Time- and dose-dependency of intestinal lactase activity in adult rat on starch intake.

Although it is generally accepted that lactase (beta-D-galactosidase, EC 3.2.1.23) activity is not influenced by intake of saccharides containing alpha-linkages, an effect of these carbohydrates on lactase activity was never thoroughly investigated. Activity of lactase and sucrose alpha-D-glucohydrolase, EC 3.2.1 48) was determined in proximal, middle and distal thirds of the jejunoileum of female, 12-week-old rats, fed for 2 weeks a low-starch (5 cal%), high-fat (73%) diet, and in rats, that after this introduction period were fed for 1, 2 and 3 days, an isocaloric middle-starch (40%), middle-fat (36%) diet or an isocaloric high-starch (70%), low-fat (7%) diet. During the entire experimental period, the body weight changes, food intake and the amount of protein per segment were practically the same in all three dietary groups. In all intestinal segments, increased intake of starch was followed by an increase of lactase and sucroase activity (both expressed as per tissue protein or per intestinal segment ) within the first day. The increase continued during the second day and leveled off during the third day. A highly significant linear correlation was found between the search content of the diets and the lactase activity in all three segments. A highly significant correlation was also established in all three segments between sucrase and lactase activities. These studies thus demonstrated a dose- and time-dependency between the intake of starch (a carbohydrate containing only alpha-linkages) and the activity of lactase, a neutral beta-galactosidase in adult rats.