Plasma and brain levels of glutamate and pyroglutamate after oral monosodium glutamate to rats.

Plasma and brain levels of pyroglutamate (Py), a compound connected with the pathway of glutamate (GA) metabolism, were measured in rats after oral administration of monosodium glutamate (MSG) or Py. Oral MSG (1 g/kg) was followed by only a small rise in plasma Py levels. No increase of Py or GA brain levels was observed in these experimental conditions. Oral administration of Py (0.05, 0.5 and 1 g/kg) resulted in a marked dose-dependent increase of plasma Py, but no increase of plasma or brain GA levels. However, Py accumulated in brain in a dose-related manner. After 0.05 mg/kg the basal brain levels remained unchanged at all the times considered. Rat brain Py levels significantly increased when the oral dose of Py was raised to 0.5 g/kg. Peak brain levels were reached at 240 min, and were about 3 and 4 times the basal levels after 0.5 and 1 g/kg, respectively.