C14 studies in carbohydrate metabolism. IV. Characteristics of bicarbonate pool system in the rat

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Abstract
Specific activity curves of expired air were obtained after the injection of NaHC14O3 into normal and alloxan diabetic rats in the postabsorptive and fasted state. The curves were analyzable into three constituent simple exponential functions. This suggested a pool system with three conjoined compartments. The rate of CO2 output being known, pool sizes and rates of carbon movement could be calculated by mathematical treatment of slopes and intercepts. The primary space within which injected C14 equilibrated very rapidly was treated as a single complex pool. Its size was compatible with that of extracellular fluid. Two side-pools were included in the model. The slower moving one had a rate of turnover and size which were greater in the fasted than in the postabsorptive state. This suggests that organic carbon participates in the HCO3– interchange and that CO2 fixation is increased during fasting. No systematic differences between normal and diabetic animals were encountered.