Effect of fluoxetine on contractile activity of pregnant rat uterine rings

OBJECTIVE: We sought to compare the effects of fluoxetine, imipramine, and nortriptyline on spontaneous and serotonin-activated contractile activity o f the uterine rings from midterm and term pregnant rats. STUDY DESIGN: Uterine rings from timed-pregnant Sprague-Dawley rats on day 14 (midgestation) and day 22 (term gestation) were used for isometric tensi on recording. Responses to cumulative concentrations of fluoxetine, imipram ine, nortriptyline, and serotonin in the absence and presence of the monoam ine reuptake inhibitors were studied. RESULTS: Neither of the monoamine reuptake inhibitors significantly influen ced spontaneous contractile activity, whereas the concentration-dependent i ncrease in activity induced by serotonin was inhibited in rings from both m idterm and term pregnant rats. CONCLUSIONS: The reported increase in preterm delivery in women receiving f luoxetine during the third trimester cannot be explained by a direct effect on uterine contractility.