Abstract

The objective of the present study was to define the parameters under which the anaerobic turtle heart utilized exogenous glucose as a substrate to maintain cardiac contractility under control working conditions and when pharmacologic cardiac stimulants such as epinephrine were administered. The temporal relationship of glucose uptake and lactate production was studied in the presence and absence of 5 x 10^-8 M epinephrine. The data indicated that glucose was utilized by the heart muscle under conditions of low work load, and the presence of epinephrine caused a further and significant increase in glucose uptake. Epinephrine alone did not stimulate lactate production although its characteristic inotropic effects were seen. The presence of glucose in the perfusion medium increased the rate of lactate formation in the presence and absence of epinephrine. Glucose also appeared to antagonize the glycogenolytic response of the heart tissue to epinephrine and sustained the duration of the epinephrine-induced inotropic response. Glucose alone produced a positive inotropic response very similar to that induced by epinephrine.