GLUTAMATE OXIDATION BY TROPHOBLASTS IN-VITRO

Catabolism of uniformly and 1(-14)C-labeled glutamate was investigated in human placental cytotrophoblasts and syncytiotrophoblasts cultured on uncoated plastic or a fibrin matrix. Product-labeling experiments resulted in C-14 incorporation into carbon dioxide and tricarboxylic a cid cycle intermediates. C-14 incorporation above background was not d etected for the putative products, glutamine, amino acids, glutathione , and protein. Inhibitors of specific metabolic pathways were used to elucidate the routes of glutamate oxidation. Incorporation of C-14 int o carbon dioxide from [1-C-14]glutamate was inhibited by the glutamate dehydrogenase inhibitor pyridine-2,6-dicarboxylic acid and the aminot ransferase inhibitor aminooxyacetic acid. Production of (CO2)-C-14 was higher for syncytiotrophoblast compared with cytotrophoblast and for cells on uncoated plastic compared with a fibrin matrix. Oxidation of glutamate was unaffected by added glutamine as high as 2 mM. The prima ry route of glutamate metabolism by placental trophoblast in vitro is oxidation to carbon dioxide utilizing both the transferase and deamina tion pathways.