The tocolytic effect of the butanol fraction of the glycoside extract of the fruits of Piper guineense
, was pharmacologically screened by measuring the uterine contractility. A state of oestrous was induced in three female rats through intramuscular injection of 0.1 µg per 100 g body weight of stilboestrol. The animals were sacrificed; the two horns of the uterus were carefully dissected free of fat and connective tissues and divided into two pieces. Dose response curves were obtained using oxytocin alone, oxytocin plus butanolic fraction of the glycoside extract, and oxytocin plus salbutamol. Pretreatment of the uterine tissues with the glycoside extract or salbutamol resulted in inhibition of uterine contraction at low concentrations of oxytocin. The dose response curve of oxytocin inhibition by the glycoside extract is similar to that of salbutamol. This suggests that the bioactive component of the extract could be a competitive antagonist of oxytocin action.