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 of 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 tension recording. Responses to cumulative concentrations of fluoxetine, imipramine, nortriptyline, and serotonin in the absence and presence of the monoamine reuptake inhibitors were studied. Results: Neither of the monoamine reuptake inhibitors significantly influenced spontaneous contractile activity, whereas the concentration-dependent increase in activity induced by serotonin was inhibited in rings from both midterm and term pregnant rats. Conclusions: The reported increase in preterm delivery in women receiving fluoxetine during the third trimester cannot be explained by a direct effect on uterine contractility. (Am J Obstet Gynecol 2000;182:296-9.)