Fluoxetine causes decrease in intestinal motility

Background: Major depression is the most frequent disorder occurring in 16% of the population worldwide. In the middle of the 20 th  century, the discovery of selective serotonin (5-HT) reuptake inhibitors acted as a miracle in the antidepressant therapy. We explored the acute effects of fluoxetine and possible mechanism underlying the contractile effects of fluoxetine on isolated ileal smooth muscles of rabbit in vitro . Methods: Effects of increasing concentrations of acetylcholine (Ach), 5-HT and fluoxetine were studied on isolated ileal tissue of the rabbit in vitro by constructing cumulative concentration response curves. The ileal smooth muscle contractions were recorded on power lab (USA). Results: Ach, 5-HT and fluoxetine, produced a concentration-dependent reversible contraction of isolated ileal muscle of rabbit. The mean ± standard error of the mean of maximum amplitudes of contraction with Ach, 5-HT and fluoxetine, were 24.8±1.22 mm, 44±0.527 mm and 2.6±1.16 mm, respectively. Fluoxetine shifted the concentration-response curve right and downwards. Conclusion: Our study has indicated that fluoxetine on isolated ileal intestinal smooth muscle decrease the motility and this decrease in motility is possibly due to the inability of fluoxetine in vitro to enhance the serotonergic transmission and also because of the interaction of these agents with some of the other receptors, present in the intestinal smooth muscles.