78 THE PERIOVULATORY ENDOCRINE MILIEU AFFECTS THE OXIDATIVE STRESS CONTROL ON ENDOMETRIUM OF COWS

Acknowledging that the local oxidative profile (pro or antioxidant) may influence the control of very specific mechanisms such as intracellular signalling as well as the unspecific damage caused by oxidative stress, it is proposed that the balance between reducing and oxidative activities of the uterine environment (i.e. the REDOX profile) is regulated by exposure to ovarian steroids. The aim of this study was to verify the effect of the periovulatory endocrine milieu on concentrations of reactive oxygen species (ROS), activity of antioxidant enzymes, and lipid peroxidation profile on the endometrial tissue of cows in early diestrus. Eighty-three cyclic, nonlactating Nelore cows received an intravaginal progesterone (P4) device and an injection of oestradiol benzoate (E2) on Day –10. Animals were divided into 2 groups to receive sodium cloprostenol (PGF; large follicle group; LFG; N = 42) or not (small follicle group; SFG; N = 41) on Day –10. Progesterone devices were removed and prostaglandin F2α was injected between Day –2.5 and Day –1.75 in cows from LFG, and between Day –1.5 and Day –1.25 in cows from SFG. Ovulation was induced with GnRH on Day 0. Progesterone and oestradiol plasma concentrations were quantified. Animals were slaughtered on Day 7, when endometrial tissue was collected. A subgroup of ovulated cows (n = 9 per group) was selected to assess the activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Furthermore, the content of reduced glutathione (GSH) and ROS by spectrofluorometry and lipid peroxidation by assessment of malondialdehyde concentrations were determined. Statistical comparisons between groups were performed by ANOVA (Statistica 4.5; StatSoft Inc., Tulsa, OK, USA). Maximum diameter of the preovulatory follicle (mean ± s.e.m.; 13.36 ± 0.29 v. 11.11 ± 0.33 mm, respectively; P < 0.01), plasma concentrations of P4 on Day 7 (3.71 ± 0.25 v. 2.62 ± 0.26 ng mL–1; P < 0.01) and E2 on Day 0 (2.94 ± 0.28 v. 1.27 ± 0.2 pg mL–1; P < 0.01) were greater in LFG compared with SFG. The SFG showed lower enzymatic activity for CAT (0.79 ± 0.09 v. 0.5 ± 0.07 U mg–1 of protein; P < 0.01) and GPx (2.43 ± 0.39 v. 2.0 ± 0.35 nmol of NADPH/min/mg of protein; P < 0.05) than LFG. Additionally, lipid peroxidation was increased in SFG (177.68 ± 46.46 v. 255.71 ± 40.64 nmol of MDA/g of tissue; P < 0.01), similarly to SOD activity (37.76 ± 3.95 v. 44.77 ± 7.66 IU; P < 0.05). Concentrations of ROS and GSH were not different between groups. In conclusion, the periovulatory endocrine environment alters antioxidant mechanisms in the endometrium of cows in early diestrus. Specifically, it is proposed that the greater antioxidant activity observed on the LFG provided an environment that was less prone to lipid peroxidation than that from the SFG. The increase in SOD activity suggests a compensatory mechanism triggered by an environment potentially more oxidative observed on the SFG. The REDOX profile observed on the experimental groups may be associated with higher fertility observed in cows with higher E2 and P4 concentration during the proestrus and early diestrus, respectively. We acknowledge support from CNPq, FAPESP; Ourofino, CCPS-USP.