The interference by nicardipine and diltiazem on α‐adrenergic receptor–mediated vasoconstriction in isolated human subcutaneous arterioles

The effects of nicardipine and diltiazem on α‐adrenergic receptor–mediated vasoconstriction in isolated human subcutaneous arterioles was studied. Arterioles were mounted in a myograph and stimulated at 50% of maximal contraction with norepinephrine. The vasoconstrictor responses to an unrelated agonist, endothelin, was used for comparison. The percentage of decrement in tension produced by nicardipine or diltiazem was the parameter evaluated. Both calcium channel blockers caused an equipotent and dose‐dependent relaxation of the vasoconstrictor responses to norepinephrine and endothelin I. The equipotent α‐adrenolytic effect exerted by nicardipine and diltiazem in subcutaneous arterioles contrasts with the preferential antagonism by local nicardipine in the forearm. This suggests that the interaction between α‐adrenergic receptor activation and structurally unrelated calcium channel blockers is affected by the regional and functional characteristics of the vessels under study. Clinical Pharmacology and Therapeutics (1993) 54, 70–75; doi: 10.1038/clpt.1993.113