Nifedipine and alpha adrenoceptor antagonism.

The effects of nifedipine and placebo on the pressor responses to methoxamine, alpha-methylnorepinephrine, and angiotensin II were compared in normal subjects. Nifedipine shifted the pressor dose-response curves of all three agonists to the right. The dose ratios of the three agonists were of the same order. Thus in contrast to the findings in animals, nifedipine is not a selective alpha 2-adrenergic antagonist in man, although it may lower blood pressure partly by antagonism of norepinephrine and angiotensin II.