Regulation of glucose oxidation in the white rat

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Abstract
The rate of oxidation of glucose has been measured in 43 rats acclimated to 30 C, at rates of turnover of 8–105 mg glucose carbon/100 g body wt. per hour (mg C/100 g·hr) by the technique of priming and continuous infusion of trace amounts of C14-glucose. This range of glucose turnover values had been obtained by using rats in various nutritive states or by continuous infusion of nonlabeled glucose. Oxidation was directly proportional to turnover between rates of turnover of 8 and 40 mg C/100 g·hr with a slope of about 0.5. At higher rates of turnover the ratio of oxidation to turnover decreased to 0.35, thus indicating that oxidation was approaching a maximum. At the highest rates of glucose turnover, a maximum of 63% of the respiratory CO2 was derived from body glucose, although the amount of non-labeled glucose carbon injected per minute exceeded the respiratory CO2 carbon by a factor of 1.8. Therefore, oxidation of glucose in the intact rat is closely regulated by its availability, but body glucose does not appear to serve as sole substrate for respiration even when its rate of turnover exceeds the respiratory output of carbon.