Effect of carbohydrate on plasma and erythrocyte glutamate levels in humans ingesting large doses of monosodium L-glutamate in water.

In previous studies, plasma glutamate concentration was lower when equivalent doses of monosodium L-glutamate (MSG) were given with a ready-to-feed liquid formula meal (Sustagen; 0.4 g protein, 1.1 g carbohydrate, 0.06 g fat, 6.6 kcal energy/kg body weight) rather than in water. This difference was suggested to reflect a carbohydrate effect on mucosal cell glutamate metabolism. To test this hypothesis, a large dose of monosodium L-glutamate (150 mg/kg body weight) dissolved in water, with or without added carbohydrate, was administered to eight healthy adult subjects. Carbohydrate was administered at 1.1 g/kg body weight in the form of partially hydrolyzed corn starch (Polycose). In the absence of carbohydrate, the mean (+/- SD) peak plasma glutamate concentration was 59.4 +/- 46.5 mumol/dl, and the incremental area under the plasma glutamate concentration time curve was 3391 +/- 2360 mumol/(dl x min). The addition of carbohydrate to the glutamate solution significantly decreased (p = 0.001) both the mean peak plasma glutamate concentration (7.18 +/- 3.48 mumol/dl) and the incremental area under the plasma glutamate concentration-time-curve (451 +/- 20.8 mumol/(dl x min). Erythrocyte glutamate and aspartate concentrations were not affected by glutamate loading in either test. Delayed gastric emptying did not account for the carbohydrate effect. Carbohydrate is postulated to serve as a pyruvate source for mucosal cells, facilitating the transamination of glutamate and its subsequent metabolism. This process would reduce the release of glutamate to the peripheral circulation.