Brain response to protein undernutrition: Mechanism of preferential protein retention

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Abstract

This study was designed to determine how the brain, in contrast to most other tissues, maintains an almost normal protein content during a period of dietary protein deficiency. Administration of leucine-3H to rats was started during a period of early development (6-18 days) which is characterized by disproportionately rapid brain growth; later (24-33 days) leucine-14C was administered, when brain growth diminishes but total body weight gain continues to be rapid. At 35 days of age the ratio of 3H:14C in cerebrum, cerebellum, and brain stem protein averaged between 1.63 and 1.82. In skeletal muscle, liver, myocardium, and intestinal mucosa the mean 3H:14C was 1.07 or less. Then, a diet containing either 26% or 3.4% protein was administered. In animals fed the 26% protein diet, 3H:14C in the three brain segments remained essentially unchanged over a 42 day period. In contrast, in the 3.4% protein group 3H:14C in brain decreased to values approaching those of other tissues in the body: cerebrum, 1.18; cerebellum, 1.20; and brain stem, 1.16. The results suggest that conservation of brain protein is not due entirely to the long life-span of its cellular components or to efficient reutilization of the products of protein catabolism but through utilization of amino acids from degradation of protein elsewhere in the body.

Authors

Peter R. Dallman, Robert A. Spirito