Interleukin-1 receptor antagonist expression in the equine endometrium during the peri-implantation period

To identify factors involved in the establishment of pregnancy in the mare, endometrium was collected from day 13 (day 0 = day of ovulation) cyclic and day 13, 19, and 25 pregnant animals. From initial cDNA subtraction studies, interleukin-1 receptor antagonist (IL-1RN) mRNA was found as a candidate molecule expressed uniquely in the pregnant endometrium. Expression of IL-1RN mRNA was markedly increased in day 19 and 25 gravid endometrium. In situ hybridization analysis revealed that IL-1RN mRNA was localized to the glandular epithelium. Interleukin-1 receptor antagonist (IL-1RN) protein was found in the extracts of day 25 gravid endometrium and was immunochemically localized to the glandular epithelium-luminal cavity of the pregnant uterus. High concentrations of estradiol-17 beta (E-2) weredetected in day 25 conceptUses. Concentrations of E-2 were higherin the gravid endometrial portion than in other endometrial regions. On the other hand, progesterone concentrations did not differ among endornetrial samples analyzed. Furthermore, the expression of IL-lRN ntRNA was up-rcgulated in endoinetrium culture samples treated with 10 ng/mL E-2 and 10 ng/mL progesterone. In the analysis of related gene expression, increased amounts of IL-1 alpha and IL-6 mRNA were also found in the day 25 gravid endornetrium; however, these expressions in endometrial culture samples were not up-regulated by the steroid treatment. These results indicate that expression of IL-1RN in the endornetrium is tikely regulated by E-2 and progesterone and suggest that IL-1RN regulates the degree of IL-1 signal transduction and thereby plays an important role in the establishment of equine pregnancy. (C) 2008 Elsevier Inc. All rights reserved.