Summary
The 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.
