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Apelin Induced Modulation of Uterine Contractility in Adult Albino Rats and its Possible Mechanisms of Action

Mansour SW, Asalah AK, Attia KI and El Sayed Mohammed S

Background: Apelin is an endogenous ligand for the G protein-coupled receptor APJ, The expression of both apelin and APJ has been detected in a variety of tissues including heart, brain, ovary, placenta and uterus. It has a relaxant effect on smooth muscles of the stomach and blood vessels. However, its effect on the smooth muscle of the uterus is still controversy and its mechanism of is not fully investigated despite some author report that NO may be involved. Aim of the study: This study was designed to demonstrate the in vitro effects of apelin on spontaneous contraction of pregnant and non-pregnant rat uterus and to investigate its possible mechanism/s of action. Material and methods: Sixty adult albino rats (48 females and 12 males). Female rats were randomly divided into nonpregnant, pregnant (day 6 and day 19) and 1st day postpartum groups. The effects of apelin (1,10 and 100 nmol/L organ bath fluid) on spontaneous contractile activity of isolated uterine strips were studied. Also, the effect of apelin on uterine strips isolated from pregnant rats (100 nmol/L) was investigated in the presence of L-NAME, apamin and Glibenclamide. Results: Apelin exerted a significant dose dependent reduction in frequency and amplitude of spontaneous uterine contraction. This utero-relaxant effect of apelin was significantly more potent on day 6 of gestation than that in both non pregnant rats and pregnant rats on day 19 of gestation. Apelin induced utero-relaxant effect was significantly and nearly completely abolished in the presence of L-NAME, but it was significantly and partially decreased in the presence of small conductance-Ca2+ activated K+ channel blocker (Apamin) and ATP sensitive K+ channel blocker (Glibenclamide). Conclusion: Apelin has a potent utero-relaxant effect which is greater in early pregnancy compared with late pregnancy. Thus Apelin may be a promising tocolytic drug.