Effects of tumor necrosis factor-α on secretion of prostaglandins E₂ and F_2α in bovine endometrium throughout the estrous cycle

To determine the physiological significance of tumor necrosis factor-α (TNFα) in the regulation of endometrial prostaglandin (PG) release in cattle, we investigated the effects of TNFα on the secretion of PGE₂ and PGF_2α by bovine endometrium during the estrous cycle. Bovine uteri were classified into six stages (estrus: Day 0, early luteal I: Days 2 to 3, early luteal II: Days 5 to 6, mid-luteal: Days 8 to 12, late luteal: Days 15 to 17 and follicular: Days 19 to 21). After 1 h of pre-incubation, endometrial tissues (20 to 30 mg) were exposed to 0 or 0.6 nM TNFα for 4 h. The PGE₂ concentrations in the medium were higher in the luteal stages than in the follicular stage and in estrus. In contrast, PGF_2α concentrations were higher in the follicular stage and in estrus than in the luteal stages. The ratio of the basal concentrations of PGE₂ and PGF_2α (PGE₂/PGF_2α ratio) was higher in the luteal stages than in the follicular stage and in estrus. Although TNFα stimulated both PGE₂ and PGF_2α secretion during the entire period of the estrous cycle, the level of stimulation of TNFα on PGE₂ output by the bovine endometrium does not show the same cyclical changes as that shown on PGF_2α output. The stimulation of TNFα resulted in a decrease in the PGE₂/PGF_2α ratio only in the late luteal stage. Furthermore, TNFα stimulated PGE₂ secretion in stromal, but not epithelial cells. The overall results suggest that TNFα is a potent regulator of endometrial PGE₂ secretion as well as PGF_2α secretion during the entire period of estrous cycle, and that TNFα plays different roles in the regulation of secretory function of bovine endometrium at different phases of the estrous cycle.