Decreased expression of glutamate dehydrogenase by prolonged intake of monosodium glutamate in rat brain.

Abstract

One-week-old albino female rats were kept for 1 year in equal groups with or without monosodium glutamate in their drinking water. The concentrations of the glutamate in the brain crude extracts of the monosodium glutamate treated group were twofold higher than those of the control group. There were no significant changes in body weight, brain weight, and protein content, and total RNA and DNA content also did not vary in the two groups of rats. The activities of glutamate dehydrogenase (GDH) were decreased with a 45% reduction in V(max) values in the monosodium glutamate treated group compared to those in the control group, whereas no significant changes were observed in K(m) values between the two groups. The concentration of the enzyme on the Western blot analysis was significantly decreased in the monosodium glutamate treated group, whereas the level of GDH mRNA remained unchanged, suggesting a post-transcriptional control of the expression of GDH or an increased rate of degradation of enzyme protein. These results indicate that the prolonged monosodium glutamate feeding reduces the activity of GDH and subsequently decreases the catabolism of glutamate in rat brain.