LATE DIOESTRUS ACTH-INJECTION IN SHEEP DOES NOT CAUSE A DELAYED LUTEOLYSIS BUT AN OXIDATIVE STRESS CONDITION

This study aimed at investigating if simulated long-term stress during late diestrus has an impact on concentrations of progesterone and some markers of oxidative stress. Oestrous cycles of 30 non-pregnant, non-lactating Sarda ewes were synchronized using intravaginal prog- estin sponges (Chronogest, Intervet) for 14 days, and on the day of sponge removal 300 IU of PMSG was given im. After 14 days, 15 sheep (ACTH group) received twice daily (08.00 and 20.00 h) 0.5 mg of a synthetic ACTH (Synacthen Depot, Novartis) for 5 days, while the other 15 animals received saline and served as control (CTR). Blood was collected by jugular venipuncture every other day until ACTH administration and then daily for further 14 days. Cortisol concentrations was significantly higher in the ACTH group than in the CTR (p < 0.001). No significant differences were evidenced in progesterone concentration or oestrous cycles length (17.4 ± 3.5 vs 17.1 ± 3.4 days for ACTH and CTR groups, respectively). During ACTH administration, glutathione peroxidase activity tended to be lower in the ACTH group (p < 0.099). Total glutathione significantly decreased in the ACTH group (p < 0.01), whereas the oxidized form of glutathione was higher than in the CTR (p < 0.01). Superoxide dismutase activity increased after day 1 of treatment in the ACTH group compared to the CTR (p < 0.05). Conclusion: ACTH administration during the late diestrus neither modified progesterone concentrations nor delay luteolysis, whereas a clear alteration of scavenger systems for reactive oxygen species was evidenced (Sup- ported by MIUR [PRIN 2004]).