Eugenia Del Villar

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.

Comparison of alloxan and streptozotocin induced diabetes in rats: Differential effects on microsomal drug metabolism

1. Liver microsomes from alloxan or streptozotocin diabetic rats displayed differential drug metabolizing abilities in vitro. 2. Only streptozotocin liver microsomes exhibited changes in the cytochrome P-450 normal spectral characteristics. 3. Overall testosterone metabolism was significantly increased in streptozotocin diabetic liver microsomes, whereas it was markedly decreased in alloxan diabetes. Mixed function oxidase activity for aminopyrine was similar. 4. Glucuronidation reaction rates towards morphine, oestrone and p-nitrophenol were also markedly distinct in both models as well as after insulin treatment. 5. Results suggest that diabetogenic agents modify sex related isoenzymes of cytochrome P-450 differently and selectively reduce the synthesis of certain UDP-glucuronyltransferase forms.

Androstenedione metabolism in streptozotocin diabetes and fasting male rats: Similarities and differences

Abstract The oxidation products of androstenedione catalysed by liver microsomes from streptozotocin-diabetic and fasting male rats have been studied. Diabetic and starved rats displayed increased activity for 7α androstenedione hydroxylase and diminished activity for 16a androstenedione hydroxylase in comparison to the normal animals. Insulin treatment to diabetic rats did not antagonize the changes observed in untreated diabetic rats. Opposite to the diabetic state, the rate of 6β-OHA and 2β-OHA formation were increased in the course of the starved periods. The results suggest that under diabetes and fasting conditions distinct alterations occur in specific individual cytochrome P-450s.

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.

DDT-dehydrochlorinase. III. Enzymic oxidation of glutathione

Abstract 1. 1. Highly purified DDT-dehydrpchlorinase (E.G. 4.5.1.1) from DDT-resistant houseflies is able to act as a glutathione coddase. Both the monomeric and tetrameric forms of the enzyme show oxidation activity, which is lost by titration of the DDT-dehydrochlorinases thirty-two sulphydryl groups with PCMB. 2. 2. Conditions under which DDT-dehydrochlorinase undergoes glutathione oxidation are studied and compared with those of the ODT-dehydrochlorination activity of the enzyme. 3. 3. Of the compounds tested for the oxidation activity, only reduced glutathione and thioglycolic acid are substrates, the initial rate of oxidation of the latter being approximately three times that of GSH. 4. 4. The oxidation-reduction reaction does not involve liberation of protons in the presence of NAD or NADP. The transfer of the hydrogen atoms of the substrate and their subsequent oxidation to water is measured by oxygen consumption. The mechanism via O2- free-radical anions is postulated.

The effect of DDT treatment on the levels of DDT-dehydrochlorinase in Musca domestica

Abstract 1. 1. The levels of DDT-dehydrochlorinase (E.C. 4.5.1.1) measured in the soluble fraction obtained from homogenates of Musca domestica L. are increased after treatment of the insect with DDT. 2. 2. The increase enzymatic activity is shown to be paralleled by an increased de novo synthesis of the enzyme protein. 3. 3. Experiments using protein synthesis inhibitors suggested that this enhanced enzyme synthesis is dependent on RNA synthesis and gave further support to the idea of an inductive phenomenon.

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.