Effect of alanine infusion on glucose and urea production in man

We have tested the response to a primed constant infusion of alanine (2 mg/kg X min infusion, 120 mg/kg prime) on glucose and urea kinetics in overnight fasted volunteers by using primed-constant infusions of 6,6-d2-glucose and 15N2-urea. When no alanine was infused, plateaus in glucose and urea concentration and enrichment were maintained for the final 3 hr of a 4-hr infusion of tracers. When alanine was infused over the final 2 hr of a second protocol, urea enrichment decreased significantly, indicating an increase in urea production from 4.4 +/- 0.31 to 7.0 +/- 0.63 mumol/kg X min. This corresponded to a potential increase in gluconeogenesis from alanine of 20%. Nonetheless, the alanine infusion had no significant effect on either the plasma concentration or enrichment of glucose, which means that hepatic glucose output was not affected. We conclude, therefore, that increasing gluconeogenic precursor availability does not stimulate hepatic glucose output in overnight-fasted man.