Role of estrogens in phenobarbital induction of microsomal enzymes of the liver]

The action of estradiol dipropionate (250 microgram/kg) and of phenobarbitone-sodium salt (80 microgram/kg) was studied in separate and combined (a single injection of estradiol-dipropionate after a 4-day administration of the phenobarbital-sodium salt) administration. There was an increase in the H3-phenylalanine incorporation into the cell-free protein-synthesizing system by 86% in comparison with control ovariectomized group. Under these conditions estradiol-dipropionate increased the incorporation of the labeled amino acid by 53%. A combined administration of the estrogen and of the barbiturate was not accompanied by the summation of the given effect. There was revealed a correlation between the increase in the rate of the H3-phenylalanine incorporation in vitro and an increase in the content of the cytochrome P-450 in vivo in the microsomes of hepatocytes in separate and combined administration of the preparations. The role of phenobarbitone-sodium salt as an activator of estradiol metabolism in the hepatocytes is discussed.     

Fatty acid composition and properties of the liver microsomal membrane of rats fed diets enriched with cholesterol.

Male rats were fed diets containing olive (OO) or evening primrose (EPO) oil (10% w/w), with or without added cholesterol (1% w/w). After 6-week feeding, the lipid and fatty acid compositions, fluidity, and fatty acid desaturating and cholesterol biosynthesis/esterification related enzymes of liver microsomes were determined. Both the OO and EPO diets, without added cholesterol, increased the contents of oleic and arachidonic acids, respectively, of rat liver microsomes. The results were consistent with the increases in delta 9 and delta 6 desaturation of n-6 essential fatty acids and the lower microviscosity in the EPO group. Dietary cholesterol led to an increase in the cholesterol content of liver microsomes as well as that of phosphatidylcholine (PC). The cholesterol/phospholipid and PC/PE (phosphatidylethanolamine) ratios were also elevated. Fatty acid composition changes were expressed as the accumulation of monounsaturated fatty acids, with accompanying milder depletion of saturated fatty acids in rat liver microsomes. In addition, the arachidonic acid content was lowered, with a concomitant increase in linoleic acid, which led to a significant decrease in the 20:4/18:2 ratio in comparison to in animals fed the cholesterol-free diets. Cholesterol feeding also increased delta 9 desaturase activity as well as membrane microviscosity, whereas it decreased delta 6 and delta 5 desaturase activities. There was a very strong correlation between fluidity and the unsaturation index reduction in the membrane. Furthermore, the activity of hydroxymethylglutaryl-CoA reductase increased and the activity of acyl-CoA:cholesterol acyltransferase decreased in liver microsomes from both cholesterol-fed groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Liver microsome phospholipids and cytochrome P.450 conceptration in phenobarbital treated rats fed on different diets

Liver microsomal concentration of cytochrome P.450 is increased in animals which are fed diets rich in polyunsaturated fatty acids. On the other hand, the effects of phenobarbital are more important when the dietary fat is more unsaturated. The unsaturation index in liver microsomal phosphatidylcholines depends on the unsaturation of the dietary fats. The treatment with phenobarbital constantly results in a decrease of the unsaturation index of fatty acids both in lecithins and cephalins. The importance of the liver microsomal cytochrome P.450 increase and the importance of the unsaturation index decrease in liver microsomal lecithins, both promoted by phenobarbital, are in good agreement.     

Effect of garlic oil extract on serum, liver and kidney enzymes of rats fed on high sucrose and alcohol diets

High levels of alkaline phosphatase and alcohol dehydrogenase were observed in the serum, liver and kidneys of rats fed on high sucrose and high alcohol diets over a period of 75 days. Garlic oil extract fed with any of the diets, significantly lowered the high levels of the two enzymes in the serum, liver and kidneys. This effect may be due to reduced biosynthesis of fatty acids as NADPH, required for the process, is utilised for the metabolism of the oil.     

