Effect of physiologic concentration of lactose on prevention of postweaning decline of intestinal lactase

Postweaning decline of intestinal lactase activity due to decreasing substrate concentration was investigated in this study, using litters of rats maintained on either a control (8% dextrose) or lactose-enriched diet (8% lactose). The 8% lactose was used because this supplies the same amount of calories as the lactose in the maternal milk of rats. The rats were sacrificed at 3, 4, 5, 8, 12 and 16 weeks, to establish a continuum of activity. Assay of lactase activity in mucosa from the jejunal and ileal segment in these rats failed to reveal any significant difference in either lactase, sucrase or maltase activity, regardless of whether the activities were expressed in terms of the whole intestine, per gram of intestine, or per 100 g of body weight. These results do not support the theory that postweaning decline of intestinal lactase reflects only a decreasing amount of substrate in the diet.