The effect of a low-protein diet, and of refeeding, on the composition of liver and muscle in the weanling rat

ABSTRACT

(1) Fifty-six weanling rats were fed on a low-protein, high-carbohydrate diet designed to simulate that eaten by poor people in Jamaica. After 4 weeks one group was killed and the remainder were rehabilitated on a stock diet containing 18 percent protein. (2) Measurements were made of the protein and deoxyribonucleic-acid content of liver and muscle at the end of the depletion period, at various times during recovery, and also in control animals growing normally. (3) The 'Jamaican' diet caused a virtually complete arrest of growth. Body-weight, liver weight and muscle weight remained constant at the levels reached on weaning. The ratio of nitrogen to DNA was greatly reduced in both liver and muscle. In muscle this reduction occurred entirely at the expense of cellular protein. The connective tissue of muscle continued to increase in amount throughout the depletion period. (4) On refeeding there was a rapid formation of new protein and DNA in the liver, at about twice the rate that obtains during normal growth. In muscle, on the other hand, there was evidence of a lag period before the synthesis of new tissue reached its maximum rate. (5) The bearing of these results on the assessment and treatment of protein malnutrition in human infants is discussed. They tend to support the suggestion previously put forward, that the ratio of non-collagen nitrogen to DNA in muscle may be a useful index of the degree of protein depletion (AU)