In vivo response of the corpus luteum to progesterone treatment of gilts during early gestation.

Supplementation of progesterone (P4) in pregnant gilts increases concentrations of circulating P4 and stimulates the secretory activity of the endometrium. In this study, there was examination of the consequences of exogenous P4 administration on luteal P4 content and the expression of genes related to the corpus luteum (CL) function. Gilts with gonadotropin-induced estrus were administered daily injections of corn oil (n = 8) or P4 (n = 8) on days 3 through 10 after insemination. The animals were slaughtered on day 12 of pregnancy to obtain corpora lutea for real-time polymerase chain reaction analyses of selected genes and for enzyme immunoassay of P4. Injections with P4 had no effect on the concentration of P4 and the relative abundance of mRNA transcripts of cholesterol transport-related proteins, steroidogenic enzymes, and receptors for luteotropic factors in the luteal tissue. The abundance of prostaglandin (PG) endoperoxide synthase 2, PGI2 synthase, PGI2 receptor, fibroblast growth factor 2, peroxisome proliferator-activated receptor γ, and tumor necrosis factor α receptor type I transcripts increased after P4 treatment. In contrast, the relative abundance of angiopoietin 2 mRNA decreased in response to P4 administration. In summary, P4 supplementation in pregnant gilts does not affect luteal steroidogenesis but modulates the abundance of factors related to vascular function. Given that the endometrium is the main target tissue for P4, an indirect uterine-mediated effect of exogenous P4 on CL function is likely.