Pharmacological stroke prevention: Short- and long-term cerebrovascular effects of dihydropyridine calcium antagonists in hypertensive patients

The aim of our studies was to evaluate the effect on blood pressure (BP) and cerebral blood flow (CBF) of acute treatment in hypertensive emergencies and of chronic and acute treatment in uncomplicated hypertensives with calcium antagonists. Ten patients with high blood pressure requiring emergency reduction were randomized to treatment with oral nifedipine or intravenous clonidine. The effect on CBF was investigated using xenon 133. Twenty-one patients with mild to moderate hypertension were randomly assigned to nitrendipine (n = 10) or to verapamil treatment for 4 weeks. After 14 days wash-out all patients received chlorthalidone for 4 weeks. CBF was measured before calcium antagonists, after 4 weeks, after wash-out and after 4 weeks chlorthalidone. Five patients with mild to moderate hypertension entered in an ongoing study. After 14 days placebo CBF and BP reduction were measured 2 h and 6 weeks after nitrendipine. In hypertensive emergencies nifedipine and clonidine lowered BP significantly, whereas CBF increased after nifedipine and decreased after clonidine. After chronic treatment with nitrendipine and verapamil and after chlorthalidone the BP-lowering effect was significant, whereas CBF remained unchanged. Two hours after nitrendipine BP decreased and CBF remained unchanged. The reason for increasing CBF in hypertensive emergencies after nifedipine is the spasmolytic effect on cerebral vessels. The unchanged CBF after short- and long-term treatment with nitrendipine is due to the fact that in these patients the autoregulatory mechanism is intact.