Increased glutamine metabolism in bovine cumulus cell-enclosed and denuded oocytes after in vitro maturation with luteinizing hormone.

Abstract

The effects of LH on tricarboxylic acid (TCA) cycle activity within denuded and cumulus cell-enclosed bovine oocytes were investigated by measuring the metabolism of L-[14C(U)]glutamine and [2-14C]pyruvate to 14CO2 after in vitro maturation (IVM) with LH in serum-free, defined culture conditions. Initially, intact cumulus cell-enclosed oocytes or oocytectomized cumulus cell complexes were incubated for 24 h for IVM in control medium alone or supplemented with LH (10 micrograms/ml) before assessment of glutamine metabolism. Glutamine oxidation was increased (p < 0.01) only after IVM of intact cumulus cell-enclosed oocytes with LH when compared to either intact untreated controls, untreated oocytectomized controls, or oocytectomized cumulus cell complexes after LH treatment (0.23 +/- 0.02 vs. 0.13 +/- 0.01, 0.12 +/- 0.01, and 0.12 +/- 0.01 nmol 14CO2/micrograms protein/3 h, respectively). Glutamine metabolism was greater (p < 0.001) in denuded oocytes from cumulus cell complexes that were exposed to LH during IVM versus nontreated controls (6.4 +/- 0.3 vs. 5.1 +/- 0.2 pmol 14CO2/oocyte/3 h, respectively). Glutamine metabolism was increased (p < 0.05) in cumulus cell-enclosed oocytes after LH exposure during IVM but was unchanged after exposure to either FSH or thyroid-stimulating hormone when compared to control treatments (0.23 +/- 0.01, 0.20 +/- 0.02, 0.19 +/- 0.01 vs. 0.16 +/- 0.02 nmol 14CO2/micrograms protein/3 h, respectively). Pyruvate metabolism was not different between LH and control treatments. Evidence demonstrated that LH acts via the cumulus cells to increase glutamine metabolism within intact cumulus cell-enclosed oocytes and in mature oocytes denuded after LH exposure.(ABSTRACT TRUNCATED AT 250 WORDS)