ABSTRACT
The hydroxylation of debrisoquine was investigated in Sprague-Dawley (SD) and Dark-Agouti (DA) rats. Female and male rats were phenotyped in-vivo with debrisoquine six times during their growth. The ratios debrisoquine/4-hydroxydebrisoquine of the female DA rats increased until the 15th week and then decreased; but the values of the metabolic ratios never exceeded 2. Female DA rats cannot be considered as genetically deficient for hydroxylation of debrisoquine in regard to the metabolic ratio, but the percentage of debrisoquine excretion is up to ten fold higher than that in the other strains. Therefore SD and DA rat livers were perfused for 2 h when the clearance of debrisoquine was significantly lower in the female DA group than in the other groups. 4-Hydroxydebrisoquine in the perfusate increased with time, but the amount after 120 min was 12 fold lower in the female DA rat group than in the female SD rat group. The results of the male DA group fell between. This study confirms that female DA rats present a lower debrisoquine 4-hydroxylating capacity than other rats but shows that urinary metabolic ratio is not sufficient to assess the deficiency of debrisoquine hydroxylation.
Subject(s)
Debrisoquin/metabolism , Isoquinolines/metabolism , Liver/metabolism , Animals , Body Weight , Debrisoquin/analogs & derivatives , Female , Hydroxylation , In Vitro Techniques , Indicators and Reagents , Male , Organ Size , Rats , Rats, Inbred StrainsABSTRACT
The metabolism of albendazole (ABZ) was studied in perfused livers from control and ABZ-treated rats (10.6 mg/kg, per os, each day for 10 days). In the perfusion fluid, the concentration of ABZ-sulfoxide (SO-ABZ) remained unchanged in treated, as compared to control animals, whereas ABZ-sulfone (SO2-ABZ) was increased in treated animals. In bile, only SO-ABZ was present. The transformation kinetics of SO-ABZ to SO2-ABZ in microsomes from rats treated with ABZ, 3-methylcholanthrene, Aroclor and isosafrole were biphasic. This suggests that enzyme activity was a consequence of two enzyme systems, one characterized by low affinity and high capacity, the other by high affinity and low capacity, the latter could be induced by 3-methylcholanthrene, ABZ, Aroclor and isosafrole. Cytochrome P-450c was induced potently in vivo by ABZ as proven by increased monooxygenase (7-ethoxyresorufin and 7-ethoxycoumarin-O-deethylase) activities and by Elisa test (a 5-fold increase in hemoprotein concentration was observed). Purified and reconstituted cytochrome P-450c from 3-methylcholanthrene or ABZ-treated rat liver were able to produce SO2-ABZ (2.01 and 1.70 nmol/mg/15 min, respectively, whereas cytochrome P-450b produced 10 times less SO2-ABZ). Immunological assays, as well as activity measurements showed a relationship between cytochrome P-450c-3-methylcholanthrene and cytochrome P-450c-ABZ. We conclude that induction of cytochrome P-450c by ABZ is the probable explanation for the enhanced formation of SO2-ABZ in vivo.
Subject(s)
Anthelmintics/metabolism , Benzimidazoles/metabolism , Cytochrome P-450 Enzyme System/metabolism , Microsomes, Liver/metabolism , Albendazole , Animals , Aroclors/pharmacology , Benzimidazoles/analysis , Biotransformation , Electrophoresis, Polyacrylamide Gel , Male , Methylcholanthrene/pharmacology , Microsomes, Liver/drug effects , Microsomes, Liver/enzymology , Rats , Rats, Inbred Strains , Safrole/pharmacologyABSTRACT
A general and sensitive HPLC method using a precolumn switching system was developed for the separation and quantification of the individual diastereoisomeric glucuronides of the 2-phenylpropionic acid optical isomers. Kinetic properties of rat liver glucuronidation of several arylcarboxylic acids (1- and 2-naphthylacetic acids, clofibric acid, (R)-(-)- and (S)-(+)-2-phenylpropionic acids) are characterized. The results show that rat liver microsomes glucuronidate 1-naphthylacetic acid more efficiently than its regioisomer (higher Vmax/Km ratio because of a 6-fold lower Km value). Furthermore, 2-phenylpropionic acid glucuronidation occurs stereoselectively and is characterized by an enantiomeric ratio R/S = 1.60. Specific inducers of different UDP-glucuronosyltransferase isoforms and the Gunn rat strain are used to define the substrate specificity of the conjugation reaction towards arylcarboxylic aglycones. Acyl glucuronide formation is induced by phenobarbital. Gunn rats are not deficient in conjugation of these arylcarboxylic acids. These results indicate that these compounds behave similarly to classically defined group 2 substrates. In addition, the stereospecificity of 2-phenylpropionic acid conjugation is unchanged by pretreatment of animals with inducers, in vitro detergent activation, and enantiomeric inhibition. This suggests that the optical isomers of 2-phenylpropionic acid can be either conjugated by the same form or very closely regulated forms of UDPGT.
