Reproduction Abstracts

Oocyte–cumulus communication is essential for COC metabolism and oocyte developmental competence. Although the oocyte appears not to be absolutely required for cumulus expansion in cattle, it is not clear whether it influences this process. We tested the effects of oocytectomy on expansion and glucose metabolism of bovine COCs submitted to in vitro maturation (IVM). Follicles 3–8 mm were aspirated from abattoir ovaries and grades 1 and 2 COCs were selected. Intact COCs, oocytectomized COCs (OOXs), and OOXs added to denuded oocytes (OOXs+DOs; 1 DO/μl) were matured in groups of 20 (four replicates). IVM was performed at 38.5 °C; 5.5% CO₂ for 22 h in 96-well plates with 100 μl of TCM-199 supplemented with piruvate (22 μg/ml), amicacin (75 μg/ml), FSH (1 μg/ml), and BSA (4 mg/ml). After IVM, expansion degree was visually assessed (grades 1–3) and lactate and glucose concentrations were measured in the medium by dry chemistry. Oocytectomy did not prevent expansion but led to a lower percentage of structures with maximum expansion (grade 3; OOX: 66.25% vs COC: 81.6%). The addition of DOs stimulated expansion in OOXs, leading to values equivalent to those observed in intact COCs (83.75% fully expanded). Oocytectomy decreased glucose uptake (909.1, 669.2, and 732.3 pmol/COC/H for COCs, OOxs, and OOXs+DOS respectively) and lactate production (2210.2, 1409.1, and 1619.3 pmol/COC/H for COCs, OOXs, and OOXs+DOS respectively). Addition of DOs did not alter glucose uptake and lactate production of OOXs. These data suggest that the oocyte regulates expansion and glucose metabolism in bovine cumulus cells submitted to IVM. While the effects on expansion appear to be mediated by oocyte secreted factors, the regulation of cumulus metabolism appears to require direct oocyte–cumulus contact.