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The influence of oxygen tension on cumulus cell viability of canine COCs matured in high-glucose medium.

High in vitro oxygen (O(2)) tensions are associated with enhanced levels of reactive oxygen species and cumulus oocyte complex (COC) apoptosis. The objective of this study was to determine the influence of O(2) tension on cumulus cell (CC) viability from canine oocytes. Cumulus oocyte complexes were distributed into three groups (CG, T20 and T5) and two O(2) tension levels (20% and 5%). The control group (CG) was matured in vitro in a humidified atmosphere with 5% CO(2) in air in TCM199 with 26.19 mM sodium bicarbonate, 10% (v/v) foetal calf serum (FCS), 0.10 mM gentamicin, 0.20 mM pyruvic acid, 20 microg/ml oestradiol, 0.5 microg/ml follicle-stimulating hormone, 0.03 IU/ml human chorionic gonadotropin, and 1.0 microg/ml human somatotropin. Groups T20 and T5 were matured under 20% or 5% O(2) tensions respectively in a high-glucose medium, without FCS. T20 and T5 were as CG, and supplemented with 0.1% Polyvinyl Alcohol, and 5.5 mM glucose. After 48 h of IVM, CCs from COCs were stained with propidium iodide (1.50 mM). The results showed that viability of CCs (cytoplasmic features and nuclear morphological integrity) was different for the three groups. Rates of apoptosis were at 57.9% (521/900) for CG, 54.4% (490/900) for T20 and 38.9% (350/900) for T5 (p < 0.001). Predominant features in apoptotic cells (n = 1361) were DNA nuclear fragments (94.0%). It was concluded that CCs of canine COCs cultured in high-glucose medium showed significantly less apoptosis than those cultured in medium with FCS. Low O(2) tension was efficient in reducing apoptosis in canine CCs.