Development of active and passive transport of bile acids in rabbit intestine

Previous studies have indicated that saturable, Na+-bile acid coupled transport is absent in the ileum throughout most of the suckling period and that the maturation of ileal bile acid uptake which occurs during weaning results primarily through an increase in functional bile acid carriers within the ileal brush border membrane. This study was undertaken in weanling and adult rabbits to establish the effect of maturation on the active ileal and passive jejunal and colonic uptake of 8 bile acids. The in vitro uptake of a range of concentrations of cholic (C), taurocholic (TC), glycocholic (GC), chenodeoxycholic (CDC), taurochenodeoxycholic (TCDC), glycochenodeoxycholic (GCDC), deoxycholic (DC) and taurodeoxycholic (TDC) acid was determined. Active ileal uptake of C, TC, GC, DC and TDC was greater in adult than in weanling animals, whereas uptake of CDC, TCDC and GCDC was similar in both groups. The relative permeability for passive uptake of bile acids into the jejunum and colon was similar in young and adult rabbits. Jejunal mucosal surface area was similar in the two groups, but was greater in the ileum in the adult than in the weanling rabbits due to an increase in villus height, width, and number of villi per unit serosal length. However, the age-associated differences in active bile acid uptake were not explained simply on the basis of these differences in ileal mucosal surface area or the concentration of bile acids in the intestinal lumen. Thus, maturation of the rabbit from weanling to adulthood does not influence the relative passive permeability of the jejunum or colon to bile acids, but does increase active ileal uptake of conjugated and unconjugated cholic acid and deoxycholic acid, but not chenodeoxycholic acid.