Intestinal uptake of bile acids: effect of external abdominal irradiation

Abdominal irradiation has recently been shown to influence the uptake of hexoses, amino acids, fatty acids and cholesterol into the jejunum of rats. The present studies were undertaken with a previously validated in vitro technique to determine the effect of abdominal irradiation from a cesium 137 source on the rates of uptake of six bile acids into the jejunum, ileum, and colon. In the ileum of control rats, there were marked differences in the value of the apparent Michaelis constant (Km*), maximal transport rate (Jdm), and apparent passive permeability coefficient (Pd*) between cholic (C), glycocholic (GC), taurocholic (TC), chenodeoxycholic (CDC), and glycochenodeoxycholic (GCDC), and deoxycholic (DC) acid. The Km* for each bile acid except DC was lower three and 14 days after 600 rad, whereas the Jdm for GC fell, but rose for TC, CDC, GCDC and DC and was unchanged for C. The Pd* rose for C, GC, and DC, fell for TC and CDC, but remained unchanged for GCDC 14 days after irradiation. After 600 rad the value of Pd* in the colon was increased at day 3 and 14 for CDC and GCDC, but was unchanged for GC and TC and was decreased for C. The uptake of bile acids was also affected by 300 rad and by 900 rad, but the direction and magnitude of the change was influenced by the intestinal site, the dose of irradiation, and the type of bile acid. The results show that: 1) there likely are multiple ileal carriers for bile acids; 2) abdominal irradiation has a variable effect on these carriers; 3) the passive permeability to bile acids varies with the bile acid and with the site along the intestine; and 4) abdominal irradiation is associated with a rise in the colonic permeability to only some bile acids.