Interleukin-1β system in the oviducts of pigs during the oestrous cycle and early pregnancy.

Interleukin-1β (IL-1β) acts throughout the IL-1β system, which contains IL-1β and the IL-1β receptor (IL-1R), accessory protein (IL-1RacP), and receptor antagonist (IL-1Ra). In pigs, the expression of the members of the IL-1β system was documented in uterine tissues during the oestrous cycle and early pregnancy, as well as in embryos harvested during the peri-implantation period. In the oviducts of non-gravid and gravid pigs, the expression of the IL-1β system is unknown. Thus, in this study, the expression of the IL-1β system was examined in porcine oviducts harvested on days 2-3 to 18-20 of the oestrous cycle and on days 2-3 to 15-16 of pregnancy. The expression of IL-1β, IL-1R and IL-1RacP mRNAs in oviducts increased during the mid-luteal phase of the oestrous cycle, whereas the expression of IL-1Ra mRNA increased only during the early luteal phase, e.g., on days 2-3 of the oestrous cycle. Low expression of IL-1β and IL-1Ra mRNAs was observed during the follicular phase of the oestrous cycle. In gravid pigs, the expression of IL-1β, IL-1Ra and IL-1R mRNAs decreased (P < 0.05) from days 2-3 to 15-16 of pregnancy, whereas IL-1RacP mRNA expression did not change in pregnant pigs (P > 0.05). Significantly greater expression of the IL-1β system mRNAs was demonstrated in oviducts harvested on days 2-3 of pregnancy vs. the respective days of the oestrous cycle. On days 2-3 of pregnancy, compared to respective days of the oestrous cycle, the quantity of IL-1β protein was decreased (P < 0.05) in the ampulla and isthmus, while the quantity of IL-1Ra (only in the ampulla) and IL-1RacP proteins (in the ampulla and isthmus) were increased. The concentration of IL-1β in oviductal flushings did not change (P > 0.05) in non-pregnant pigs, and it was greater (P < 0.05) on days 2-3 of pregnancy vs. the respective days of the oestrous cycle. Therefore, the presence of embryos in oviducts on days 2-3 after mating may influence the oviductal expression of the members of the IL-1β system, determining the action of IL-1β, which may be considered to be the earliest sign of pregnancy in pigs.