Intimacy of the neuroeffector junction and resistance to α‐adrenoceptor‐blockade of the neurogenic contractile response in vasa deferentia from guinea pig and rat

The effect of phentolamine on the neurogenic contractile response in vasa deferentia from rat and guinea pig was studied during Wallerian degeneration. This response was also investigated after partial denervation (surgery or chemical sympathectomy by guanethidine treatment) in vasa deferentia from guinea pig. During Wallerian degeneration the response showed a gradual increase in sensitivity to phentolamine and was abolished in the late stages. The neurogenic contractile response of the partially denervated vas deferens was blocked by low concentrations of phentolamine. It is concluded that decreased intimacy of the neuroeffector junctions leads to increased susceptibility to alpha-adrenoceptor blockade of the contractile response to nerve stimulation. It is further concluded that the motor transmission in the vas deferens is essentially adrenergic. The resistance to alpha-adrenoceptor blockade of the initial phase of the contractile response to nerve stimulation of intact vasa deferentia from guinea pig and rat might well be explained by the "proximity theory" of Dale & Gaddum although participation of supplementary mediators cannot be excluded.