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Acquisition of Luteolytic Capacity: Changes in Prostaglandin F₂ Regulation of Steroid Hormone Receptors and Estradiol Biosynthesis in Pig Corpora Lutea¹

Endocrinology-Reproductive Physiology Program and Department of Dairy Science, University of Wisconsin-Madison, Madison, Wisconsin 53706

The pig corpora lutea (CL) acquires luteolytic capacity at about Day 13 of the estrous cycle, after which luteolysis occurs in response to prostaglandin F₂ (PGF₂) treatment. We postulated that differences in transcription factors such as the steroid hormone receptors may be responsible for the differences in PGF₂-induced gene expression after acquisition of luteolytic capacity. In these studies, we evaluated the effect of PGF₂ on luteal expression of receptors for progesterone (nuclear and membrane progesterone receptor [PR]), estradiol (ER and ERß), glucocorticoid, androgens, and two enzymes in estradiol synthesis (P450-17 and aromatase). Two experiments were conducted to examine the early (0.5 h, experiment I) and late (10 h, experiment II) effects of PGF₂ on the expression of these receptors in CL with (Day 17) or without (Day 9) luteolytic capacity. PGF₂ decreased ER mRNA (35%) and increased ERß mRNA (558%) and protein (376%) only in Day 17 CL and not Day 9. The estradiol biosynthetic pathway was upregulated by PGF₂ 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 PGF₂, 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 ERß expression and altered PR expression may promote luteolysis in the pig CL.

¹ Supported by USDA-00-35203-9134, HD-32623, and an Advanced Opportunity Fellowship to F.J.D.

² Correspondence: Milo C. Wiltbank, Department of Dairy Science, University of Wisconsin-Madison, 1675 Observatory Drive, Madison, WI 53706. FAX: 608 263 9412; wiltbank{at}calshp.cals.wisc.edu

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