Duodenal Brush-border Mucosal Glucose Transport and Enzyme Activities in Aging Man and Effect of Bacterial Contamination of the Small Intestine

Duodenal biopsies were collected from 38 subjects (24 female and 14 male) ranging in age from 55 to 91 years. Evidence of bacterial contamination of the small bowel (BCSB) was sought at the same time by bacterial culture of duodenal aspirates and by hydrogen and [14C]glycocholic acid breath tests; subjects were considered to be positive for BCSB if any one of the three tests was abnormal. Biopsies were analyzed for six brush-border membrane enzyme activities: maltase, sucrase, lactase, alkaline phosphatase, leucine aminopeptidase, and alpha-glucosidase. Analysis of covariance with age as the covariate indicated no significant effect of age on the specific activities of these enzymes. Mucosal Na(+)-dependent glucose transport was quantified in brush-border membrane vesicles prepared from the biopsies. In all groups, glucose transport at 20-30 sec was greater (ranging from mean values of 2.45 to 3.66 times) than at 45 min, consistent with Na(+)-coupled glucose transport, and no significant effect of age was observed. BCSB had no significant effect on specific activities of any of the duodenal mucosal hydrolases but was associated with reduced (P = 0.05) brush-border glucose transport. None of the variables studied was significantly affected by the gender of subjects. In conclusion, these biochemical data do not support the contention that reduced capacity for carbohydrate absorption in the elderly is explained by reductions in duodenal brush-border mucosal disaccharidase activities or glucose transport.