Acquisition of Luteolytic Capacity: Changes in Prostaglandin F _2α Regulation of Steroid Hormone Receptors and Estradiol Biosynthesis in Pig Corpora Lutea

The pig corpora lutea (CL) acquires luteolytic capacity at about Day 13 of the estrous cycle, after which luteolysis occurs in response to prostaglandin F_2α (PGF_2α) treatment. We postulated that differences in transcription factors such as the steroid hormone receptors may be responsible for the differences in PGF_2α-induced gene expression after acquisition of luteolytic capacity. In these studies, we evaluated the effect of PGF_2α on luteal expression of receptors for progesterone (nuclear and membrane progesterone receptor [PR]), estradiol (ERα and ERβ), glucocorticoid, androgens, and two enzymes in estradiol synthesis (P450-17α and aromatase). Two experiments were conducted to examine the early (0.5 h, experiment I) and late (10 h, experiment II) effects of PGF2α on the expression of these receptors in CL with (Day 17) or without (Day 9) luteolytic capacity. PGF_2α decreased ERα mRNA (35%) and increased ERβ mRNA (558%) and protein (376%) only in Day 17 CL and not Day 9. The estradiol biosynthetic pathway was upregulated by PGF_2α in Day 17 CL but not Day 9 CL, with a dramatic increase in aromatase mRNA and luteal estradiol content. Nuclear PR was not affected by PGF_2α, but was greater (176%) in Day 9 CL, while a putative membrane PR was greater (156%) in Day 17 than Day 9 CL. There were no detectable changes in glucocorticoid or androgen receptor mRNA. Thus, luteolytic capacity is associated with upregulation of estradiol biosynthesis, which in conjunction with increased ERβ expression and altered PR expression may promote luteolysis in the pig CL.