Bile-duct cannulated studies

In one study where a single 200 mg/kg dose was given to rats by gavage, 35% of the label was found in the bile in the first 2 days after dosing. The biliary label was equally distributed over the 2 days of collection. In a different study, 66% of a 1 mg/kg dose was excreted in the bile of bile duct cannulated rats in 72 hours and 58% of a 100 mg/kg dose (Payan et al. 1991). 

Direct excretion of metabolites into the bile via transporter-mediated efflux can be an important determinant of clearance and first-pass extraction.79-81 This phenomenon is probably much more common than it would seem from the literature, at least in part because there are no facile ways to study the effect other than in vivo using bile duct cannulated rats. 

The bioavailability of the radiolabeled bound residues of (XVI) and (XVII) is being investigated following oral administration to bile duct-cannulated rats. The outcomes of these studies are still being analyzed and only initial results are presented. Experiments were conducted in accordance with the UK Home Office regulations for animal welfare. 

The methods outlined above may not lead to a satisfactory determination of mechanism of incomplete bioavailability and additional methods may be necessary in some cases to fully characterize the factors responsible. Bile duct cannulated animals provide a powerful model to examine incomplete bioavailability issues, and the rat provides the most flexibility because terminal studies can routinely be done. For compounds that are thought to have dissolution limitations or instability in the GI tract, the GI tract can be removed at the end of the experiment and the contents assayed for drug and metabolites. The amount of parent in bile and urine can be quantitated by LC/MS/MS and this method can also be used for any metabolites where authentic standards have been prepared. 

For example, van Heek and coworkers observed a lead candidate that underwent extensive first-pass metabolism and yet elicited a significant level of pharmacological activity (van Heek et al., 1997). To evaluate the biological activity of the in vivo biotransformation products, they collected samples of bile from rats dosed with a lead compound and directly administered the samples to a bile duct cannulated rats via an intraduodenal cannula. As a control study, the parent compound prepared in a blank bile was dosed in a similar fashion to the recipient rats. The results indicated that the in vivo activity elicited by the bile samples was higher than the parent control sample, clearly indicating the presence of an active metabolite(s) that was more potent than the parent compound. To identify the active component, the bile sample was then fractionated and each fraction tested for biological activity. The structure of the metabolite was then established following the detection of the active fraction. As mentioned before, further modification of the active metabolite led to the discovery of ezetimibe. 

In a second study by Prout and Howard (1985b), the tissue distribution and excretion of [ " C]-alcohol-Iabeled tefluthrin was followed after the oral administration of 10 mg/kg to four male and four female rats in com oil. The animals were individually housed in metabolism cages for daily collections of urine and feces over a 7-days period. Rats were terminated at the end of 7 days and individual tissues harvested for the determination of radioactivity. A further set of two males and two females were administered an oral dose of 1.0 mg/kg [ " C] alcohol-labeled tefluthrin, after bile duct cannulation. Urine, bile, and feces were collected for a period of 48 h. Signs of acute toxicity were observed in the 10 mg/kg rats. Males excreted slightly less in urine (26% vs. 33%) and more in feces (68% vs. 63%) than females. In the bile duct study, males excreted 5-16% and females 8-10% of total radioactivity. 

The distribution of radiolabel in excreta was measured in male rats for the 72 hour period after intravenous administration of doses of 1 or 100 mg/kg (Payan et al. 1991). At both doses about 8% of the radiolabel was exhaled. The amount of label in the urine was 21% of the low dose and 9% of the high dose the amount in the feces was 59% of the low dose and 72% of the high dose. In a parallel study, the fecal, urinary, and biliary excretions were measured for rats with cannulated bile ducts. The urine contained 6-7% of the dose and the feces less than 0.5% for both doses. The bile contained 89% of the 1 mg/kg dose and 72% of the 100 mg/kg dose. 

Rats weighing 150-200 g are used. Eighteen hours prior to the experiment food is withdrawn with free access to water. The appropriate size of the study groups for the control and candidate compound consists of 5-7 animals. Anesthesia is induced by pentobarbital (priming bolus 60 mg/kg i.p. plus infusion s.c. at about 20 mg/kg/h) or i.p. injection of 5 ml/kg of 25 % urethane solution. Body temperature is artificially stabilized by means of a rectal thermometer and a heating pad. The trachea is exposed and cannulated for artificial respiration. The abdomen is opened by a mid-line incision and the pylorus ligated. The proximal part of the bile duct is ligated near the hepatic... 

Alvarez and Lopez (1989) studied the effect of alloxan diabetes on exocrine pancreatic secretion in the anesthetized rabbit. After a 14-15 hours fasting period, but with free access to water, rabbits weighing about 2.0 kg are anesthetized by intravenous injection of 1.0 g/kg urethane. After tracheotomy, a median laparotomy is performed, the main pancreatic duct is exposed and cannulated near its entrance to the duodenum following ligation of the pylorus and cannulation of the bile duct for deviation of bile to the exterior. 

Properties of MAP and preMAP conjugates which influence the extent of the enterohepatlc circulation of intact MAP and preMAP metabolites are not known. Differences in enterohepatlc circulation can be deduced from levels of excretion of MAP and preMAP metabolites by control rats and rats with cannulated bile ducts. Data from 2-chloro- isopropylacetanilide (10) and naphthalene (11) metabolism studies are given in Table II. It is apparent that the acetanilide biliary MAP metabolites were not absorbed from the intestine for excretion as mercapturic acid, but were absorbed as intestinal catabolites of MAP metabolites (23%) and excreted with the urine. 

Cannulation of the bile duct and removal of bile have been effective in dog studies. 

The effects of a short-time interruption (24 hours) of the enterohepatic circulation on bile composition has also bfjeu studied in man. At the time of operation on patients with cholelithiasis, Thurciborn (1962) cannulated the common bile duct with a ballenterohepatic circulation. Interruption of the EHC resulted in a decrease in the secretion of bile acid conjugates in the same way as in the bile fistula rats. In addition, the secretion of phospholipids decreased considerably, but the cholesterol output from the liver was about the same as with an intact enterohepatic circulation. Tlie decrease in phospholipid secretion is an interesting finding. Several explanations are possible. The occurrence of an enterohepatic... 

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