Evidence for adrenergic transmission in the circular smooth muscle of the guinea-pig seminal vesicle.

Spontaneous contractile activity of the circular smooth muscle of the guinea-pig seminal vesicle consists of twitch-like contractions with a mean frequency of 2.7/min. The amplitude of responses to repetitive stimulation depended on the frequency of stimulation at constant pulse duration and on the pulse durations at constant frequency of stimulation. Mechanical summation in the tension development was observed at low frequency of repetitive stimulation. Adrenaline, noradrenaline and phenylephrine increased the frequency and amplitude of spontaneous contractions. The excitatory actions of adrenaline and noradrenaline were antagonized by phentolamine and phenoxybenzamine. DOPA, metanephrine and normetanephrine were not effective. Tyramine enhanced the spontaneous activity and its action was antagonized by phentolamine. Isoprenaline, at high concentrations, enhanced spontaneous activity, but in the presence of phentolamine, the spontaneous activity was inhibited by isoprenaline and orciprenaline. Isoprenaline inhibited the enhanced spontaneous activity induced by adrenaline, noradrenaline and tyramine. Spontaneous contractions were potentiated by tetrodotoxin, procaine, guanethidine and dibenamine but were not affected by nicotine and phenoxybenzamine. Evoked responses to repetitive stimulation were blocked or suppressed by tetrodotoxin, yohimbine, nicotine, guanethidine and phentolamine. The evoked responses were partially inhibited by phenoxybenzamine. In contrast, evoked responses were enhanced by hexamethonium and dibenamine. These results provide further support for the conclusion that the innervation of the circular smooth muscle of the guinea pig seminal vesicle is mainly alpha-excitatory adrenergic.