Effect of Prolonged Nursing on the Activity of Intestinal Lactase in Rats

Litters of 10-day-old rats and their mothers were placed in specially designed cages which enabled the pups to continue to suckle, not to have access to water, solid foods, or feces, and to ensure that their sole dietary carbohydrate was lactose. The animals were killed at intervals and intestinal β-galactosidases, α-glucosidases, and cellular proliferation were measured. Although the specific activity of intestinal lactase followed the usual decline observed during development, the enzyme was maintained at a significantly higher activity than that of control rats. These animals were also able to hydrolyze lactose more readily as demonstrated by their having a significantly higher concentration of glucose in blood after ingestion of lactose. When segments of intestine were incubated with lactose, glucose plus galactose, sucrose, mannitol, or saline, the decline in the activity of lactase was much less in the presence of lactose than in any of the other media. Thus, the substrate had a stabilizing or protective effect on the enzyme. The developmental pattern of the intestinal a-glucosidases and the "acid" β-galactosidases, and the normal morphological maturation of the intestine were not altered by prolonged nursing and elimination of carbohydrates other than lactose.