Is tumor necrosis factor alpha a trigger for the initiation of endometrialprostaglandin F-2 alpha release at luteolysis in cattle?

To determine the physiological significance of tumor necrosis factor alpha (TNF alpha) in the regulation of luteolytic prostaglandin (PC) F-2 alpha re lease by the bovine endometrium, the effect of TNF-alpha on PGF(2 alpha) ou tput by the endometrial tissues in vitro was investigated and compared with the effect of oxytocin (OT), Furthermore, the presence of specific recepto rs for TNF alpha in the bovine endometrium during the estrous cycle was det ermined. Endometrial slices (20-30 mg) taken from six stages of the estrous cycle (estrus: Day 0; early I: Days 2-3; early II: Days 5-6; mid-: Days 8- 12; late: Days 15-17; and follicular: Days 19-21), as determined by macrosc opic examination of the ovaries and uterus, were exposed to TNF alpha (0.06 -6 nM) and/or OT (100 nM), OT stimulated PGF(2 alpha) output at the follicu lar stage and at estrus (P < 0.001), but not at the late luteal stage. On t he other hand, the stimulatory effects of TNF alpha on PGF(2 alpha) output were observed not only at the follicular stage but also at the late luteal stage (P < 0.001), When the endometrial tissues at late luteal stage were s imultaneously exposed to TNF alpha (0.6 nM) and OT (100 nM), the stimulator y effect on PGF(2 alpha) output was higher than the effect of TNF alpha or OT alone (P < 0.05). Specific binding of TNF alpha to the bovine endometria l membranes was observed throughout the estrous cycle. The concentration of TNF-alpha receptor at the early I luteal stage was less than the concentra tions at other luteal stages (P < 0.01). The dissociation constant (K-d) va lues of the endometrial membranes were constant during the estrous cycle. T he overall results lead us to hypothesize that TNF alpha may be a trigger f or the output of PGF(2 alpha) by the endometrium at the initiation of luteo lysis in cattle.