MEASUREMENTS OF THE JEJUNAL UNSTIRRED LAYER IN NORMAL SUBJECTS AND PATIENTS WITH CELIAC-DISEASE

Normal intestinal absorption of nutrients requires efficient luminal m ixing to deliver solute to the brush border. Lacking such mixing, the buildup of thick unstirred layers over the mucosa markedly retards abs orption of rapidly transported compounds. Using a technique based on t he kinetics of maltose hydrolysis, we measured the unstirred layer thi ckness of the jejunum of normal subjects and patients with celiac dise ase, as well as that of the normal rat. The jejunum of humans and rats was perfused with varying maltose concentrations, and the apparent Mi chaelis constant (K-m) and maximal velocity (V-max) of maltose hydroly sis were determined from double-reciprocal plots. The true K-m of inte stinal maltase was determined on mucosal biopsies. Unstirred layer thi ckness was calculated from the in vivo V-max and apparent K-m and the in vitro K-m of maltase. The average unstirred layer thickness of 11 c eliac patients (170 mu m) was seven times greater than that of 3 contr ols (25 mu M). The unstirred layer of each celiac exceeded that of the controls. A variety of factors could account for the less efficient l uminal stirring observed in celiacs. Although speculative, villous con tractility could be an important stirring mechanism that would be abse nt in celiacs with villous atrophy. This speculation was supported by the finding of a relatively thick unstirred layer (mean: 106 mu m) in rats, an animal that lacks villous contractility. Because any increase in unstirred layer slows transport of rapidly absorbed compounds, poo r stirring appears to represent a previously unrecognized defect that could contribute to malabsorption in celiac disease and, perhaps, in o ther intestinal disorders.