Effect of alanine concentration independent of changes in insulin and glucagon on alanine and glucose homeostasis in the conscious dog

The effect of an alanine load per se on hepatic alanine balance and hepatic glucose production is unclear. To examine this question, alanine was infused into six postabsorptive dogs at a rate of 6 μmol/kg-min, while maintaining insulin and glucagon levels using the pancreatic clamp technique. The arterial alanine concentration rose from a basal level of 227 ± 16 μmol/L to 497 ± 40 μmol/L during alanine infusion (P < .01). The net hepatic fractional extraction of alanine remained unchanged, while hepatic alanine uptake increased from 3.0 ± 0.3 to 6.0 ± 0.4 μmol/kg-min (P < .01). Conversion of alanine into glucose increased 87% to 2.7 ± 0.3 μmol/kg-min during alanine infusion (P < .01) while gluconeogenic efficiency remained essentially unchanged. Despite the increased gluconeogenic rate, the total rate of glucose production was unchanged. These data suggest that an increase in the alanine load to the liver causes a proportional increase in net hepatic alanine uptake and the gluconeogenic rate, but that in an overnight fasted animal this increase is insufficient to significantly increase glucose production.