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“Enterohepatic recycling of phenolphthalein, morphine, lysergic acid diethylamide (LSD) and diphenylacetic acid in the rat: Hydrolysis of glucuronic acid conjugates in the gut lumen”. 
Xenobiotic. 1980;10(9):689-703.
1. Biliary elimination in female Wistar albino rats 3h after i.p. injection of [3H]phenolphthalein, [3H]morphine, 14C-LSD and [14C]diphenylaeetie acid was 90%, 45%, 75% and 57% respectively, predominantly as glueuronides. 2. Infusion of 3 h bile from the previous experiments into the duadena of bile-duet-cannulated animals demonstrated enterohepatie circulation, amounting in 24h to 85%, 41%, 28% and 660f the infused doses of the conjugates of phenolphthalein, morphine, LSD and diphenylaeetic acid respectively. 3. Pretreatment with antibiotics to suppress intestinal microflora decreased this enterohepatic recirculation to 22%, 8 6% and 2 l 0n 24 h for phenolphthalein, morphine and diphenylacetic acid glucuronides respectively. Antibiotic pretreatment did not influence the absorption and re-exeretion of infused doses of the free aglyeones, thus demonstrating the importance of bacterial beta-glucuronidase hydrolysis of the biliary conjugates. 4. The extent of intestinal absorption of the aglyeones after bacterial beta-glucuronidase hydrolysis of the conjugates is related to their lipid-solubility as estimated by oetan-l-ol: 0.1 M phosphate buffer partition ratios (P-values). 5. The persistence of compounds in the enterohepatic circulation is determined by the faecal and urinary elimination of the circulating compounds. Faecal elimination is governed by the extent of intestinal absorption of the circulating compounds, which is influenced by the efficacy of intestinal hydrolysis of the conjugates and the relative lipophilicity of the aglycones released.
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