Changes in the metabolism of glucose, pyruvate, glutamine and glycine during maturation of cattle oocytes in vitro.

After maturation in vitro for 0, 6, 12, 18 or 24 h, the metabolism of radiolabelled glucose, glutamine, pyruvate and glycine by individual cattle oocytes was measured for 3 h. The metabolism of glucose through the Embden-Meyerhof (1.77-2.66 pmol per oocyte per 3 h) and pentose-phosphate (0.39-0.75 pmol per oocyte per 3 h) pathways was low and did not change over time. The oxidative metabolism of glucose carbon through the Krebs cycle was low throughout maturation, but increased significantly (P < or = 0.05) at 6 h (0.41 pmol per oocyte per 3 h) and 18 h (0.69 pmol per oocyte per 3 h). Pyruvate, glutamine and glycine metabolism in the Krebs cycle increased during culture. Pyruvate metabolism increased significantly from 0 h (17.3 pmol per oocyte per 3 h) to 6 h (23.3 pmol per oocyte per 3 h) and reached a maximum at 12 h (30.8 pmol per oocyte per 3 h). Glutamine metabolism was unchanged from 0 to 12 h (0.89 pmol per oocyte per 3 h), and then increased significantly at 18 h (2.25 pmol per oocyte per 3 h). Glycine metabolism increased significantly from 6 h (0.21 pmol per oocyte per 3 h) to 12 h (0.46 pmol per oocyte per 3 h) and reached a maximum at 18 h (0.68 pmol per oocyte per 3 h). The results suggest that oxidative metabolism increases, and is the major site of cellular energy production, during maturation of the cattle oocyte in vitro.