Tracer kinetic analysis of Cori cycle activity in the rat: effect of feeding

Turnover rates of blood glucose and lactate, along with the rates of their interconversion, were calculated from changes of their specific activities in rats infused with [U-14C] glucose and [U-14C] lactate based on a simple flux model of the Cori cycle. In the fasted state, most (75%) of the glucose metabolized was converted to lactate, whereas only a small fraction (35%) of the lactate metabolized was converted to glucose. Of the glucose metabolized, 27% returned from the lactate pool to the glucose pool. Feeding stimulated the outflow of glucose carbon from the Cori cycle via the action of secreted insulin. Insulin-induced stimulation of blood glucose removal was associated with increased glucose production, whereas anti-insulin serum-induced stimulation of glucose production was associated with increased glucose removal. It is argued that a "compensatory" mechanism independent of insulin and epinephrine might be in operation to minimize the glycemic changes that would otherwise occur in response to drastic metabolic changes.