Effects of luteinizing hormone on glucose metabolism in cumulus- enclosed bovine oocytes matured in vitro

Abstract

The effects of LH on glucose metabolism within cumulus cell-enclosed bovine oocytes were determined. Cumulus cell-enclosed bovine oocytes were matured in vitro (IVM) in control medium alone or supplemented with LH, FSH, or TSH, then individually assayed for the metabolism of D-[5-3H]glucose, D-[1-14C]glucose, D-[6-14C]glucose, and D-[U-14C]glucose. Glycolytic activity was unchanged after IVM in 1 microgram LH/ml, but was greater (P < 0.05) after culture in 10 and 50 micrograms LH/ml than the control value (1.34 +/- 0.13, 1.87 +/- 0.20, and 1.63 +/- 0.14 vs. 1.19 +/- 0.13 nmol 3H2O/micrograms protein.3 h, respectively). Increased glycolytic activity was observed within cumulus cell-enclosed oocytes, but not in cumulus cell complexes from which the oocyte was removed. Also, no glycolysis was detected when denuded oocytes from any IVM treatment were assayed. Glycolytic activity was greater (P < 0.01) after IVM in LH (10 micrograms/ml) vs. TSH (0.5 microgram/ml), FSH (1.0 micrograms/ml), and control treatments (3.04 +/- 0.10, 2.44 +/- 0.10, 2.33 +/- 0.10, and 2.13 +/- 0.10 nmol 3H2O/micrograms protein.3 h, respectively). Treatment with TSH also increased (P < 0.05) glycolytic activity compared to control values. Relative to control values after IVM, pentose cycle activity was 73.6% less, 2.9% higher, and 33.9% higher with LH, FSH, and TSH treatments, respectively. Total 14CO2 generated from D-[U-14C]glucose did not differ between treatments. Glucose oxidation by the pentose cycle accounted for 30.5%, 29.7%, 40.7%, and 11.1% of the total 14CO2 production after IVM in control medium, FSH, TSH, or LH, respectively. Data indicate that IVM with LH results in increased glycolytic activity and mitochondrial glucose oxidation within cumulus cell-enclosed bovine oocytes, and that this may represent a mechanism by which LH enhances oocyte maturation.