Effects of erythromycin on contractility of isolated myometrium from pregnant rats

OBJECTIVE: Erythromycin is a stimulant of motor activity in the stomach, but its effects on the uterus have not been studied and only its antibiotic properties have been considered in the treatment of idiopathic preterm labor. The objective of this study was to characterize in vitro the effect of erythromycin on the contractility of the pregnant rat uterus. STUDY DESIGN: Myometrial strips from pregnant rats were suspended 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 in phasic contractions induced by oxytocin or carbachol. This effect started at 0.01 mmol/L. At 1 mmol/L erythromycin reduced the contractions amplitude to 22% of the control and the frequency was reduced to 38% of control. CONCLUSION: We conclude that erythromycin produces a decrease in the pregnant rat myometrial activity in vitro, independent of the stimulant.