Effect of fructose on the capacity of urea-N synthesis in rats

We studied the effect of fructose on hepatic conversion of amino-N to urea-N as quantified by the Capacity of Urea-N Synthesis (CUNS) determined in rats during alanine loading. There were 2 control groups, one without and one with infusion of somatostatin, in order to control the effects of insulin and glucagon. Somatostatin reduced CUNS from 8.5 +/- 0.5 mumol/(min x 100 g BW) to 6.3 +/- 0.3 mumol/(min x 100 g BW) (mean +/- SEM) (p < 0.01) and reduced glucagon concentrations by 75% (p<0.05). Insulin and glucose concentrations did not change. Fructose, at blood concentrations of about 1 mmol/l further reduced CUNS to 3.6 +/- 0.3 mumol/(min x 100 g BW) (p < 0.01). Insulin increased slightly (p < 0.05), but neither glucose nor glucagon changed. At increasing fructose concentrations up to 2 mmol/l there was no further effect on CUNS. Fructose in concentrations as used for parenteral nutrition and independent of glucoregulatory hormones, decreased hepatic amino acid catabolism.