Intestinal brush border membrane structure and function: Effect of chronic vitamin C deficiency in guinea pigs

Abstract Chronic vitamin C deficiency was induced in guinea pigs by feeding a vitamin C-deficient diet, along with a maintenance dose of 0.5 mg ascorbic acid/day for 3 months. Intestinal uptake of alanine and leucine was significantly increased, but there was no change in the uptake of glucose and lysine in scorbutic guinea pigs. Intestinal transport of vitamin B 12 was depressed in scurvy. Brush border sucrase, alkaline phosphatase, and leucine aminopeptidase activities were considerably enhanced in scorbutic animals. It was revealed by kinetic studies with sucrase and alkaline phosphatase that activation of the sucrase is due to enhanced enzyme content, but stimulation of alkaline phosphatase occurs as a result of decrease in apparent K m of the enzyme in scurvy. Analysis of the chemical composition of the brush borders showed a significant augmentation in sialic acid, total lipids, phospholipids, and free-cholesterol contents of scorbutic membranes when compared to controls. The observed increase in membrane lipids is possibly due to enhanced synthesis, as suggested by the increased incorporation of radiolabeled acetate into these fractions in scurvy.