Attenuation of sympathetic vasoconstriction by nifedipine: the role of vascular alpha 2-adrenoceptors.

The effects of nifedipine on hindlimb vasoconstriction caused by norepinephrine infusion and sympathetic stimulation (0.1-1.0 Hz) were compared in dogs given 0.12 mg/kg prazosin or 0.3 mg/kg rauwolscine. Constrictions due to stimulation or norephinephrine with prazosin, presumed to be mediated by vascular alpha 2-adrenoceptors, were significantly attenuated by 30 micrograms/kg nifedipine, while constrictions with rauwolscine, presumably alpha 1-mediated, remained unaffected. These data support the hypothesis that the antihypertensive effect of calcium antagonists is based upon interference with alpha 2-mediated sympathetic vasoconstriction.