Effects of catecholamines on lactic acid output during progressive working contractions

Epinephrine and norepinephrine together (E + NE) and epinephrine (E) alone were infused intravenously in stepwise increasing doses during progressive isotonic tetanic contractions. The goal was to mimic, for in situ dog skeletal muscle, the concentrations of these catecholamines in the blood and the contractions during progressive exercise. The concentrations of lactate and O2 in arterial and muscle venous blood, the arterial plasma concentration of E and NE, PO2 in arterial and muscle venous blood, and the venous outflow were measured. The infusions caused a rise in plasma E and NE like those seen in progressive exercise. Compared with no-infusion controls, the E + NE infusions and the E alone infusion resulted in significant increases in maximal lactic acid output by the muscles during the contractions from 0.24 mumol X g-1 X min-1 in the controls to 0.44 and 0.54 mumol X g-1 X min-1 during E + NE and E alone infusions, respectively. The venous O2 concentrations and partial pressures were not reduced by the infusions. Both infusions resulted in a rise of arterial lactate concentration that could not be accounted for by the lactic acid output of the contracting muscles. The E alone infusions were associated with a rise in maximal O2 uptake during the contractions. Since the effects of the E + NE and E alone infusions were similar, it was suggested that E is more active than NE. It was suggested that E also increased lactic acid production in tissues other than the working muscles.