Intestinal morphology, marker enzymes and lipid content of brush border membranes from rabbit jejunum and ileum: effect of aging

Abstract

Aging is associated with changes in the intestinal uptake of nutrients. This study was undertaken to determine whether the morphology, enzyme markers and the lipid content of the intestinal brush border membrane (BBM) was influenced by aging. There was an increase in the height of the jejunal villi and number of cells/villus, resulting in an age-related increase in the jejunal villus and mucosal surface area in young as compared with weaning rabbits. In mature 1-year-old animals, there was a decline in villus height, number of cells/villus, and mucosal surface area, so that the jejunal characteristics of the mature animals resembled those of the weanling rabbits. In the ileum, aging was associated with an increase (weanling vs. young), then a decrease (young vs. mature) in the height of the villi, and the number of cells/villus. Aging had no effect on the size of the villus cells. At all ages there was a direct positive relationship between the height of the villi and the mucosal surface area, and between villus surface area and sucrase activity. An established technique was used to purify rabbit BBM and to measure the BBM content of enzyme markers and lipids in weanling, young and mature animals. Both the BBM sucrase (S) and alkaline phosphatase (AP) increased in young as compared with weanling rabbits, and the ratio of AP/S remained unchanged. The S remained high in mature rabbits, but AP declined, so that AP/S fell. There was a positive linear correlation between S and villus surface area. In weanling rabbits, the total BBM phospholipid content and the ratio of total phospholipid/total cholesterol were lower in the ileum than in the jejunum. In the jejunal BBM of young animals, there was more total free fatty acids and cholesterol ester than in the weanling jejunum. The jejunal BBM total phospholipids and total cholesterol were higher in the mature than in the weanling animal jejunum when expressed as nmoles/mg protein, but the ratio of total phospholipid/total cholesterol was unaffected by aging. The greatest percentage of jejunal BBM phospholipid