Abstract
Mammalian oviduct acts as a reservoir for spermatozoa and provides an environment in which they may compete for the opportunity to fertilize the oocyte. Whilst in the oviduct spermatozoa undergo capacitation essential for fertilization. Sperm-oviduct interaction is essential for sperm capacitation and is a tightly regulated process influenced by the local microenvironment. Previously we reported that the endocannabinoid anandamide (AEA) regulates sperm release from epithelial oviductal cells by promoting sperm capacitation. The aims of this work were to measure the AEA content and to characterize the main AEA metabolic pathway in the bovine oviduct and determine how these change through the oestrous cycle. In this study, the levels of AEA and two other N-acylethanolamines, N-oleoylethanolamine and N-palmitoylethanolamine, were measured in bovine oviduct collected during different stages of oestrous cycle by ultra high performance liquid chromatography tandem mass spectrometry. Results indicated that intracellular oviductal epithelial levels of all three N-acylethanolamines fluctuate during oestrous cycle. Anandamide from oviductal fluid also varied during oestrous cycle, with the highest values detected during the periovulatory period. Endocannabinoid levels from ipsilateral oviduct to ovulation were higher than those detected in the contralateral one, suggesting that levels of oviductal AEA may be regulated by ovarian hormones. The expression and localization of N-acylethanolamines metabolizing enzymes in bovine oviduct were also determined by RT-PCR, Western blot, and immunohistochemistry but no change was found during the oestrous cycle. Furthermore, nanomolar levels of AEA were detected in follicular fluids, suggesting that during ovulation the mature follicle may contribute to oviductal AEA levels to create an endocannabinoid gradient conducive to the regulation of sperm function for successful fertilization.
Highlights
The oviduct plays a key role in the physiology of reproduction by providing a beneficial environment for gamete maturation and transport, fertilization and early embryo development during its subsequent passage to the uterus
We found that arachidonoylethanolamide or anandamide (AEA), OEA and PEA levels fluctuated during the oestrous cycle, suggesting that oviductal NAEs concentrations could be controlled by sex hormones
We have previously reported that AEA is a key molecule involved in the regulation of sperm release from oviductal epithelia by promoting sperm capacitation in bovines [26,27,40]
Summary
The oviduct plays a key role in the physiology of reproduction by providing a beneficial environment for gamete maturation and transport, fertilization and early embryo development during its subsequent passage to the uterus. It acts as a functional sperm reservoir providing an environment where these compete for the fertilization of the oocyte. Some molecules such as, glycosaminoglycans, present in oviductal secretions play a role in these sperm-oviduct interactions and bovine sperm capacitation [5,6,7,8].
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