Amino acid imbalance and nitrogen retention in adult rats.

Considerable information concerning the effects of amino acid imbalance has accumulated (l-6), and some of the salient features of this phenomenon have been discussed in a recent review (7). Although efforts are being made (8-15) to explain the underlying mechanism, the physiological or metabolic changes associated with the induction of an amino acid imbalance arc still unknown. Recently, Deshpande et al. (I 6, 17), who maintained weanling rats on a low protein diet which contained fibrin, detected decreases in the percentage of absorbed nitrogen retained, in total nitrogen retention, and in food consumption within 24 hours after induction of an amino acid imbalance. It was suggested that the diminished food intake and the rapid decrease in percentage of absorbed nitrogen retained by the weanling rats might be an indication of their reduced ability to utilize the imbalanced diet. Attempts to equalize the food intake by forcibly feeding the imbalanced diet resulted in the death of animals in 2 to 3 days. It was therefore thought that rats trained to eat only during a single short interval each day might be used in order to equalize food intake and to eliminate the possible nonphysiological conditions of forced feeding (18). It was also thought that this procedure should stimulate increased ingestion of the imbalanced diet and thereby magnify the effects observed earlier. The results of such an investigation are includcd in the present report. In addition, the effects of amino acid imbalance on the nitrogen balance of protein-depleted adult rats and adult rats trained to eat for only 2 hours each day have been compared. Both ad libitum and pair-fed control anima.ls were used.