Relaxant effect of benzodiazepines on uterine rings isolated from estrogen-treated rats

K(+)-contracted rat uterine rings were relaxed in a concentration-dependent manner by the benzodiazepines Ro 5-4864, diazepam and clonazepam, as well as by the putative peripheral benzodiazepine antagonist PK 11195. The relaxation induced by diazepam was not counteracted by the central antagonist Ro 15-1788 (10 microM), and the relaxant effects of Ro 5-4864 and of diazepam were not prevented by either the GABAA antagonist bicuculline (10 microM) or the beta-adrenoceptor antagonist propranolol (1 microM). The mechanism underlying the relaxant effects of benzodiazepines on K(+)-contracted uterine rings is still under study.