Metabolic interrelations of glucose and lactate in unanesthetized normal and diabetic dogs

Uniformly labelled 14 C-glucose infusions were given to normal and pancreatectomized dogs. Plasma glucose and lactate specific activities were measured by appropriate methods. In normal dogs 14–28% of plasma lactate was found to originate from circulating glucose, and in diabetic dogs 11–18%. This fraction was markedly increased in normal but not significantly so in diabetic dogs during a 2-h infusion of a 6.7–11 mg/kg min glucose load. Uniformly labelled 14 C-L(+)-lactate and glucose-6- 3 H were infused simultaneously for 5 h in normal and pancreatectomized dogs. The glucose turnover rate and incorporation of lactate carbon into glucose were calculated. Of the utilized lactate carbon, 41–49% was incorporated into plasma glucose. The recycling rate of glucose carbon via lactate was estimated to be 3–8% of the glucose turnover rate in the normal dog in the postabsorptive state. The absolute rate of gluconeogenesis from lactate was found to be increased in diabetes.