ABSTRACT
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, ,ovary , placenta and uterus. It has a relaxant effect on smooth muscles of the stomach and blood vessels. However , its effect and mechanism of action on the smooth muscle of the uterus are still controversy

Aim of the study : This study was designed to demonstrate the in vitro effects and mechanism of action of apelin on rat uterine reactivity.

Material and Methods: 60 adult albino rats (48 females and 12 males). Female rats were randomly divided into non- pregnant, pregnant (day 6 and day 19 ) and 1st day postpartum groups. The effects of apelin (1,10 and 100 nmol /L) on spontaneous reactivity of isolated uterine strips were studied. Also, apelin (100 nmol/L) in the presence of L-NAME , apamin and Glibenclamide was investigated.
Results: Apelin exerted a significant dose dependent reduction in frequency and amplitude of spontaneous uterine contraction. This reduction was significantly more potent on day 6 than that in both non pregnant and pregnant rats on day 19. Also , it was significantly and nearly completely abolished in the presence of L-NAME, but it was significantly and partially decreased in the presence of (Apamin) and (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.