REGULATION OF BRUSH-BORDER ENZYME-ACTIVITIES AND ENTEROCYTE MIGRATION RATES IN MOUSE SMALL-INTESTINE

We adapted the Weiser method, previously used to fractionate enterocytes of rat and rabbit intestine, to the much smaller intestine of mice. By histological, morphometric, enzymatic, histochemical, and immunocytochemical evidence, the method succeeded in removing mouse enterocytes sequentially along the crypt-villus axis while preserving cell viability and minimizing mixing among cell fractions. Activities of three brush-border enzymes [alkaline phosphatase (AP), sucrase, and gamma-glutamyl transpeptidase (GGP)] varied simultaneously with dietary substrate level, intestinal region, and position along the crypt-villus axis. All three enzymes proved to be stimulated by dietary substrate: sucrase by dietary sucrose, AP and GGP by dietary protein. We also studied cell migration rates and lifetimes by autoradiography and by our modified Weiser method. By both methods, injected [H-3]thymidine after short times was virtually confined to crypt cells, whereas after 40-48 h it was distributed from the crypt over the whole villus except for the villus tip. Villus height decreased twofold from duodenum to ileum, parallel to the regional decrease in cell migration rates because the cell lifetime of 68 h was independent of region. When we varied dietary carbohydrate and protein levels reciprocally while maintaining protein above the maintenance level, both cell migration rate and cell lifetime proved independent of diet.