Effect of Krebs cycle metabolites on frog heart

All the Krebs metabolites except pyruvate, lactate, acetate and succinate reduced the force and rate of myocardial contractions and also decreased cardiac output in frog. Succinate on the contrary was found to augment the rate and force of heart. The cardiac stimulation produced by epinephrine was reduced by fumarate, malate, oxaloacetate and alpha-oxoglutarate, whereas transaconitate and citrate produced only a slight inhibition. Pyruvate, lactate, acetate and succinate did not alter cardiac response to epinephrine.