Objective: The aim of this study was to investigate the effects of melatonin, a hormone, on oxytocin-induced contractility of isolated myometrium.

Materials and method: Myometrial strips were removed from a total of 25 non-pregnant Wistar female rats (weighing 200-250 g), which were confirmed to have regular sexual cycle by vaginal smear technique. Animals in oestrus cycle were sacrificed by decapitation and isolated uterus placed in a petri dish containing the Krebs solution. About 1X0.2X0.1 cm myometrium strips were isolated and placed in an organ bath containing Krebs solution at 37 degrees C and pH 7.4, constantly bubbled with 95% oxygen - 5% carbon dioxide. Isometric contractions were recorded under 1 gram of resting tension. After a 30-120 minutes equilibration period myometrial strips were stimulated with oxytocin and the effects of different doses of melatonin (1mM, 3mM, 5mM) were applied.

Results: Oxytocin-induced contractions of myometrium were accepted as control. 1mM dose of melatonin hormone reduced these contractions particularly, whereas administration of 3mM melatonin showed a moderate inhibitor effect. However, administration of 5mM dose of melatonin was seen to completely inhibit the oxytocin-induced myometrial contractions.

Conclusion: It was determined that melatonin had an inhibitory effect on the contractions of myometrium.