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Plasma Tryptophan Levels and Brain Serotonin Metabolism in Chronically Uremic Rats^1,2,

Schools of Public Health and Medicine, University of California, and Medical and Research Services, Veterans Administration, Wadsworth Hospital Center, Los Angeles, California 90024

Plasma tryptophan (Trp) levels and brain concentrations of Trp, serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) were measured in chronically uremic rats fed either 11% or 18% casein diets for 8 to 12 weeks. Uremic rats had increased levels of plasma urea nitrogen and 5-HIAA when compared with sham-operated pair-fed controls. The level of plasma total Trp decreased in both uremic groups and the level of plasma free Trp increased only in those fed an 11% casein diet. Uremic rats fed 11% casein had a higher level of plasma free Trp than those fed 18% casein. The ratio of plasma total Trp to the sum of five amino acids competing for the blood-brain transport system was decreased in both uremic groups, and the ratio of plasma free Trp to the same amino acids was increased only in uremic rats fed 11% casein. The concentration of brain 5-HIAA increased in uremic rats fed 11% casein, and that of Trp and serotonin decreased in uremic rats fed 18% casein. These results indicate that uremic stress and changes in protein intake in chronic uremia alter plasma Trp levels and brain serotonin metabolism.

KEY WORDS: • uremia • tryptophan • serotonin • 5-hydroxyindoleacetic acid

¹ Supported in part by Public Health Service Grant No. AM 15197.

² The data are taken from a Ph.D. dissertation by the senior author.

³ Present address: Department of Human Ecology, School of Health & Institute of Public Health Research, University of Teheran, P.O. Box 1310, Teheran, Iran.

⁴ Present address: Department of Foods and Nutrition, School of Home Economics, University of Georgia, Athen, Georgia 30602.

Manuscript received 16 August 1976.