Luteal P4 synthesis in early pregnant gilts after induction of estrus with PMSG/hCG

• Induction of estrus in prepubertal gilts with PMSG/hCG decreased StAR, CYP11A1, and 3βHSD expression in the CL.
• PMSG/hCG injections decreased P4 concentrations in luteal tissue and blood serum.
• LHR and ESR1 mRNA expression was up-regulated in gonadotropin-treated gilts.

The present study was designed to examine whether an estrus induction with gonadotropins could affect luteal P4 synthesis in early pregnant gilts. Sixteen prepubertal gilts received 750 IU of PMSG and 500 IU of hCG 72 h later. Prepubertal gilts in the control group (n = 17) were observed daily for estrus behavior. All gilts were inseminated in their first estrus. Corpora lutea (CLs) were collected on days 10, 12 and 15 of pregnancy and analyzed for (1) the mRNA and protein expression of steroidogenic acute regulatory protein (StAR), cytochrome P450 family 11 subfamily A polypeptide 1 (CYP11A1), and 3β-hydroxysteroid dehydrogenase (3βHSD); (2) the tissue concentration of P4; and (3) the mRNA expression of luteinizing hormone receptor (LHR) and estrogen receptors (ESR1 and ESR2). Additionally, P4 concentration was analyzed in blood serum of all animals. PMSG/hCG injections to induce estrus decreased mRNA expression of StAR, CYP11A1 and 3βHSD on day 10 and CYP11A1 on day 12 of pregnancy compared with the control group, while CYP11A1 and 3βHSD proteins were down-regulated on day 10 in the hormonally-treated gilts. Concentrations of P4 in luteal tissue and blood serum were also lower in animals after gonadotropin-induced estrus. In contrast, LHR and ESR1 mRNA expression was greater in PMSG/hCG-treated than control gilts on day 15 of gestation. In conclusion, induction of estrus with a PMSG/hCG protocol in prepubertal gilts impaired expression of the luteal P4 synthesis system. Low P4 content may, in turn, induce local mechanisms involving LHR and ESR1 expression to support CL function.