The effects of benzoylecgonine, oxytocin, ritodrine and atosiban on the contractility of myometrium. An experimental study.

To investigate the response of pregnant and non pregnant rat myometrium to benzoylecgonine, a cocaine metabolite, and oxytocin and to investigate the efficiency of ritodrine and atosiban to overcome the effects of benzoylecgonine and oxytocin. Isolation of rat myometrial tissue and recording of contractile activity with isotonic muscle transducer. Benzoylecgonine and oxytocin increase myometrial contractility, while atosiban and ritodrine induce myometrial relaxation. Atosiban was able to revoke the action of oxytocin but not the action of benzoylecgonine. Ritodrine was able to induce muscle relaxation in both oxytocin and benzoylecgonine administration. Cocaine metabolites seem to act on the myometrium through different pathways compared with oxytocin. After comparing two widely used tocolytic agents: atosiban and ritodrine, it is indicated that only ritodrine, a beta2 adrenergic receptor agonist, can inhibit the action of cocaine metabolites. This finding indicates that the actions of cocaine on adrenergic mechanisms are responsible to a large part for its effects on myometrium contractility. The use of beta2 adrenergic receptor agonists seems to be preferable for the treatment of myometrial contractions induced by cocaine consumption.