Demonstration of a difference in expression of maximal lactase and sucrase activity along the villus in the adult rat jejunum.

Lactase and sucrase are two disaccharidases that differ not only in their substrate specificity and developmental patterns, but also in their resistance to mucosal insult. In this experiment, we tested the hypothesis that there might be a dichotomy in expression of enzyme activity along the jejunal villuscrypt unit. Sectioning of the villus-crypt unit in a cryostat enabled direct comparison of the distribution of lactase and sucrase enzyme activities in the adult rat. There is a stepwise increase in mean lactase/sucrase ratio going from crypt to villus. The data indicate that unlike sucrase activity, which is expressed maximally in enterocytes along the entire villus, maximal lactase activity is not attained until midvillus. The delay in expression of maximal lactase activity might help to explain the vulnerability of this enzyme to acute mucosal insult such as occurs in viral gastroenteritis.