Water Absorption Enhances the Uptake of Mannitol and Decreases Cr-EDTA/Mannitol Permeability Ratios in Cat Small Intestine In Situ

Background: Recently, we hypothesized that mannitol absorption in human intestinal permeability tests is a reflection of small intestinal water absorption and is dependent mainly on the efficiency of the countercurrent multiplier in the villi. This may affect the outcome of clinical double-sugar permeability tests. We tested the hypothesis in cats, another species with an efficient countercurrent multiplier. Methods: The lumen-to-tissue transport of [ 14 C]mannitol and [ 51 Cr]EDTA was studied in in situ perfused jejunum of eight anaesthetized cats using four isotonic perfusion solutions with varying sodium and glucose content. The transport of water was monitored, and the absorption rate of the probes was calculated by their disappearance from the perfusate. Results: There was a significant positive correlation between water absorption and [ 14 C]mannitol clearance from the different perfusates ( r = 0.99; P < 0.01), whereas this correlation was absent for [ 51 Cr]EDTA clearance ( r = 0.05; P = 0.95). Th...