Phytoestrogen metabolites are much more active than phytoestrogens themselves in increasing prostaglandin F_2α synthesis via prostaglanin F_2α synthase-like 2 stimulation in bovine endometrium

Phytoestrogens have recently been suggested to be the cause of infertility by stimulating luteolytic prostaglandin (PG) F_2α secretion from endometrium in cattle. The purpose of this study was to examine the enzymatic and molecular mechanisms involved in the preferential induction of PGF _2α synthesis by phytoestrogens, and whether phytoestrogens influence endometrial cell viability. Cultured bovine endometrial epithelial and stromal cells were exposed to phytoestrogens (daidzein and genistein) and their metabolites (equol and p-ethyl phenol) for 24 h. Prostaglandin F _2α and PGE₂ were stimulated by phytoestrogens in both stromal and epithelial cells, with a preference for PGF_2α synthesis in epithelial cells (P < 0.001). Although RT-PCR and Western Blot analyses did not reveal the influence of phytoestrogens on either gene expression or protein level of cyclooxygenase-2 (COX-2) and PGE₂ synthase (PGES) in stromal and epithelial cells (P > 0.05), the stimulative effects of equol and p-ethyl phenol on PGF_2α synthase-like 2 (PGFSL2) gene expression and protein level were observed only in epithelial cells (P < 0.05). The same compounds did not affect PGFSL2 gene expression and protein in stromal cells (P > 0.05). Exposure to phytoestrogens and their metabolites decreased cell viability in both stromal and epithelial cells. Stromal cell viability decreased to 50% of the control and was more evident than that in epithelial cells (P < 0.001). The overall results suggest that infertility in cattle, caused by phytoestrogen-dependent preferential stimulation of luteolytic PGF_2α synthesis, is caused by increasing PGFSL2 in epithelial cells, and by decreasing stromal cell viability, which are the main source of luteotropic PGE₂ production.