Comparative effects of nitrendipine and verapamil on neuroeffector transmission in the rabbit ear artery

The purpose of the present study was to evaluate and compare the effects of the calcium antagonists nitrendipine and verapamil on nerve-evoked constrictions and on norepinephrine (NE) release in the isolated, perfused rabbit ear artery. The response of the ear artery to nerve stimulation consists of an early phasic constriction (P response) and a late, slow-developing tonic constriction (T response). Both calcium antagonists were much more potent in causing inhibition of the T than P responses. For nitrendipine the EC50 (6.6 +/- 2.3 X 10(-8)M) for inhibition of T response was 450 times lower than the EC50 for inhibition of P response. Verapamil exhibited less selectivity for T response: the EC50 for inhibition of T response was 17 times lower than the EC50 for inhibition of the P response. Nitrendipine (3.3 X 10(7) to 3.3 X 10(-5) M) did not alter the nerve-evoked release of [3H]NE from arteries preincubated with [3H]NE. Verapamil at 3.3 X 10(-6) and 3.3 X 10(-5)M enhanced both spontaneous and nerve-evoked [3H]NE release.