Effects of ageing on the oral absorption of D-xylose in rats.

The effects of ageing on the oral absorption of D-xylose were investigated in rats. The pharmacokinetic analysis of D-xylose concentration in plasma after oral administration showed that the fraction absorbed was increased to 0.998 +/- 0.002 and 0.950 +/- 0.049, respectively, in old (52 weeks) and very old (102 weeks) rats, compared with 0.768 +/- 0.052 in young (9 weeks) rats, while the absorption rate constant was not significantly changed: 0.944 +/- 0.233, 0.844 +/- 0.143 and 0.725 +/- 0.004 h-1, respectively, in young, old and very old rats. The absorbed fractions estimated from faecal and urinary excretion were in agreement with those by the pharmacokinetic analysis. Thus, the present study demonstrated an increase in the extent of the oral absorption of D-xylose with ageing. The increase in the extent of absorption might be caused by a delay in the intestinal transit, because the absorption rate constant was unchanged. These results suggest potential increases with ageing in the fractions absorbed of hydrophilic drugs such as D-xylose where oral absorption is incomplete.