Monosodium Glutamate Metabolism in the Neonatal Pig: Effect of Load on Plasma, Brain, Muscle and Spinal Fluid Free Amino Acid Levels

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Abstract
Fasted 3-day-old pigs were given by stomach tube 0.01, 0.10 and 1.0 g/kg body weight of monosodium glutamate dissolved either in water or infant formula. At appropriate times plasma, spinal fluid, muscle and brain samples were obtained for amino acid analysis. The levels of glutamate administered included those which could have been ingested by the human infant (0.01 and 0.10 g/kg) and a level ten times greater (1 g/kg). A marked difference in glutamate absorption was noted depending upon the presence or absence of food in the gut. Plasma glutamate levels were elevated maximally 20 minutes after glutamate was administered in water and 90 to 120 minutes after administration in infant formula. Maximum plasma concentrations were essentially the same with both methods of administration. No significant differences in plasma amino acid levels were noted between control animals and those given 0.01 g/kg body weight of glutamate. When glutamate was given at 0.10 g/kg body weight, small elevations in plasma glutamate and aspartate were noted at maximal absorption times. Marked elevations in concentrations of plasma glutamate, aspartate and alanine were noted following a dose of 1 g/kg body weight glutamate. In fasting animals portal plasma glutamate levels were five times greater than peripheral plasma levels. No significant changes in brain, muscle or spinal fluid free amino acid concentrations were noted in animals studied at the 0.01 and 0.10 g/kg body weight level.