The Effect of Diet on Lactase Activity in the Rat

Abstract

A study was undertaken to adapt intestinal lactase in weanling rats and to correlate changes in lactase activity with in vivo lactose hydrolysis. The postweaning decline in lactase activity was not prevented by feeding a 10% lactose diet. Lactase activity subsequently rose at 8 weeks of age and remained high for the duration of lactose feeding. A decline in lactase activity occurred after withdrawal of lactose from the diet, and when lactose was reintroduced lactase activity rose. The time taken for these adaptive responses varied between 5 and 10 weeks. Changes in jejunal lactase activity were accompanied by similar alterations in both sucrase and maltase activities, while there was no alteration in another brush border enzyme, alkaline phosphatase. The increase in lactase with a pH optimum of 5.8, with slight alteration of the enzyme with a more acid pH optimum, was taken to be evidence for a brush border location. This was supported by the correlation between increased lactase activity and increased in vivo hydrolysis of 14C-1-lactose in isolated loops of intestine.