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Changes in Muscle and Brain Electrolytes in Rats Fed Natural Imbalanced Diets¹

Department of Experimental Nutrition and Food Science, School of Pharmacy and Biochemistry, University of Buenos Aires, Buenos Aires, Argentina

The influence of a natural dietary amino acid imbalance on composition and sodium and potassium content of muscle and brain of weanling rats was studied at 50 and 90 days of age. Muscle water, the distribution of potassium and sodium, and their ratios between the intra- and extracellular space were examined as indications of biochemical maturity. Rats fed an imbalanced diet up to 50 days of age showed changes in muscle, protein, and glycogen similar to those observed previously on the whole carcass, i.e., lower muscle protein and higher muscle glycogen, than in rats fed a balanced low protein diet. No significant differences in the muscle concentration of sodium or potassium were observed; however, there was a close correlation between the individual potassium and nitrogen/water ratio, indicating that muscle potassium content was dependent on the chemical maturity of tissue. Intracellular sodium concentration was higher, and the ratios intracellular potassium/extracellular potassium, extracellular sodium/extracellular potassium, and intracellular potassium/intracellular sodium were lower compared with the group fed the low protein balanced diet; all these differences are statistically significant. Brain potassium was also significantly lower than that in the group fed the balanced diet, especially when expressed as potassium to sodium ratio or potassium per gram of protein nitrogen. Animals fed an imbalanced diet up to 90 days of age showed no differences in composition in absolute values nor in relative proportions when compared with rats fed the balanced diet except for muscle glycogen, which was significantly higher in the rats fed the imbalanced diets. The distribution studies of sodium, potassium, and water showed no differences between the various body compartments of the two sets of animals.

KEY WORDS: • body composition • electrolytes • imbalanced diets

¹ Supported in part by a grant from the Consejo Nacional de Investigaciones Cienttficas y Técnicas (Argentina).

² Member of the Profession of Investigator, Consejo Nacional de Investigaciones Cientificas y Técnicas (Argentina).

Manuscript received 5 July 1973.