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The objective of this study was to investigate tumor necrosis factor alpha (TNF-alpha) expression, the presence of functional TNF-alpha receptors, and expression of TNF receptor type I (TNF-RI) mRNA in the bovine corpus luteum (CL) during different stages of the estrous cycle. Reverse transcription (RT)-polymerase chain reaction (PCR) showed no difference in TNF-alpha mRNA expression during the estrous cycle. Concentrations of TNF-alpha in the CL tissue increased significantly from the mid to the late luteal stage and decreased thereafter (P < 0.05). An RT-PCR analysis showed higher levels of TNF-RI mRNA in CL of Days 3-7 than of other stages (P < 0.05). (125)I-TNF-alpha binding to the membranes of bovine CL was maximal after incubation at 38 degrees C for 48 h. The binding was much greater for TNF-alpha than for related peptides. A Scatchard analysis revealed the presence of a high-affinity binding site in the CL membranes collected at each phase of the estrous cycle (dissociation constant: 3.60 +/- 0.58-5.79 +/- 0.19 nM). In contrast to TNF-RI mRNA expression, the levels of receptor protein were similar at each stage of the estrous cycle. When cultured cells of all luteal stages were exposed to TNF-alpha (1-100 ng/ml), TNF-alpha stimulated prostaglandin F(2alpha) and prostaglandin E(2) secretion by the cells in a dose-dependent fashion (P < 0.01), especially during the early luteal phase, although it did not affect progesterone secretion. These results indicate the local production of TNF-alpha and the presence of functional TNF-RI in bovine CL throughout the estrous cycle, and suggest that TNF-alpha plays some roles in regulating bovine CL function throughout the estrous cycle.
Sakumoto et al. (Sat,) studied this question.