Emilio Sanchez

Drug tolerance and detoxicating enzymes in Octodon degus and Wistar rats. A comparative study

Octodon degus shows greater tolerance to pentobarbital as compared with the Wistar rat. Mixed function oxidase activities in liver microsomes were higher in Octodon degus than in the Wistar rat. The reactions assayed were: aminopyrine N-demethylation, aniline and naphthalene hydroxylation and p-nitroanisole O-demethylation. These higher activities seem to be due mainly to the greater cytochrome P-450 content of liver microsomes of Octodon degus. Glutathione S-transferase activity towards 1-chloro-2,4-dinitrobenzene was 30 times higher in Octodon degus than in the Wistar rat. These results may explain the tolerance of Octodon degus to pentobarbital and other drugs.

Inhibition and activation of UDP-glucuronyltransferase in alloxanic-diabetic rats

Short or long term alloxan diabetes produced activation of oestrone and morphine glucuronidation and inhibition of p-nitrophenol glucuronidation in rat liver microsomes. Insulin treatment restored decreased glucuronyltransferase (GT) activity for p-nitrophenol and it did not abolish diabetes activation on oestrone glucuronidation. Triton X-100 detergent activation reduced differences between normal, diabetic and insulin treated rats in the glucuronidation rates of the substrates assayed. 1,4-Benzodiazepines inhibited morphine GT activity and stimulated oestrone GT activity in normal, diabetic and insulin treated diabetic rats. Activation and inhibition of GT activities for oestrone and xenobiotics in diabetes mellitus appears to be related with membrane perturbations of liver microsomes.

Enhanced metabolism of morphine in Octodon degus compared to Wistar rats

Comparative studies of the actions of morphine in different mammals have shown that Octodon degus presents an unusual tolerance to this compound. Morphine glucuronidation and N-demethylation in microsomal fractions of Octodon degus were 10.9 and 50.0 nmol of product formed/min/g of wet liver, respectively. In Wistar rat these activities were 10.5 and 12.5, respectively. Microsomal protein and cytochrome P-450 contents were two and four times higher in Octodon degus than in the Wistar rat, respectively. These results may explain the high tolerance to morphine presented by Octodon degus.

Increased activity of testosterone hydroxylases in liver microsomes of diabetic rats treated with insulin.

Liver microsomes from alloxan diabetic rats displayed decreased activity to hydroxylate testosterone only at the 2-alpha and 6-beta positions. Diabetic insulin-treated rats showed higher hydroxylase activities than diabetic and control rats in the formation of all testosterone metabolites analyzed. The sodium dodecylsulfate electrophoretic profile of liver microsomal proteins from each group of rats exhibited distinct increases as well as decreases in the cytochrome P-450 region. Stimulation of testosterone metabolism by insulin may be associated with a higher synthesis of certain cytochrome P-450 isozymes.

Drug metabolism in Octodon degus: Low inductive effect of phenobarbital

1. Differential effects of phenobarbital pre-treatment on liver microsomal drug metabolizing enzymes were registered in Octodon degus. 2. Glucuronidation reaction for morphine was decreased but that for p-nitrophenol was significantly increased. 3. Oxidative reactions such as naphthalene hydroxylation, morphine and aminopyrine N-demethylation were modestly increased. 4. In phenobarbital treated Octodon degus, testosterone metabolic pathways were decreased, not inducible or absent. 5. Spectral studies revealed two binding sites with different affinities for aniline in Octodon degus liver microsomes. 6. The poor phenobarbital induction on drug metabolism in Octodon degus may be a result of deficiency of androgen metabolic pathways associated to drug metabolizing enzymes.

Effects of chloroquine pretreatment on lethal dose of morphine and on morphine metabolism in rats

Abstract The previous administration of chloroquine to normal rats resulted in a significant increase in the lethal dose of morphine and in a higher amount of conjugated morphine in the liver. No differences were found on normorphine formation in liver of treated and untreated groups. The blood levels of free morphine at death were not significantly different in pretreated and control rats. Pretreatment with chloroquine did not prevent the onset of the depressant respiratory effects of morphine. Chloroquine pretreatment induced a marked increase of the in vitro conjugation of morphine, suggesting that chloroquine acts as a morphine antagonist through a metabolic mechanism. The implication of these effects on morphine tolerance are discussed.

DIABETES IN FEMALE RATS; CHANGES IN LIVER MICROSOMAL AMINOPYRINE N-DEMETHYLASE AND UDP-GLUCURONYL TRANSFERASE ACTIVITIES

SummaryShort or long term diabetes in female rats produced remarkable activation of aminopyrine N-demethylation, inhibition of oestrone and p-nitrophenol glucuronidation and no changes in morphine UDP-glucuronyltransferase activityin vitro. Km and Vmax for these reactions were determined. Insulin treatment partially antagonized diabetes activation of aminopyrine N-demethylation: it restored decreased UDPglucuronyltransferase activities for oestrone and p-nitrophenol only in long term and short term diabetes, respectively. Insulin also markedly inhibited morphine glucuronidation. Triton X-100 also displayed a differential pattern of activation for the glucuronidation reactions in liver microsomes of diabetic rats. Results suggest that diabetes in female rats may increase the actual amount of enzyme protein for aminopyrine metabolism and to decrease that for oestrone and p-nitrophenol.

Receptors for morphine and opioids

Two points concerning enzymatic systems acting on disposal of morphine are discussed, namely the multiplicity of glucuronyltransferase and the effect of nalorphine on N-demethylation of morphine. Evidences of the presence of at least two different glucuronyltransferases in microsomes of rat liver, kidney and intestine are presented. These evidences are given by the different distribution of the glucuronizing activity for morphine and rho-nitrophenol in microsomal preparations of these organs; by the different glucuronidation activity for both substrates induced by phenobarbital and 3-methylcholantrene; and finally by the chromatographic separation of fractions with enzymatic glucuronidating activity only for rho-nitrophenol or only for morphine. Nalorphine in concentrations of 1.3 X 10(-3) M and 1.3 X 10(-4) M inhibited in vitro de-N-demethylation of morphine 1.3 X 10(-3) M by the supernatant of rat liver homogenates, while in concentration of 1.3 X 10(-5) M it enhanced this reaction.