We examined the participation of the intraluteal levels of progesterone (P 4 ) and prostaglandin F 2 (PGF 2 ) in the induction of luteolysis by LH and its relationship with the induction of the 20 -hydroxysteroid dehydrogenase activity (20 -HSD). Subcutaneous administration of four doses of 10 µg ovine LH (oLH) at 0800, 0900, 1000 and 1100 h on day 19 of pregnancy induced a decrease in the activity of the enzyme 3 -HSD 24 and 48 h after treatment and an increase in luteal 20 -HSD activity 48 h after oLH treatment when compared with control rats. Intraluteal and serum P 4 levels were lower than control values 24 and 48 h after oLH treatment, with a significant increase in luteal PGF 2 content and a decrease in corpus luteum (CL) weight 48 h after oLH treatment. Intrabursal ovarian (IB) treatment with an inhibitor of PG's biosynthesis (diclofenac) (70 µg/ovary) or P 4 (3 µg/ovary) on day 20 of pregnancy, prevented the increase in 20 -HSD activity observed 48 h after oLH treatment, without any effect on 3 -HSD activity. The IB administration of P 4 prevented the increase in intraluteal PGF 2 content induced by oLH treatment and the increases in 20 -HSD activity and intraluteal PGF 2 content observed in control animals on day 21 of pregnancy. The inhibition of PG biosynthesis also prevents the decrease in intraluteal and serum P 4 level induced by oLH. These results provide good evidence of the important participation of intraluteal P 4 and PGF 2 on the oLH-induced luteolysis in pregnant rats. We also found that P 4 produced by the CL is involved, in part, in the regulation of luteal PG synthesis. Thus, the early decline in 3 -HSD activity and the consequent fall in intraluteal P 4 content, may trigger the synthesis of PGs and thereafter the increase in luteal 20 -HSD activity to establish luteolysis.

Nuclear factor kappa B (NF B) is an important intracellular conveyor of extracellular signals and modulates a number of gene responses. Due to the potential significance of NF B in regulating ovarian gene expression, we examined in the rat: (i) whether NF B is activated and developmentally regulated in the corpus luteum (CL) throughout pregnancy; (ii) the proteins forming the NF B complex in luteal cells; and (iii) the role of this transcription factor in luteal function. Western analysis and immunohistochemistry revealed that p65 and p50 were highly expressed throughout pregnancy and were located in both the nucleus and cytoplasm of luteal cells. In addition, because NF B is maintained in the cytoplasm bound to I B, whose phosphorylation allows NF B translocation to the nucleus, we studied the developmental expression of phosphorylated and nonphosphorylated forms of I B . Western analysis revealed that I B was present and phosphorylated throughout pregnancy in the CL whereas by protein/DNA array and electromobility shift assays we found that luteal nuclear extracts bind to an NF B consensus sequence, and that the binding activity decreased along pregnancy. The specific binding was supershifted only by an anti-p65 antibody and not by antibodies against p50, p52, cRel, or RelB. Using day 4 postpartum ovaries, we found higher NF B binding activity in the newly formed CL than in old CL of pregnancy. Furthermore, NF B DNA binding activity was enhanced by prolactin in luteinized granulosa cells. In our first functional study, blockade of NF B/p65 binding to DNA with the sesquiterpene lactone helenalin in luteinized granulosa cells correlated with induction of cell death in a dose-dependent manner. In a second functional study, overexpression of NF B/p65 in luteal cells resulted in inhibition of 20 -hydroxysteroid dehydrogenase (20 HSD) promoter activity as well as endogenous 20 HSD mRNA expression. In summary, we have shown that: (i) NF B is expressed within the CL, primary luteinized granulosa cells, and a rat luteal cell line; (ii) NF B activation within the CL is developmentally regulated in pregnancy, depends on the age of the gland, and can be upregulated by prolactin; (iii) inhibition of NF B/p65 binding to an NF B DNA consensus sequence correlates with induction of cell death in ovarian luteinized granulosa cells; and (iv) overexpression of NF B in luteal cells inhibits 20 HSD gene expression. The results further support a role for NF B as a survival factor in the CL.