We have suggested in a previous in vitro study that tumor necrosis factor-alpha (TNFalpha) 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 TNFalpha 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 F2alpha [PGF2alpha] and leukotriene C4 [LTC4]) and luteotropic (PGE2) metabolites of arachidonic acid in peripheral blood plasma as parameters of TNFalpha 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 PGF2alpha (cloprostenol, 100 microg; n = 3) or saline with TNFalpha at doses of 0.1 (n = 3), 1 (n = 8), 10 (n = 8), 25 (n = 3), or 50 microg (n = 3) per animal. Peripheral blood samples were collected frequently before, during, and up to 4 h after TNFalpha treatment. After Day 15 of the estrous cycle, blood was collected once daily until Day 22 following the first estrus. Lower doses of TNFalpha (0.1 and 1 microg) 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 TNFalpha increased the PGF2alpha (P < 0.001) and NO (P < 0.001) concentrations and decreased OT secretion (P < 0.01). Higher doses of TNFalpha (10, 25, 50 microg) 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 TNFalpha cause luteolysis, whereas high concentrations of TNFalpha activate corpus luteum function and prolong the estrous cycle in cattle.

Abstract. The aim of this study was to examine whether active metabolites of phytoestrogens (equol and para-ethyl-phenol) inhibit sensitivity of bovine corpus luteum (CL) to luteinizing hormone (LH) and to auto/paracrine luteotropic factors (prostaglandin E2-PGE2 and prostaglandin F2α-PGF2α), and whether they influence pulsatile progesterone (P4) secretion by the bovine CL. In in vivo experiments, high levels of equol and para-ethyl-phenol were found in plasma and in the CL tissue of heifers and cows fed a soy bean diet (2.5 kg/animal/day), along with lower concentrations of P4 (P<0.05). Both Prostaglandins (PG) and LH strongly stimulated P4 secretion in cultured pieces of CL that were collected from cows fed a standard diet (P<0.01). There was no effect of PGs and LH on P4 stimulation in CLs obtained from cows fed a diet rich in soy bean. Finally, we examined whether active metabolites of phytoestrogens participated in regulation of pulsatile P4 secretion and LH-stimulated P4 secretion in vitro using a microdialysis system. Equol and para-ethyl-phenol had no effect on basic and pulsatile P4 secretion in CLs during 240 min of perfusion when compared to the control (P<0.05). However, they inhibited LH-stimulated P4 secretion (P<0.05). Phytoestrogens and their metabolites may disrupt CL function by inhibiting PG-and LH-stimulated P4 secretion. Key words: Phytoestrogens, Luteinizing hormone, Progesterone, Corpus luteum, Estrous cycle (J. Reprod. Dev. 52: [33][34][35][36][37][38][39][40][41] 2006) he corpus luteum (CL) is a reproductive gland that plays a role in regulation of the estrous cycle, fertility, and pregnancy [1]. The main function of the CL is secretion of progesterone (P 4 ), an important hormone for establishment of a successful pregnancy [2]. P 4 is secreted episodically from the bovine CL [3], and luteinizing hormone (LH) is one of the most potent regulators of synthesis and P 4 secretion from the bovine CL [4].The mechanisms controlling development, maintenance of the CL, and P 4 secretion involve many factors produced both, inside and outside the CL [1,5]. Besides pituitary hormones (LH and FSH), locally produced growth factors, peptides, steroids, and prostaglandins (PG) play important roles in bovine luteal function [1,4,5]. Moreover, the human [6], rat [7], porcine [8], and bovine CL [9] produce estradiol-17β (E 2 ). E 2 affects the secretory function of cultured bovine luteal cells [10] and the microdialyzed bovine CL in vitro [11]. Since estrogen receptors are present in the bovine CL [12], luteal E 2 and exogenous estrogens may play