INFLUENCE OF NUTRIENT RESTRICTION AND REALIMENTATION ON PROTEIN AND ENERGY-METABOLISM, ORGAN WEIGHTS, AND MUSCLE STRUCTURE IN GROWING RATS

Male Fischer rats (Charles River, Germany; 79 g initial body weight, n = 24, divided into two groups) were used to determine the effect of p rotein and energy restriction, and subsequent realimentation, on prote in synthesis and degradation in connection with the influence on energ y metabolism and on body composition. Animals of group 1 (controls) we re always fed ad libitum on a stock diet; group 2 (test group) animals were fed a stock diet/cellulose mixture (60/40%) for the first fortni ght (restriction period), and for the second fortnight (realimentation period) the stock diet ad libitum as in group 1. In both periods, the N balance, protein synthesis (end-product method, single dose of N-15 -labelled amino-acid mixture), energy balance (indirect calorimetry), histological muscle-fibre characteristics (EDL muscle), organ weights, and carcass composition were measured. Compared with the controls, te mporary and moderate nutritional restriction by 33% caused significant reductions in daily gain (by 57%), protein synthesis (by 38%), N depo sition (by 50%), and N utilization, diminished the development of the visceral organs and retarded muscle growth (smaller muscle fibres). To tal energy efficiency of restricted rats seemed to be improved. During the following realimentation period, retardation in organ (exception liver) and muscle growth (exception capillaries/fibre) was largely com pensated for by enhanced fat and protein deposition. Both protein synt hesis and degradation increased, but synthesis more than degradation. No differences could be observed in energy efficiency between test and control groups.