Transmission to the longitudinal muscle of the guinea-pig vas deferens: The effect of pretreatment with guanethidine.

1 Tissue was taken from guinea-pigs that had been injected with guanethidine (100 mg/kg, i.p.) 24 h before they were killed, and from paired control animals.2 Pretreatment with guanethidine caused a significant, substantial, and sometimes complete reduction of the nerve-mediated contractions of the vas deferens. There were no significant changes in the responses of the ileum to stimulation of cholinergic nerves or of the distal colon to stimulation of intrinsic (non-adrenergic) inhibitory nerves. Responses of the vas deferens and ileum to acetylcholine were unchanged, but contractions of the vas deferens elicited by exogenous noradrenaline were enhanced.3 The nerve-mediated contractions of the vas deferens were restored by exposing it to (+)-amphetamine followed by noradrenaline in vitro.4 It is concluded that noradrenaline is the transmitter released from motor nerves to the longitudinal muscle of the guinea-pig vas deferens. Possible explanations for the ineffectiveness of receptor blocking agents in antagonizing transmission are discussed.