George J. Klain

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.

Changes in hepatic fatty acid synthesis following glucagon injections in vivo

Summary A marked decrease in hepatic fatty acid synthesis from glucose was observed fifteen and thirty minutes after intravenous injection of glucagon (1mg/kg) in anesthetized rats. This effect was apparently brought about by an inhibition of acetyl CoA carboxylase activity. Activities of fatty acid synthetase, citrate cleavage enzyme, NADP-malic-, glucose-6-phosphate-, and isocitric dehydrogenase were not affected by glucagon.

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)

Metabolic Studies of an Amino Acid Imbalance in Cold-exposed Rats

Abstract : Young rats fed an amino acid-imbalanced diet based on 6% fibrin, and supplemented with 0.4% DL-methionine and 0.6% DL-phenylalanine had increased activities of liver arginine synthetase and arginase, and increased plasma levels of a number of amino acids. However, the activities and levels of these metabolites were decreased in a comparable group of animals exposed to 7 C. The activity of the expired CO2, originating from intraperitoneally administered 2 microcuries each of carbon labeled methionine, phenylalanine or alanine, indicated that the rats kept at room temperature could not effectively oxidize the two imbalancing amino acids to maintain a proper balance in the amino acid pool for the protein synthesis. In contrast, the cold-exposed animals were able to catabolize the excessive levels of methionine and phenylalanine and utilize them for energy purposes. The remaining balanced portion of the amino acid pool was then apparently used for the formation of new tissues, as also indicated by greater gains in body weight. In another experiment it was shown that proteindepleted rats exposed to 3 C for 27 hours readily consumed the imbalanced diet, while the food intake of a comparable group of rats kept at 25 C fell off sharply 18 hours after the animals had been given the diets. (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.

Sequential changes in alanine metabolism following partial hepatectomy in the rat.

After partial hepatectomy, the liver undergoes an array of metabolic changes until regeneration is complete. Since carbons derived from alanine can be incorporated into most metabolic pools, we studied the metabolism of (14)C-labeled alanine during the early phase of regeneration. Sham operated (controls) and partially hepatectomized rats weighing about 200 g each were injected intraperitoneally with 1-[U-(14)C]alanine at 9, 18, and 36 hours after surgery. The animals were killed 2 hours after injection. Compared to the controls, alanine oxidation was markedly depressed (P < 0.05) in the 9- and 18-hour groups, but was restored in the 36-hour group. The specific activity of plasma glucose and hepatic glycogen was elevated 9 and 18 hours after partial hepatectomy. There was a corresponding increase in the activities of fructose-1,6-diphosphatase and phosphoenolpyruvate carboxykinase. Hepatic protein specific activity increased by 30, 74, and 120%, respectively 9, 18, and 36 hours after partial hepatectomy. Hepatic fatty acids followed a similar pattern. In a separate set of experiments, the distribution of radioactivity in glutamic acid was measured. The results showed that alanine carbons enter the citric acid cycle primarily via the acetyl CoA pathway in the controls, but via the oxaloacetate pathway in partially hepatectomized rats. The results demonstrate significant changes in the activities of metabolic pathways of alanine in the early phase of hepatic regeneration.