THE INFLUENCE OF CHANGING CELL KINETICS ON FUNCTIONAL DIFFERENTIATION IN THE SMALL INTESTINE OF THE RAT A STUDY OF ENZYMES INVOLVED IN CARBOHYDRATE METABOLISM

The activity of a number of enzymes involved in carbohydrate metabolism was measured in different cellular compartments of the intestinal epithelium by microchemical techniques. The enzyme activities were related to different cell positions along crypt and villus and to cell age. Enzyme activities in proliferating, differentiating and functional cell compartments of the intestine of normal rats were compared with those in which the cell kinetics had been modified. The effect of increased proliferative activity within the crypt of normal animals was studied in the intestine during recovery after low radiation doses. The effect of increased life-span was investigated in germ-free animals. The specific activity of α-glucosidase, present in microvilli, was found to increase considerably during cell differentiation and subsequent cell migration along the villus. Its specific activity remained unchanged in isolated intestinal loops deprived of dissaccharide substrate for 6 weeks. Lactate dehydrogenase and, to a lesser extent, glucose 6-phosphate dehydrogenase show a similar pattern of activity to α-glucosidase. In contrast hexokinase and isocitrate dehydrogenase were equally distributed among crypt and villus cells and no clear differences were observed with increasing cell age. Increased proliferation in the crypts during recovery after low radiation doses resulted in a marked decrease in both crypt and villus cells of activity of α-glucosidase. The germ-free state of the intestine also significantly influences the pattern of α-glucosidase but has little influence on the other enzymes tested.