[Frontiers in Bioscience E3, 279-290, January 1, 2011]

Effects of monosodium glutamate supplementation on glutamine metabolism in adult rats

Claire Boutry1,2, Cecile Bos1,2, Hideki Matsumoto3, Patrick Even1,2, Dalila Azzout-Marniche1,2, Daniel Tome1,2 and Francois Blachier1,2

1 INRA, CNRH-IdF, UMR 914 Nutrition Physiology and Ingestive Behavior, F-75005 Paris, France, 2AgroParisTech, CNRH-IdF, UMR 914 Nutrition Physiology and Ingestive Behavior, F-75005 Paris, France, 3AJINOMOTO Company, Institute of Life Sciences, Amino Acid Basic and Applied Research Group, Ajinomoto Co., Inc, Kawasaki 210-8681, Japan

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Materials and methods
3.1. Animals and diets
3.2. Experimental protocol
3.3. Determination of protein synthesis rate in tissues
3.4. Determination of oro-fecal transit time and gastric emptying rate
3.5. Determination of glutaminase and glutamine synthetase activity in tissues
3.6. Measurement of gene expression of glutaminase and glutamine synthetase activity
3.7. Protease activity and peptide contents
3.8. Assessment of the postprandial kinetics of dietary N
3.9. Hormones, glucose and amino acid concentrations
3.10. Statistics
4. Results
4.1. Food intake, body weight and body composition
4.2. Gastro-intestinal transit and luminal intestinal proteases activity
4.3. Amino acid and enzymes related to glutamine metabolism
4.4. Dietary and whole body protein metabolism
4.5. Glucose and insulin
5. Discussion
6. Acknowledgment
7. References

1. ABSTRACT

Monosodium glutamate (MSG) is a worldwide used flavor enhancer. Supplemental glutamate may impact physiological functions. The aim of this study was to document the metabolic and physiological consequences of supplementation with 2% MSG (w/w) in rats. After 15 days-supplementation and following the ingestion of a test meal containing 2% MSG, glutamic acid accumulated for 5h in the stomach and for 1h in the small intestine. This coincided with a significant decrease of intestinal glutaminase activity, a marked specific increase in plasma glutamine concentration and a transient increase of plasma insulin concentration. MSG after chronic or acute supplementation had no effect on food intake, body weight, adipose tissue masses, gastric emptying rate, incorporation of dietary nitrogen in gastrointestinal and other tissues, and protein synthesis in intestinal mucosa, liver and muscles. The only significant effects of chronic supplementation were a slightly diminished gastrocnemius muscle mass, increased protein mass in intestinal mucosa and decreased protein synthesis in stomach. It is concluded that MSG chronic supplementation promotes glutamine synthesis in the body but has little effect on the physiological functions examined.