Effect of Cold Exposure on the Response of Rats to a Dietary Amino Acid Imbalance

Abstract

Relationships among food intake, growth, liver serine-threonine dehydratase activity (S-TDH) and plasma amino acid concentrations were studied at intervals in cold-exposed rats fed a diet having an amino acid imbalance (5% casein plus 6% amino acid mixture minus histidine). Within 4 hours after rats had eaten a meal of this diet their plasma histidine concentration fell and concentrations of other indispensable amino acids and serine rose; subsequently, food intake and growth were depressed for 2 days. The S-TDH was low initially, rose to a maximum, then fell; but after 9 days was still seven-fold greater than at day zero. As time progressed food intake and growth increased, but plasma histidine concentration remained low while concentrations of other indispensable amino acids remained elevated. The elevated metabolic activity of cold-exposed rats apparently permits them to consume a large quantity of imbalanced diet before their plasma amino acid pattern becomes sufficiently abnormal to elicit a signal leading to curtailment of food intake.