Effects of nicardipine and diltiazem on alpha-adrenoceptor responses in canine saphenous veins.

The effects of calcium antagonists, diltiazem and nicardipine (-6.0 to -4.0 log mol/l), on the contractile responses to noradrenaline, methoxamine and BHT-920 in isolated canine saphenous vein rings, were studied with isometric tension recordings. Concentration-effect curves to the alpha-agonists were obtained in the control state and in the presence of diltiazem or nicardipine. Propranolol (-6.0 log mol/l) was present in the bath throughout. Diltiazem had no significant inhibitory effect on the responses mediated by all three agonists. Nicardipine (-5.0 and -4.0 log mol/l) produced a small but significant inhibitory effect on the responses to noradrenaline and methoxamine while it had no effect on the response to BHT-920. The effects of nicardipine were greatest on the responses to methoxamine. These calcium antagonists appeared to have only small post-synaptic inhibitory effects on the contractile responses to alpha-agonists in the canine saphenous vein with nicardipine exerting a greater inhibitory influence than diltiazem.