Endothelin-1 system in the bovine oviduct: a regulator of local contraction and gamete transport.

Endothelin-1 (ET-1) is involved in the control of reproductive function. This study investigated the possible involvement of ET-1 in the regulation of oviductal contraction in the cow. The expression of mRNA for the ET-1 ligand and receptors was varied with the stage of the estrus cycle; highest expression occurred during the peri-ovulatory period and lower expression occurred during the luteal phase. As investigated by an in vitro microdialysis system implanted in the lumen of oviduct, the highest stimulatory effect on ET-1 secretion was observed with combined treatment of high estradiol-17beta (E2), low progesterone (P4) and luteinizing hormone (LH). Moreover, ET-1 augmented the stimulatory effect of P4, E2 and LH on the prostaglandin E2 and F2alpha release. Additionally, ET-1 increased the amplitude of in vitro contraction of oviducts from follicular and post-ovulatory phases, but not during the luteal phase. This was further intensified when ET-1 was combined with E2, P4 and LH. The results of the present study suggest that the elevated local ET-1 concentration with higher expression of its receptors during the peri-ovulatory period induces the high contractile activity of the oviduct, and at the same time a stimulation of prostaglandin production. Hence, the functional ET system in the oviduct is up-regulated during the peri-ovulatory period. In conclusion, the oviductal ET system enhances the release of contraction-related substances and modulates local contraction to optimize the oviductal transport of the gametes and embryo.