Effects of pre- and post-absorptive factors on the lactulose/rhamnose gut permeability test

It is assumed that the outcome of the lactulose/rhamnose gut permeability t est is not influenced by pre- or post-absorptive factors. The aim of our st udy was to investigate the role of a preabsorptive factor, i.e, small-intes tinal transit, and a post-absorptive factor, i.e. renal clearance. Ten heal thy male subjects were studied. Urinary lactulose and rhamnose excretion wa s measured after intraduodenal administration of lactulose and rhamnose fol lowing induction of increased intestinal permeability using chenodeoxycholi c acid (chenodiol), in the absence and in the presence of accelerated intes tinal transit. Urinary sugar excretion was measured after intravenous admin istration of either a regular dose (50 mg/50 mg) or a high dose (250 mg/250 mg) of lactulose/rhamnose. The intraduodenal experiments showed that a com bination of accelerated small-bowel transit and increased permeability did not lead to significant differences in the recovery of lactulose (P = 0.647 ) or rhamnose (P = 0.889), or in the lactulose/rhamnose ratio, compared wit h those under conditions of increased permeability alone (P = 0.68). Howeve r, lactulose recovery was significantly lower (P = 0.025) after intravenous administration of a high dose of the sugars. There was no significant diff erence in urinary rhamnose recovery (P = 0.575) between the high and the re gular doses. This resulted in a significantly lower lactulose/rhamnose rati o (P = 0.021) after intravenous administration of a high dose, compared wit h a regular dose, of the sugars. In conclusion, the assumption that post-ab sorptive processes do not influence the outcome of the lactulose/rhamnose p ermeability test appears not to be valid.