Endometrial and conceptus response to exogenous progesterone treatment in early pregnant gilts following hormonally-induced estrus.

The aim of the study was to determine how supplementation with exogenous progesterone (P4) affects the expression of genes important for endometrial receptivity and conceptus development during the peri-implantation period in pigs. Gilts with PMSG/hCG-induced first estrus received daily injections of corn oil (CO; n=7) or P4 (n=7) on days 3 to 10 after insemination. The dose of P4 was 25mg/100kg BW on days 3 and 4 of gestation, then increased to 50mg/100kg BW on days 5 to 10. Blood samples were collected each day to monitor concentrations of circulating P4. Animals were slaughtered on day 12 of pregnancy to obtain endometrial tissue, conceptuses, and uterine luminal flushing (ULF). Gilts in the P4 group had consistently greater P4 concentrations in the blood compared with controls. Treatment of gilts with P4 increased uterine weight and enhanced total protein content and 6-keto PGF1α (a PGI2 metabolite) content in the uterine lumen. Moreover, injections of gilts with P4 increased the expression of prostaglandin endoperoxide synthase 2, microsomal PGE2 synthase and vascular endothelial growth factor A mRNA in the endometrium, but had no effect on gene expression in conceptuses. These results indicate that P4 supplementation stimulated the secretory activity of the endometrium and increased the expression of genes responsible for vascular function and luteotropic PGE2 synthesis, which are important components of successful pregnancy establishment in pigs. However, no effect of P4 treatment was detected in conceptuses.