The isolated circular muscle layer of the vas deferens of the guinea-pig.

1 A method is described for the removal of the outer longitudinal layer of muscle from the guinea-pig isolated vas deferens. The remaining tube of circular muscle was perfused at constant flow for recording changes in pressure in response to transmural electrical stimulation or to drugs. 2 The response to transmural stimulation was a rise in perfusion pressure at frequencies of stimulation of 5 to 50 Hz for trains of 16 to 256 pulses. At some frequencies and train lengths a second rise in pressure (the after-response) occurred after the cessation of the stimulus train. 3 Perfused vasa stripped of their longitudinal muscle did not develop longitudinal tension on electrical stimulation nor on intraluminal or extraluminal exposure to agonists. 4 Stripped perfused vasa gave concentration-dependent pressure rises to noradrenaline but not to acetylcholine. 5 Responses to transmural stimulation and to noradrenaline were antagonized by thymoxamine. Cocaine or desmethylimipramine increased the duration of the after-response to transmural stimulation. Reserpine pretreatment almost abolished the response and after-response. The after-response, but not the response, was increased by physostigmine and antagonized by atropine. 6 The results are discussed in relation to the known histochemical and electronmicroscopical demonstrations of dense noradrenergic and cholinergic populations of nerve terminals in the circular layer. It is suggested that mechanisms may exist for the separate control of the longitudinal and circular layers as a basis for propulsive activity.