Effects of melatonin hormone on myometrium contractions

2. ABSTRACT The aim of this study was to investigate the effects of melatonin, a hormone, on oxytocin-induced contractility of myometrium isolated from female rats. Myometrial strips were removed from a total of 30 non-pregnant Wistar 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 minute equilibration period myometrial strips were stimulated with oxytocin and the effects of different doses of melatonin (ImM, 3mM, 5mM) were applied. In further series of experiments the effects of cumulative doses of melatonin receptor antagonist luzindole (10"7 M, 10"6 M, 10"5 M, 10"4 M) was tested on oxytocin-induced contractions. It was determined that both melatonin and luzindole had inhibitory effects on the oxytocin-induced contractions of myometrium and this effect of melatonin was involved both the effect on ion channels and on melatonin receptor subtypes.