Abstract
Pharmacological characteristics of Musculus retractor phalli cranialis, a smooth muscle tissue isolated from cock, were examined. This muscle showed spontaneous rhythmic contractions in physiological salt solution. Electrical field stimulation inhibited the spontaneous contractions and relaxed the muscle. Effect of electrical stimulation was inhibited by tetrodotoxin but not by hexamethonium, propranolol, prazosin or atropine. Norepinephrine and isoproterenol also inhibited the spontaneous contraction and relaxed the muscle. In the presence of propranolol, however, norepinephrine induced a contraction which was inhibited by prazosin. Carbachol induced a contraction which was inhibited by atropine. Substance P also induced a contraction. High concentration of K+ (120 mM) induced a contraction which was augmented by propranolol. ATP and neurotensin were ineffective. These results indicate that the M. Retractor phalli crsnialis is a spontaneously active smooth muscle and is controlled mainly by non-adrenergic, non-cholinergic inhibitory neurons.
