Suppression of the excitatory adrenergic neurotransmission; a possible role of cholinergic nerves in the retractor penis muscle.

The excitatory adrenergic response to transmural nerve stimulation of the isolated retractor penis (rp) of dog, cat, horse, boar, elk, bull, ram and goat, as well as the evoked release of 3H from dog rp preloaded with 3H-noradrenaline were studied. In untreated preparations a low concentration of scopolamine could markedly increase the excitatory adrenergic response. On the contrary, physostigmine per se suppressed this response and so did acetylcholine. Scopolamine or atropine totally prevented these suppressions. They also immediately restored the suppressed responses in spite of continuous presence of physostigmine and/or acetylcholine. In the rat rp there was no suppression of the response by physostigmine. Physostigmine decreased the evoked release of 3H and this effect was counteracted by scopolamine. The rp of dog, gelding, boar, hog, bull and ram contained considerable amounts of noradrenaline and also of acetylcholine. It is suggested that one action of cholinergic nerves in the rp is muscarine suppression of the excitatory adrenergic neurotransmission.