Different sensitivities of rabbit isolated blood vessels exhibiting co-transmission to the slow calcium channel blocker, nifedipine.

1. Antagonist drugs were used to separate the purinergic and adrenergic contributions as well as the adrenoceptor sub-types involved in the sympathetic vasoconstrictor responses produced by electrical field stimulation in rabbit isolated ileocolic and proximal saphenous arteries. Blocking drugs were applied either alone or in various combinations and sequences. 2. Nifedipine attenuated vasoconstrictor responses to sympathetic nerve stimulation both in the presence and in the absence of alpha-adrenoceptor blocking agents. However in the presence of alpha,beta-methylene ATP, nifedipine produces at best only a small attenuation of the vasoconstrictor response. 3. These results suggest that the purinergic component of the response to sympathetic nerve stimulation, at least in these tissues, can be antagonized by nifedipine, whereas the alpha 1-adrenoceptor-mediated response is relatively resistant.