David A. Vaughan

Interrelationships of Cold Exposure and Amino Acid Imbalances

Abstract : A moderate cold exposure has been used as a tool in inducing a higher food intake in experiments dealing with amino acid imbalances in the rat. The data indicate that the rats kept at 25 C suffer a severe metabolic disorder after ingesting amino-acid-imbalanced diets. In contrast, the animals kept at 7 C readily consumed the imbalanced diets and, consequently, grew as well as the controls. The activity of the glutamic oxalacetic and the glutamic-pyruvic transaminase were found to be increased as a result of cold exposure. It is suggested that a moderate cold stress is an effective agent in correcting and overcoming amino acid imbalances.

Some Metabolic Effects of Methionine Toxicity in the Rat

Abstract : Rats consuming a 15% casein diet containing 4.0% of DL methionine developed the following metabolic alterations in the liver: increased activities of arginase, tryptophan pyrrolase, glutamic-oxalacetic and pyruvic transaminase, decreased levels of DPN and slightly increased levels of total and neutral fat. However, the fat content approached a normal level at the end of the tenth week of the experimental period. Urinary excretion of a number of amino acids was also markedly increased. Supplementation of the high methionine diet with 4.0% of glycine decreased the activity of arginase and the levels of some amino acids in the urine. The data indicate that ingestion of excess methionine leads to a disorder in nitrogen metabolism, and that the supplemented glycine diminishes these catabolic processes. (Author)

Effect of protein intake and cold exposure on selected liver enzymes associated with amino acid metabolism.

Abstract : The activity of five liver enzymes involved in amino acid metabolism was found to be markedly increased in cold-exposed rats. However, the activity of three of the enzymes, arginase, glutamic-oxalacetic and glutamic-pyruvic trans aminase, was incresed only as a result of a cold-induced higher protein intake. In contrast, the activity of tryptophan pyrrolase and tyrosine alpha ketoglutaric transminase was increased by cold per se. The data demonstrate that both sub strate-induced and cold-induced enzymatic changes occur in cold- exposed animals.

Excretion of tritium-labeled pyridoxine by pyridoxine-deficient rats*

The excretion of injected doses of tritium-labeled pyridoxine was measured in rats made deficient by deprivation of the vitamin compared with rats made deficient by administering the antagonist, desoxypyridoxine. The results support the hypothesis that desoxypyridoxine blocks some of the available sites for attachment of pyridoxine phosphate.

Dietary modifications of cold-induced metabolic effects☆

Abstract Cold-exposed male Sprague-Dawley rats were forced to obtain their extra caloric requirements from either carbohydrate (sucrose) or fat (Crisco). Rats were killed 1, 4, and 8 weeks after initiation of the feeding regimen. Carcass fat, protein, and moisture analyses were made. Liver glucose-6-phosphatase, HMP dehydrogenase, and glycogen were assayed. At the end of 4 and 8 weeks the percentages of fat in the carcasses of these rats were significantly higher than in the cold rats receiving a mixed complete diet ad libitum. The 2 enzymes studied showed differing responses, HMP dehydrogenase increasing as a result of higher input of carbohydrate in the cold, and G-6-Pase increasing as an apparent result of cold exposure per se.

Effects of hypoxia and dietary aspirin on plasma and urinary amino acids in the rat

Abstract Plasma and urinary free amino acids were studied in rats receiving 0.5 percent acetylsalicylic acid (aspirin) while exposed to simulated high altitude. Rats were placed in a chamber at simulated 17,500 feet for 2 weeks. They were then fed a casein-based diet containing 0.5 percent aspirin as meals of 2 hour duration for a period of 2 weeks. Altitude and diet controls were run simultaneously. Plasma concentrations of 15 amino acids were measured at intervals of 4, 8, 15, and 22 hours after the last meal. Both aspirin and altitude modified the post prandial pattern of these amino acids. Glutamic acid levels rose sharply in the aspirin fed rats at both ground level and altitude. Dietary controls showed no such rise. Both aspirin feeding and altitude exposure depressed peak concentrations of the other amino acids independently and there were no interactions between the two treatments. Aminoaciduria did not occur in either the aspirin-fed or altitude exposed rats. Although changes in renal function cannot be entirely ruled out, it would appear that both aspirin and altitude may affect amino acid absorption and metabolism and that these effects are often additive.