SYMPATHETIC NERVE-FREE VASCULAR MUSCLE

¹ Departments of Pharmacology and Pathology, UCLA School of Medicine, Los Angeles, California

A nerve-free rabbit aortic strip has been prepared by selective mechanical destruction of the sympathetic nerve-containing layers of the vessels, namely the adventitia and adventitio-medial junction. After denervation, the preparation becomes unresponsive to transmural electrical stimulation and to small doses of tyramine and nicotine. The mean response of the nerve-free strips to a maximum dose of l-norepinephrine was 65% of the control. Denervation had no effect on the characteristics of response of the strip to l-norepinephrine (median effective dose and slope of probit response-log dose curve). This is consistent with the low density and limited distribution of the sympathetic effector plexus in elastic arteries. Cocaine (3 µg/ml) increased significantly (P = .01-.02) the sensitivity of the normal strip to l-norepinephrine in comparison to that of the nerve-free strip and, in addition, increased the maximum response of both strips to l-norepinephrine. The sensitivity of the nerve-free strips and the slopes of the dose-response curves of both strips to l-norepinephrine was unaltered by cocaine. It is concluded that the increased response of aortic strips to l-norepinephrine after cocaine is due to a presynaptic action and also to a direct action on the vascular muscle cells.

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