Enzyme activities and maturation in unstimulated and exogenous gonadotropin-stimulated human oocytes

With the advent of new techniques of human in vitro fertilization (IVF), identifying parameters of oocyte quality to allow selection of those most likely to fertilize becomes crucial. Morphology of oocytes, which correlates positively with biological performance, is the currently utilized classification criterion. However, biological links between form and function are tenuous, and underlying mechanisms remain elusive. We investigated whether biochemical activation is quantitatively associated with the stages of maturation in ova obtained from patients undergoing gynecologic surgery during unstimulated cycles and women undergoing IVF after exogenous gonadotropin stimulation. Changes in selected enzymes from protein, lipid, and carbohydrate metabolism (hexokinase, phosphoglucomutase, glycogen synthetase, uridine diphosphoglucose pyrophosphorylase, glucose-6-phosphate dehydrogenase, cytosolic thiolase, beta-hydroxyacyl-CoA dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) were determined simultaneously, in individual oocytes, utilizing a highly sensitive biochemical methodology. Several enzyme activities paralleled maturation grade and were higher in stimulated oocytes after correction for grade. These biochemical findings quantify metabolic and functional changes that increase as ova mature, possibly contributing to their reproductive performance.