The effect of epinephrine, glucagon, and the nutritional state on the oxidation of branched chain amino acids and pyruvate by isolated hearts and diaphragms of the rat.

The effect of epinephrine and glucagon on W02 production from C-l-labeled branched chain amino acids, [I-W]pyruvate, [1-Wlalanine, and [U-14Clglucose, was studied in isolated diaphragms and petiused hearts. The tissues were obtained from rats fed ad libitum or fasted for 48 hours. Epinephrine (10m4 M) stimulated *4CO~ production from Ieuciue, valine, and alanine by hemidiaphragms of fasted rats incubated without substrate, but not by hemidiaphragms of rats fed ad libifum. The oxidation of histidine was not atIected by epinephrine. Epinephrine (10m5 to lob6 M) stimulated branched chain amino acid oxidation by hearts of fed or fasted rats during perfusion without substrate. The addition of 5.5 mu glucose to the perfusion medium abolished the stimulatory effect of epinephrine on branched chain amino acid oxidation. The addition of pyruvate markedly inhibited the oxidation of branched chain amino acids by perfused hearts, and abolished the stimulatory effect of epinephrine on this process. Glucagon (2 X 1OV to 5 X lo* M) stimulated branched chain amino acid oxidation by hearts of fasted rats perfused without additional substrate. Insulin added to glucagon caused no further stimulation of leucine oxidation. Glucagon did not stimulate leucine oxidation by hearts of fed rats, nor by hearts of fasted rats perfused with glucose (5.5 mM) or pyruvate (20 mM). Glucagon did not affect branched chain amino acid oxidation by diaphragms. N6, 02’-Dibutyryl adenosine 3’,5’monophosphate (10-Z to 10m3 M) was mildly inhibitory. Hearts and diaphragms of fed rats oxidized pyruvate much faster than those of fasted rats. Epinephrine (10e6 to 10m6 M) stimulated the myocardial oxidation of pyruvate and alanine. Epinephrine (10m4 to 10e5 M) stimulated the uptake and oxidation of pyruvate by diaphragms of fed or fasted rats, but diaphragms of fed rats were more responsive to this effect of epinephrine than those of fasted rats.