Interleukin (IL)‐1 in rat parturition: IL‐1 receptors 1 and 2 and accessory proteins abundance in pregnant rat uterus at term – regulation by progesterone

The role of interleukin‐1 (IL‐1), a pro‐inflammatory cytokine, in parturition is typically noted by changes in its concentrations. Studying the expression of its receptor family, IL‐1 receptor (IL‐1R) 1, IL‐1R2, IL‐1R accessory protein (IL‐1RAcP), and its predominantly brain isoform, IL‐1RAcPb, during late gestation in the uterus in the Long‐Evans rat is another. We assessed changes in their mRNA and protein relative abundance in the uterus and compared IL‐1RAcP and IL‐1RAcPb mRNA abundance in uterus, cervix, ovaries, placenta, and whole blood of Long‐Evans rats during late gestation or in RU486 and progesterone‐treated dams using quantitative real‐time PCR and western immunoblotting. IL‐1R1, IL‐1RAcP, and IL‐1RAcPb mRNA abundance significantly increased in the uterus at delivery whereas IL‐1R2 mRNA abundance significantly decreased. IL‐1R1 protein increased at term and IL‐1R2 protein decreased at term compared to nonpregnant uteri. IL1‐RAcPb mRNA abundance was less than IL‐1RAcP, but in the lower uterine segment it was the highest of all tissues examined. RU486 stimulated preterm delivery and an increase in IL‐1R1 mRNA abundance whereas progesterone administration extended pregnancy and suppressed the increase in IL‐1R1. These data suggest that changes in uterine sensitivity to IL‐1 occur during late gestation and suggest another level of regulation for the control of delivery. The roles for IL‐1RAcP and IL‐1RAcPb need to be determined, but may relate to different intracellular signaling pathways.