Roles of Tumor Necrosis Factor-(alpha) of the Estrous Cycle in Cattle: An In Vivo Study

We have suggested in a previous in vitro study that tumor necrosis factor-(alpha) (TNF(alpha)) plays a role in the initiation of luteolysis in cattle. The aim of the present study was to examine the influence of different doses of TNF(alpha) on the estrous cycle in cattle by observing the standing behavior and measuring peripheral concentrations of progesterone (P4) during the estrous cycle. Moreover, we evaluated the secretion of P4, oxytocin (OT), nitric oxide (NO), and luteolytic (prostaglandin F2(alpha) [PGF2(alpha)] and leukotriene C4 [LTC4]) and luteotropic (PGE2) metabolites of arachidonic acid in peripheral blood plasma as parameters of TNF(alpha) actions. Mature Holstein/Polish black and white heifers (n = 36) were treated on Day 14 of the estrous cycle (Day 0 = estrus) by infusion into the aorta abdominalis of saline (n = 8), an analogue of PGF2(alpha) (cloprostenol, 100 µg; n = 3) or saline with TNF(alpha) at doses of 0.1 (n = 3), 1 (n = 8), 10 (n = 8), 25 (n = 3), or 50 µg (n = 3) per animal. Peripheral blood samples were collected frequently before, during, and up to 4 h after TNF(alpha) treatment. After Day 15 of the estrous cycle, blood was collected once daily until Day 22 following the first estrus. Lower doses of TNF(alpha) (0.1 and 1 µg) decreased the P4 level during the estrous cycle and consequently resulted in shortening of the estrous cycle (18.8 ± 0.9 and 18.0 ± 0.7 days, respectively) compared with the control (22.3 ± 0.3 days, P < 0.05). One microgram of TNF(alpha) increased the PGF2(alpha) (P < 0.001) and NO (P < 0.001) concentrations and decreased OT secretion (P < 0.01). Higher doses of TNF(alpha) (10, 25, 50 µg) stimulated synthesis of P4 (P < 0.001) and PGE2 (P < 0.001), inhibited LTC4 secreton (P < 0.05), and consequently resulted in prolongation of the estrous cycle (throughout 30 days, P < 0.05). Altogether, the results suggest that low concentrations of TNF(alpha)activate corpus luteum function and prolong the estrous cycle in cattle.