Adrenergic contribution to the motor transmission in the dog vas deferens.

Isolated vas deferens preparations from 9 dogs were subjected to electrical stimulation and chemical excitation under physiological conditions. The experimental smooth muscle cylinders were confined to the terminal 3 cm portions of either the distal 'urethral' segment or the proximal 'epididymal' segment. Intermittent field stimulation, at 60 sec intervals, was provided by a stimulator of low output impedance under constant parameters of frequency and voltage and an occasionally varied pulse width. Results from this examination completely confirmed the following: (i) a high degree of contractile sensitivity to minute doses of noradrenaline (0.03--0.03 micron; 10(-8)-10(-7) g/ml) and tyramine 0.58 micron (10(-7) g/ml; (ii) an apparent ease and rapidity of extinguishing the electrically-induced twitches by either small doses of phentolamine 0.25 micron (10(-7) g/ml) or phenoxybenzamine 5.8 micron (2 x 10(-6) g/ml); (iii) a complete absence of any inhibitory action by tyramine or noradrenaline on the electrically-induced twitches. The behavior of this motor transmission of the longitudinal muscle of the vas deferens to classical alpha-adrenoceptor blocking agents and the intense susceptibility to the motor actions of the putative neurotransmitter clearly fit in with a picture of an adrenergic implication in this mode of transmission.