Effect of abomasal glucose infusion on alanine metabolism and urea production in sheep.

The effect of abomasal infusion of glucose (120 kJ/d per kg body weight (BW)0.75, 758 mmol/d) on urea production, plasma alanine-N flux rate and the conversion of alanine-N to urea was studied in sheep offered a low-N diet at limited energy intake (500 kJ/d per kg BW0.75), based on hay and grass pellets. Glucose provision reduced urinary N (P = 0.040) and urea (P = 0.009) elimination but this was offset by poorer N digestibility. Urea-N production was significantly reduced (822 v. 619 mmol/d, P = 0.024) by glucose while plasma alanine-N flux rate was elevated (295 v. 342 mmol/d, P = 0.011). The quantity of urea-N derived from alanine tended to be decreased by glucose (127 v. 95 mmol/d) but the fraction of urea production from alanine was unaltered (15%). Plasma urea and alanine concentrations (plus those of the branched chain amino acids) decreased in response to exogenous glucose, an effect probably related to enhanced anabolic usage of amino acids and lowered urea production.