Patricio Vega

Dietary fish oil and cytochrome P-450 monooxygenase activity in rat liver and kidney

Lauric acid hydroxylation and aminopyrineN-demethylation were studied in kidney and liver microsomes from rats treated with fish oil. Different doses of fish oil containing 20% eicosapentaenoic acid and 10% docosahexaenoic acid were provided daily to the rats for seven days. In all the groups studied, the lauric acid metabolism was higher in kidney microsomes and the aminopyrine metabolism in the liver microsomes. Although no effect on the renal cytochrome P-450 concentration was detectable, all four fish oil doses increased the hepatic concentration of cytochrome P-450 by a mean 27%. The higher fish oil doses used increased the renal and hepatic microsomal metabolism of aminopyrine. The lauric acid metabolism was increased by fish oil only in the liver. Fish oil, a known inducer of fatty acid peroxisomal β-oxidation, also induced microsomal activity. These results show that liver and kidney respond in different ways to dietary factors such as fish oil. In addition, our study would suggest that fish oil increased the activity of two different families of liver cytochrome P-450. The activity of kidney lauric acid 11- and 12-hydroxylation, however, was not modulated by fish oil.

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.

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.

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.

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.

Kidney drug metabolizing activities in streptozotocin diabetic rats

1. Streptozotocin-induced diabetes produced significant changes on the drug metabolizing enzyme machinery of rat kidney microsomes. 2. It reduced the cytochrome P-450 content by 30%, this effect being reversed by insulin therapy. 3. Total androstenedione oxidative metabolism was increased 2.5-fold and insulin treatment partially antagonized this activation. 4. Total testosterone hydroxylase activities were not modified by diabetes nor by insulin but the formation of 2 alpha OH testosterone and 6 beta OH testosterone were distinct in diabetes or insulin treated diabetic rats. 5. Only UDP-glucuronyltransferase activity for PNP was found in kidney microsomes. Diabetes determined a lower UDPGT substrate efficiency not reversed by insulin therapy.

Role of glucose-1-phosphate and glucose-6-phosphate in glycogen synthesis by pigeon liver homogenate☆

Abstract 1. 1. Glucose-1-C 14 , G-6-P-1-C 14 and G-1-P-l-C 14 have been incubated with a pigeon liver homogenate. Incorporation of C 14 into glycogen and CO 2 were measured. 2. 2. The relative incorporation of C 14 from G-6-P-1-C 14 and glucose-1-C 14 into glycogen and CO 2 together with the relative incorporation of C 14 from G-1-P-l-C 14 and glucose-1-C 14 into glycogen and CO 2 were calculated. From these results, it is postulated that G-6-P is not a necessary intermediate in glycogen biosynthesis from glucose; G-1-P would be the first intermediate and the metabolic cross that leads to glycogen and CO 2 . 3. 3. It is suggested that G-1-P is formed directly from glucose through the reactions catalyzed by phosphoglucokinase (E.C. 2.7.1.10) and phosphodismutase (E.C. 2.7.1.41). 4. 4. This last hypothesis is supported by the fact that G-1-P and G-1,6-diP stimulated C 14 incorporation from glucose-1-C 14 into both CO 2 and glycogen. Other minor facts obtained from this work and others from the literature help to sustain the postulations here discussed.