Prejunctional actions of some beta-adrenoreceptor antagonists in the vas deferens preparation of the guinea-pig.

1. The beta-adrenoceptor antagonists propranolol, pronethalol, MJ 1999 and Ciba 39089-Ba reduced responses to field stimulation of the guinea-pig isolated vas deferens preparation without significantly affecting responses to exogenously added noradrenaline.2. This prejunctional blocking action of the drugs cannot be correlated with their action as beta-adrenoceptor antagonists or non-specific depressants.3. The blockade produced was more pronounced at low (5-20 Hz) than at high (50 Hz) frequencies of stimulation.4. The blockade was slow in onset, and once established was poorly reversed by washing the preparation over a period of 1 to 2 h.5. The blockade produced could be reversed by dexamphetamine and cocaine.6. These experiments suggest that the beta-adrenoceptor antagonists may have some actions which closely resemble those of the adrenergic neurone blocking agent guanethidine.