EFFECTS OF ERYTHROMYCIN ON CONTRACTILITY OF ISOLATED MYOMETRIUM FROM PREGNANT RATS

OBJECTIVE: Erythromycin is a stimulant of motor activity in the stomac h, but its effects on the uterus have not been studied and only its an tibiotic properties have been considered in the treatment of idiopathi c preterm labor. The objective of this study was to characterize in vi tro the effect of erythromycin on the contractility of the pregnant ra t uterus. STUDY DESIGN: Myometrial strips from pregnant rats were susp ended in tissue baths. Isometric contractions were monitored by force transducers in response to various agents that were added to the bath solution. RESULTS: Erythromycin exposure caused a sustained decrease i n phasic contractions induced by oxytocin or carbachol. This effect st arted at 0.01 mmol/L. At 1 mmol/L erythromycin reduced the contraction s amplitude to 22% of the control and the frequency was reduced to 38% of control. CONCLUSION: We conclude that erythromycin produces a decr ease in the pregnant rat myometrial activity in vitro, independent of the stimulant.