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

Abstract

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.