The effect of verapamil, diltiazem and nifedipine on baroreceptor reflexes.

Heart rate in nifedipine treated patients tends to be higher than in those treated with verapamil or diltiazem. This may be due, among other causes, to a differential action on cardiac baroreflexes. As conclusions of previous studies were controversial, we decided to study the effect of verapamil, diltiazem and nifedipine on baroreflex sensitivity. After 3-5 week treatment, heart rate response to various doses of i.v. phenylephrine and sodium nitroprusside was recorded in conscious rats. The slope of the regression line relating change of heart rate to change in blood pressure, was depressed in verapamil treated rats compared to that in control, diltiazem or nifedipine treated rats (p less than 0.0001). The role of the autonomic nervous system in modulation of baroreflexes was investigated by pretreatment of the animals with propranolol or atropine. The results were compatible with the hypothesis that verapamil depresses adrenergic nerve activity and this may contribute to decreased, vasodilation-induced baroreceptor reflexes.