Increased lactulose/rhamnose ratio during fluid load is caused by increased urinary lactulose excretion

Noninvasive assessment of intestinal permeability in vivo is based on the m easurement of urinary excretion of orally administered sugar probes. It is expressed as a ratio, usually lactulose/ rhamnose or 3-O-methyl-D-glucose ( 3-OMG)/rhamnose. In both endotoxemic and control rats that were receiving f luid, we observed an increase in the recovery of lactulose and 3-OMG but no t rhamnose in both groups, suggesting an enhancement of intestinal permeabi lity. In the measurement of intestinal permeability, all pre- and postmucos al factors are considered equal for all sugars. We hypothesized that postmu cosal factors and not changes in intestinal permeability caused the increas ed urinary lactulose and 3-OMG recoveries observed during fluid loading. Th erefore, the effects of fluid loading on urinary excretion of the sugar pro bes were studied in healthy rats receiving the sugars intravenously. After intravenous injection, fluid loading increased urinary lactulose recovery t hreefold but not that of 3-OMG and rhamnose. In conclusion, fluid loading i ncreases the lactulose/ rhamnose ratio independent of changes in intestinal permeability. The 3-OMG/rhamnose ratio is not influenced by fluid loading.