Bile loss in the acute intestinal radiation syndrome in rats.

The effects of bile duct ligation (BDL), choledochostomy, bile acid sequestering within the intestinal lumen by cholestyramine, and fluid and electrolyte replacement on survival time and development of diarrhea after whole-body exposure to doses of ionizing radiation that result in death from acute intestinal injury were studied. BDL significantly prolonged survival and delayed the onset of diarrhea after exposure to 137Cs gamma rays, fission neutrons, or cyclotron-produced neutrons in the range of doses that produce intestinal death or death from a combination of intestinal and hematopoietic injuries. Cannulation of the bile duct with exteriorized bile flow (choledochostomy) to protect the irradiated intestine from the mucolytic action of bile salts did not duplicate the effect of BDL in increasing survival time. Choledochostomy without fluid replacement eliminated the occurrence of diarrhea in 15.4 Gy irradiated rats. Diarrhea did occur in irradiated animals with choledochostomy if they received duodenal injections of fluid and electrolytes to replace the fluid lost as a result of bile drainage. Duodenal injection of fluid and electrolytes, however, had no significant effect on survival time in irradiated rats. In contrast, injection of fluid and electrolytes into the peritoneal cavity of irradiated rats resulted in an increase in survival time that was comparable to that observed after BDL. Addition of antibiotics to the peritoneally injected fluid and electrolytes further increased survival time (up to 9 days). This survival time approached that seen in animals receiving the same radiation dose but which had the intestine exteriorized and shielded to minimize radiation injury to the intestine. Postmortem histological examinations of the irradiated small intestine showed mucosal regeneration in these long-term survivors receiving fluid and antibiotic therapy. In contrast, duodenal injection of cholestyramine post irradiation to bind bile acids had no effect on survival time or diarrhea incidence. The conclusions from these experiments are that BDL prolongs survival and postpones the onset of diarrhea in irradiated rats dying from acute intestinal injury primarily by slowing down the loss of fluid and electrolytes and that bile acids play no significant role.

Effects of single-dose and repeated-dose pretreatment with 2(3)-tert-butyl-4-hydroxyanisole (BHA) on the hepatobiliary disposition and covalent binding to DNA of aflatoxin B1 in the rat.

The effects of two distinctive BHA pretreatment regimens on the biliary excretion of aflatoxin B1 (AFB) metabolites and the covalent binding of AFB to hepatic DNA were studied in vivo in the rat. To differentiate between enzyme induction effects and direct antioxidant effects, BHA was given to rats for 9 days (500 mg/kg/day, sc) or as a single dose (500 mg/kg, po), and [3H]AFB was administered ip. Repeated treatment with BHA enhanced the biliary excretion of both the glutathione conjugate of AFB and the AFP1-glucuronide to 200% of control values, reduced the amount of AFB remaining in the liver to 53% of control and reduced the covalent binding of AFB to hepatic DNA to 16% of control. A single BHA treatment had no effect on the biliary excretion of AFB or the binding of AFB to hepatic macromolecules, even though high concentrations of BHA were present in the liver during the period of AFB metabolism. These results support the hypothesis that BHA inhibits AFB carcinogenesis via the induction of phase II biotransformation pathways such as glutathione S-transferase, which act to reduce the amount of AFB-epoxide available for binding to DNA. We found no evidence of a direct antioxidant effect of BHA in altering the hepatobiliary disposition of AFB.

Effects of phenobarbital on the biliary excretion of aflatoxin P1-glucuronide and aflatoxin B1-S-glutathione in the rat.

Direct h.p.l.c. analysis of bile separated at least five major water-soluble metabolites of AFB; the two most prevalent AFB metabolites were identified as AFB-S-glutathione (AFB-GSH) and AFP1-glucuronide, which accounted for 49-57% and 4-15% of total biliary AFB metabolites, respectively. In the two hours following AFB administration, phenobarbital-treated rats eliminated 50% more AFB-derived radioactivity in bile compared with controls. No qualitative differences in the profile of biliary AFB metabolites were noted between phenobarbital-treated and control rats. However, a 90% increase in the rate of excretion of AFB-GSH was found in phenobarbital-treated animals. Phenobarbital treatment had no significant effect on the amount of AFB remaining in the liver after two hours, but decreased the amount of AFB covalently bound to hepatic DNA by 55%. When individual animals from both control and phenobarbital-treated groups were considered, the correlation between the increase in excretion of AFB-GSH and the decrease in covalent binding was significant with a correlation coefficient of 0.77. This finding is consistent with the hypothesis that induction of GSH S-transferase is responsible for the anticarcinogenic effects of phenobarbital towards AFB-induced hepatocarcinogenicity, although changes in the rate of formation of aflatoxin P1 or other biotransformation pathways may also be important.