The Effect of Some Substances on the Isolated Bull Retractor Penis Muscle

The effect of catechol amines, other biogenic amines and polypeptides, acetylcholine and other choline esters, nicotine, and various autonomic blocking agents on strips of the bull retractor penis suspended in Tyrode solution was studied. The strips were vigorously contracted by low concentrations of adrenaline and noradrenaline but they were most insensitive to acetylcholine and other choline esters. The catechol amine‐induced contractions were inhibited by low con centrations of phenoxybenzamine. The relaxations produced by isoprenaline were inhibited by pronethalol. It is suggested that the tonic contraction of the muscle is maintained by a continuous discharge of adrenergic nerve impulses. The hypothesis is presented that relaxation occurs at interruption of the adrenergic activity by impulses conducted mainly along the pelvic nerves. The pelvic nerves probably form cholinergic ganglionic or postganglionic inhibitory synapses with the adrenergic nerves concerned, The peripheral autonomic mechanism of penile erection is discussed on the presumption that the muscles of the penile artery are subjected to a similar nervous control as the retractor penis. It is assumed that there are no differences in principle between bulls and dogs with respect to the nervous mechanisms in question.