Studies on Myocardial Metabolism : On Amino Acid Metabolism

Abstract

Since it was made possible by the technique of coronary sinus catheterization to study the myocardial metabolism under physiological conditions, a number of investigation using this technique have been made and they clarified that glucose, pyruvate, lactate, acetate and fatty acids may serve as fuel for energy production in the heart. Little work, however, has been published on the myocardial metabolism of amino acids. In 1954, Bing, studying the utilization of amino acids in the human heart by the method of coronary sinus catheterization, concluded that the human heart can utilize considerable quantities of amino acids, and during infusion of amino acids (Aminosol) the rise in arterial amino acid concentration produced a disproportionate increase in the myocardial extraction. However, he studied principally the myocardial extraction of total amino acid nitrogen, without pursuing in parallel observations the behavior of individual amino acids.In the present paper, studies have been made on the myocardial amino acid metabolism with special regard to amino acid fractions in normal as well as liver-impaired dogs, using the coronary sinus catheterization. Furthermore, observations have been carried out on the effects of infusion of amino acid preparations (glutamic acid, alanine, and Moriamin S) on the changes in the metabolism of amino acids.Methods : Simultaneous blood samples were drawn from the coronary sinus and femoral artery for analysis. Coronary venous blood was obtained by means of direct catheterization of the coronary sinus. Total blood amino acid nitrogen was measured according to the procedure of Albanase and Irby, and individual plasma amino acid fractions, to the method of high valtage paper electrophoresis. Blood glucose, pyruvate and lactate were determined, respectively, by methods of Somogyi and Nelson, Freedmann and Haugen, and Barker and Summerson. The manometric method of Van Slyke and Neil was used for blood gas (O2, CO2) analysis. The coronary arteriovenous differences of total amino acid nitrogen, individual amino acid, carbohydrates and blood gases were estimated in normal dogs. Some of these dogs were orally administered with carbon tetrachloride, 1 cc per kg and they were catheterized again in from five to seven days to study the myocardial amino acid metabolism during the liver injury. In addition, for the purpose of studying the effects of amino acid preparation on the cardiac metabolism, 3.3% glutamic acid and 3.3% alaninc solution, and mixed amino acids-preparation (Moriamin S) were respectively infused intravenously at a rate of 50-60 drops per minute to them and samples were drawn five minutes after the onset of, and thirty minutes following the cessation of the infusion.Results : 1) In about a half of 200 normal cases the coronary arterio-venous differences of total amino acid nitrogen were negative; viz. 88 cases negative, 82 cases positive and 30 cases almost zero. It seemed unlikely that there was such a definite extraction of amino acid nitrogen as reported by Bing. (Fig. 2)Concerning the individual amino acid fractions, A1 (Glu), A2 (Asp) and B1 (Arg) showed a tendency to be excreted, and N5 (Ala) and N4 (Val, Leu, Ileu), to be extracted. (Fig. 3)2) With the administration of 3.3% glutamic acid solution to normal dogs, the coronary blood concentration of total amino acid nitrogen was increased markedly, and its coronary A-V difference slightly. As to amino acid fractions, the extraction of A1 (Glu) was increased, and, on the contrary, N5 (Ala), B1 (Arg) and N4 (Val, Leu, Ileu) showed a tendency to be excreted. There was inconsistent behaivar cancerning the carbohydrate metabolism. The myocardial O2 extraction increased and the cardiac respiratory quotient depressed. (Fig. 4, 5)3) With the administration of 3. [the rest omitted]