressures were poorly controlled with metoprolol, were given calcium antagonist (either nifedipine or felodipine) as a second line agent. Venous blood samples were collected at each treatment phase for measurement, in whole blood, of platelet aggregation in response to ADP and collagen, and of basal [Ca2+]i using fura-2. Control of blood pressure by the combination of metroprolol and a calcium antagonist induced a significant decrease in median [Ca2+]i from 116 (76–181) to 73 (60–83) nM, which was similar to the median value of 70 (61–80) nM obtained in 14 normotensive subjects. Overall [Ca2+]i correlated with mean blood pressure (r = 0.51). Treatment of hypertension with calcium antagonist did not change the response of platelets to collagen or ADP. The results confirm that effective treatment of hypertension significantly reduced basal [Ca2+]i in platelets but raise doubts whether elevated basal [Ca2+]i is necessarily the sole mechanism by which the sensitivity of platelets to aggregatory agents is increased in hypertension.

Platelet Hyperactivity in Hypertensive Older Patients Is Controlled by Lowering Blood Pressure

“…Moreover, Shindler et al 27 had demonstrated that captopril, but not many other ACE inhibitors, affected the in vitro production of some cytokines in blood mononuclear cells, suggesting that the effect was not specifically related to the inhibition of the angiotensin‐converting enzyme. Similarly, as for nifedipine, although the role of Ca 2+ ‐antagonists on platelet function has been a matter of debate for many years, recent works have demonstrated that nifedipine, at therapeutic, antihypertensive doses does not affect platelet activity 28 , 29 . This datum has been confirmed in our work: in the four patients who did not respond to the combined antihypertensive treatment with quinapril plus nifedipine, no modification of platelet function parameters was observed compared with baseline levels.…”