Glutamic acid (GA) plasma levels were measured after oral administration of monosodium glutamate (MSG) to laboratory animals, in relation to several variables. Adult mice and rats show similar GA peak plasma levels, area under the curve (AUC) and apparent half-life (T 1 2), while in guinea pigs the values for all these kinetic parameters are higher. Newborn rats and, to a lesser extent, newborn mice show a larger AUC and T 1 2 than the adults, while the opposite was observed in guinea pigs. Within a given animal species the peak level and AUC, but not the T 1 2, increase with the dose of MSG and with the concentration at which the dose is administered. In human volunteers oral administration of MSG (60 mg kg) results in higher plasma peak levels and AUC when MSG is given at 8% as compared to 2% solution. Mouse brain and guinea pig brain GA levels are not affected by oral MSG until the GA plasma level exceeds the basal plasma concentrations by a factor of about 20. These data are utilized to discuss the relevance for man of the neurotoxic effects induced in rodents by MSG.
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