Catalytic activities of cytochrome P450 enzymes and UDP-glucuronosyltransferases involved in drug metabolism in rat everted sacs and intestinal microsomes.
1. The use of everted sacs of the small intestine as an enzyme source for studying the metabolism of xenobiotics by cytochrome P450 (P450, CYP) enzymes and UDP-glucuronosyltransferases has been investigated. 2. Most of the drug oxidation activities for testosterone, bufuralol, ethoxyresorufin and 7-ethoxycoumarin resided in the upper part of the everted sacs and in intestinal microsomes. Testosterone 6 beta-hydroxylase activities in the everted sacs were about two times higher than those in the intestinal microsomes. By freezing and thawing treatment, the testosterone 6 beta- and 16 alpha-hydroxylase activities of the everted sacs were considerably decreased, and those of the intestinal microsomes were abolished. 3. Microsomal testosterone 6 beta-hydroxylation, bufuralol 1'-hydroxylation, and pentoxyresorufin and ethoxyresorufin O-dealkylation were inhibited by ketoconazole, quinine, metyrapone and alpha-naphthoflavone respectively. Immunoreactive proteins using anti-CYP2B1 and anti-CYP3A2 antibodies were detected in the upper and middle parts of the rat small intestine. 4. Except for morphine 3-glucuronidation, glucuronidation activities in intestinal microsomes or everted sacs were not dependent on the intestinal region. The lower part of the everted sacs exhibited about 10 times higher morphine-3-glucuronidation activities compared with those of the upper part. The glucuronidation activities of 4-nitrophenol in the everted sacs were 10 times higher than those in microsomes. 5. These results demonstrated that the upper part of rat small intestine serves as the major site for intestinal P450-mediated first-pass metabolism. CYP3A enzymes in rat intestinal microsomes may not be stable but probably play an important role in drug oxidations. The high activity of glucuronidation in the rat small intestine should also be considered in terms of drug metabolism.
Takemoto
K
K
Faculty of Pharmaceutical Sciences, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-0934, Japan.
Yamazaki
H
H
Tanaka
Y
Y
Nakajima
M
M
Yokoi
T
T
D000319:Adrenergic beta-Antagonists / Q000378:metabolism; D000818:Animals; D002384:Catalysis; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004983:Ethanolamines / Q000378:metabolism; D005615:Freezing; D020719:Glucuronides / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015151:Immunoblotting; D007422:Intestines / Q000201:enzymology*; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D009020:Morphine / Q000378:metabolism; D009284:Naphthols / Q000378:metabolism; D009596:Nitrophenols / Q000378:metabolism; D010084:Oxidation-Reduction; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013739:Testosterone / Q000378:metabolism; D015262:Xenobiotics / Q000378:metabolism
D000319:Adrenergic beta-Antagonists; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D004983:Ethanolamines; D020719:Glucuronides; D009284:Naphthols; D009596:Nitrophenols; D004364:Pharmaceutical Preparations; D015262:Xenobiotics; C029350:1-naphthol; D013739:Testosterone; D009020:Morphine; C010831:bufuralol; D003577:Cytochrome P-450 Enzyme System; D014453:Glucuronosyltransferase; C024836:4-nitrophenol