Cumulus expansion and glucose utilisation by bovine cumulus-oocyte complexes during in vitro maturation: the influence of glucosamine and follicle-stimulating hormone.

Glucose is an important metabolite and its presence during in vitro oocyte maturation (IVM) can have profound effects on the oocyte's developmental capacity. We have demonstrated that glucose uptake increases over a 24 h IVM period, with most accounted for as l-lactate production. However, as maturation proceeds, l-lactate production remains constant, suggesting an alternative role for glucose metabolism. We hypothesised that in the latter stages of oocyte maturation, glucose not accounted for by l-lactate production is utilised for FSH-stimulated extracellular matrix (ECM) synthesis. To examine precursor utilisation for synthesis of ECM, bovine cumulus-oocyte complexes (COCs) were matured in +/- FSH and/or glucosamine (an alternative substrate of matrix components). Measurements included COC diameters, glucose consumption and l-lactate production in spent media and [U-(14)C]glucose incorporation into ECM. FSH significantly stimulated both diameter and glucose consumption during 20-24 h maturation compared with unstimulated complexes, although co-incubation with glucosamine and FSH decreased total glucose consumption 1.7-fold compared with FSH alone (P < 0.05). Furthermore, there was a linear relationship between glucose and l-lactate metabolism in the presence of glucosamine, suggesting that the majority of glucose was being utilised for l-lactate production via glycolysis. In the presence of glucosamine, twofold less [U-(14)C]glucose was incorporated into matrix compared with COCs cultured without glucosamine. These results support the hypothesis that there is a link between glucose and glucosamine uptake in FSH-stimulated ECM synthesis. Furthermore, glucose has multiple fates within the COC during maturation and levels of utilisation are dependent on the composition of the maturation environment.