The precise regulatory mechanisms of cyclic oviductal contraction in the cow are unclear. The purpose of this study was to evaluate the effect of luteinizing hormone (LH), steroids, prostaglandins (PGs) and peptides on the oviductal contraction and secretion of PGs and endothelin (ET-1). In addition, the cyclic expression of mRNA for ET-1 and its receptors (ET-R) was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). In the in vitro microdialysis study, an infusion of LH alone or in combination with progesterone (P(4)), estradiol-17beta (E(2)) and/or ET-1 stimulated pronounced release of PGE(2), PGF(2alpha) and ET-1 in the oviducts from cows in the follicular and postovulatory phases. The addition of LH, LH+P(4)+E(2) and/or ET-1 to the medium increased the amplitude of oviductal contraction. However, oxytocin (OT) completely blocked the responses of oviductal secretion and contraction. In contrast, these substances did not show any effect in the oviducts from cows in the mid luteal phase. Similar expression patterns of mRNA encoding for ET-R type A and type B were found, which were highest during the postovulatory phase, lower during the luteal phase, with the lowest expression during the follicular phase. We suggest that the preovulatory LH surge, together with increasing E(2) levels from the Graafian follicle and a basal P(4) from regressing corpora lutea (CL), stimulates maximum oviductal production of PG and ET-1, resulting in oviductal contraction for a rapid transport of gametes. OT released from the newly-formed CL may block these mechanisms, and slow contractions for transport of the embryo to the uterus.
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