Melatonin inhibits spontaneous and oxytocin-induced
contractions of rat myometrium in vitro by Ahmet Ayar, Selim Kutlu, Bayram Yilmaz & Haluk Kelestimur
Keywords: melatonin, myometrium, isometric contraction,
March 28, 2000
Accepted: June 4, 2001
The aim of this study was to investigate the effects of melatonin
on spontaneous and oxytocin-induced contractility of pregnant
and non-pregnant rat myometrium in vitro.
DESIGN: Myometrial strips were removed from virgin or late
pregnant (21 days gestation) Wistar rats following decapitation
and placed in an organ bath containing Krebs solution
at 37°C and pH 7.4, constantly bubbled with 95% oxygen-5%
carbon dioxide and isometric contractions were recorded. Effects
of cumulative concentrations of melatonin (0.1 to 10 mM)
on spontaneous and oxytocin-induced contractions were studied.
Possible involvement of Ca2+-activated K+ channels in inhibitory
actions of melatonin was investigated by using apamin (100
RESULTS: Melatonin inhibited spontaneous and oxytocin-induced
contractions of myometrium from both virgin and late pregnant
rats in a dose-dependent manner. After inhibition of oxytocin-induced
contractions by melatonin, application of prostaglandin F2a
(1 mM) but not high KCl (30mM)
containing solution initiated contractile activity. Inhibitory
response induced by melatonin (13mM)
was not affected by apamin (100 nM).
CONCLUSIONS: Data from this study demonstrates that melatonin
inhibits spontaneous and oxytocin-induced contractions of
myometrium from pregnant and non-pregnant rats. Although the
exact mechanism is not clear, melatonin-induced inhibition
of myometrial contractions may results from its interactions
with Ca2+ channels.