Methyldopa abolishes neurally evoked contractions of the vas deferens in vitro.

Low concentrations of methyldopa (2 microgram/ml - 20 microgram/ml) reduced neurally evoked contractions of the isolated guinea-pig and the rat vas deferens. These contractions were completely abolished when the vas was incubated with methyldopa (200 microgram/ml - 400 microgram/ml) for 1.5 hr +/- 0.1 hr (guinea-pigs) and 3.0 hr +/- 0.5 hr (rats). Vasa deferentia incubated with methyldopa became supersensitive to noradrenaline and dopamine. Vas deferentia from reserpinized animals showed reduced contractions upon electrical stimulation but became supersensitive to dopamine and noradrenaline. Reserpine pretreatment diminished the response of the vas to tyramine; however, methyldopa restored the responses to a greater magnitude suggesting the formation of methyldopamine and methylnoradrenaline. The possible mechanisms of action of methyldopa is discussed.