Oxidation of branched chain amino acids by isolated hearts and diaphragms of the rat. The effect of fatty acids, glucose, and pyruvate respiration.

Amino acid oxidation was studied in perfused hearts and incubated hemidiaphragms of rats fed ad Zibitum. Hearts were perfused with Krebs-Henseleit bicarbonate buffer containing glucose and 0.1 mu amino acids. The addition of 1 mM octanoate to the medium markedly stimulated 14COz production from [1-r4C}leucine, isoleucine, and valine; inhibited r4C02 production from [lJ4C]alanine, pyruvate, and oc-ketoglutarate, and did not affect 14C02 production from [r4C]histidine, threonine, glutamate, ornithine, and phenylalanine. Hemidiaphragms incubated with 1 m&r hexanoate or 0.1 to 1.0 mM octanoate increased the oxidation of the branched chain amino acids by SO to 200% and decreased 14C02 production from alanine and pyruvate. Octanoate stimulated the oxidation of isoleucine by hemidiaphragms at isoleucine concentrations between 0.01 to 1.0 mu; when isoleucine exceeded 2 mu, octanoate became inhibitory. Octanoate stimulated the oxidation of the branched chain amino acids in the presence or absence of glucose and in the presence or absence of insulin from the medium, in diaphragms and hearts. Bovine serum albumin did not affect branched chain amino acid oxidation in the absence of added fatty acids; it inhibited the stimulatory effect of the latter. The inhibition was proportional to the albumin concentration. Palmitate and oleate (1 mu) added to albumin (15 mg per ml) stimulated branched chain amino acid oxidation by hemidiaphragms; the effect was smaller than that observed with equimolar octanoate and albumin. In hearts, no effect of 1 mu pahnitate was observed. Butyrate (2 mu) did not affect branched chain amino acid oxidation by hemidiaphragms; 4 mu d2-P-OH butyrate and 4 mu acetate were inhibitory. In hearts and diaphragms, the omission of glucose from the incubation medium stimulated the oxidation of the branched