Glucose Uptake by Isolated Perfused Hearts from Fed and Fasted Rats.

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Abstract
Summary Glucose uptake and lactate production have been measured in isolated perfused rat hearts from ad libitum-fed and overnight fasted rats. At perfusate glucose levels of 75, 150 and 300 mg% (62.5, 125 and 250 μmoles glucose/perfusate, respectively), hearts from fed animals removed glucose at higher rates; however, by 30 minutes, glucose uptake in fed and fasted hearts was the same when perfused with 300 mg% glucose. These data were reproducible and in all cases uptake conformed to first order kinetics. Lactate production by hearts from fasted rats exceeded that from “fed” hearts, indicating higher rates of glycolysis. However, glucose oxidation to C14O2 by “fed” or “fasted” hearts perfused with 150 mg% glucose-U-C14 for 30 minutes were similar. These results are discussed in relation to rate of C14O2 production, time of perfusion, and utilization of metabolically-produced lactate. Differences in glucose uptake and lactate production between hearts from fed and fasted rats could not be related to differences in levels of glucose-6-phosphate dehydrogenase, malic dehydrogenase (NAD), lactic dehydrogenase, or fructose-1,6-diphosphate aldolase. Also, perfusion of hearts with 300 mg% glucose did not significantly increase these enzyme levels.