title: Effects of xylitol versus glucose on urea synthesis and alanine metabolism in rats.
abstract: The relation between xylitol concentration (1.0 and 5.5 mmol/1), the Capacity of Urea-N Synthesis, and the rate of Alanine Metabolism was investigated in nephrectomized rats of 200 g and compared with the effect of glucose at concentrations between 5.5 and 15.5 mmol/1. The xylitol and glucose concentrations were controlled by "clamp" techniques and the endogenous hormonal effects by somatostatin. The Capacity of Urea-N Synthesis was determined during alanine infusion to constant amino acid concentrations within the interval 7.3-11.6 mmol/1. The rate of alanine metabolism was assessed as alanine infusion rate corrected for changes in alanine concentration. At normal hormonal response, xylitol at 1.0 mmol/1 and 5.5 mmol/1 reduced urea synthesis from 10.3 +/- 1.1 mumol/(min.100 g) in controls to on average 6.2 +/- 0.9 mumol/(min.100 g) (mean +/- SD, n = 2 x 10, p < 1.01). Alanine metabolism was reduced to the same extent. Glucose concentration increased from 5.4 +/- 1.0 mmol/1 in controls to 8.1 +/- 1.4 mmol/1 at both xylitol concentrations. Xylitol reduced plasma glucagon concentration to one third and tripled plasma insulin concentration. During somatostatin and blood glucose maintained above 8 mmol/1, the Capacity of Urea-N Synthesis fell to 6.1 +/- 1.0 mumol/(min.100 g). In that situation, xylitol at 1.0 mmol/1 reduced neither urea synthesis nor alanine metabolism, whereas xylitol at 5.5 mmol/1 further reduced urea synthesis to 3.4 +/- mumol/(min.100 g) (n = 10, p < 0.05) and almost stopped alanine metabolism. Thus xylitol, independently of glucose and hormonal responses, inhibited urea synthesis and alanine metabolism. This may have therapeutic implications at catabolic conditions.
authors.affiliation: Division of Hepatology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: B A
authors.initials: BA
authors.lastname: Hansen
authors.forename: T P
authors.initials: TP
authors.lastname: Almdal
authors.forename: H
authors.initials: H
authors.lastname: Vilstrup