Kinetic constant determination of liver microsomal and purified UDP-glucuronosyltransferase after phenobarbital and 3-methylcholanthrene treatments in rats

After induction by phenobarbital and 3-methylcholanthrene, UDP-glucuronosyltransferase involved mainly in the conjugation of planar substrates was purified. Compared to the microsomal enzyme, the purified protein exhibited less affinity towards the substrates, but the corresponding Vmaxs were increased. These results were attributed to a change in the lipid environment of the purified enzyme. The conjugation rate for 4-hydroxycoumarine was 15-45 times less than that measured for the 7-hydroxyisomer with the microsomal or the purified enzymes. Immunoprecipitation studies of the enzyme revealed that the two compounds were transformed by the same enzyme, or metabolized by two separate enzymes presenting the same antigenic site. The orientation of the hydroxyl group of planar aglycones in the active site is the determinant for the efficiency of catalysis.     

Zinc deficiency and the desaturation of linoleic acid in rats force-fed fat-free diets

Recent studies with rats force-fed zinc-deficient diets containing various types of fat failed to demonstrate a role of zinc in desaturation of linoleic acid. The present study was conducted to investigate the effect of zinc deficiency on desaturation of linoleic acid in rats that were initially force-fed fat-free diets to stimulate activity of desaturases. Therefore, rats were fed zinc-adequate and zinc-deficient fat-free diets for 6 d. After that period, the groups were divided and half of the rats continued feeding the fat-free diet for another 3.5 d whereas the other half was switched to a fat diet by supplementing the fat-free diet with 5% safflower oil. In order to assess desaturation of linoleic acid, fatty acid compositions of liver phosphatidylcholine, ethanolamine, and-serine were considered, particularly levels of individual (n-6) polyunsaturated fatty acids (PUFA). Levels of total and individual (n-6) PUFA were similar in zinc-adequate and zinc-deficient rats fed the fat-free diet throughout the experiment. Addition of 5% safflower oil increased levels of total and individual (n-6) PUFA in both zinc-adequate and zinc-deficient rats. However, total (n-6) PUFA in all types of phospholipids were higher in zinc-adequate rats than in zinc-deficient rats. Additionally, in zinc-deficient rats there were changes of (n-6) PUFA levels typical for impaired Δ5 and Δ6 desaturation: linoleic acid and dihomo-γ-linolenic acid were elevated; arachidonic acid, docosatetraenoic acid, and docosapentaenoic were lowered by zinc deficiency. Therefore, the study shows that zinc deficiency impairs desaturation of linoleic acid in rats force-fed fat-free diets and therefore supports results from former convential zinc deficiency experiments suggesting a role of zinc for desaturation of linoleic acid.     

Activities of liver microsomal fatty acid desaturases in zinc-deficient rats force-fed diets with a coconut oil/safflower oil mixture of linseed oil

The present study was conducted to investigate the effect of zinc deficiency on fatty acid desaturation in rats fed two different types of dietary fat, a mixture of coconut oil and safflower oil (7∶1, w/w, “coconut oil diet”) or linseed oil (“linseed oil diet”). In order to ensure an adequate food intake, all rats were force-fed by gastric tube. Zinc deficiency caused statistical significant reducion of Δ9-desaturase activity in liver microsomes of rats fed coconut oil diet and tendencial reduction (p<0.15) in rats fed linseed oil diet compared with control rats fed diets with the same type of fat. In agreement with this effect, zinc deficiency in the rats fed both types of dietary fat increased the ratio between total saturated and total monounsaturated fatty in liver phospholipids and liver microsomes. Zinc deficient rats on the coconut oil diet had unchanged Δ6-desaturase activity with linoleic acid as substrate and lowered activity with α-linolenic acid as substrate. In contrast, zinc deficient rats on the linseed oil diet had increased Δ6-desaturase activity with linoleic acid as substrate and unchanged activity with α-linolenic acid. Because linoleic acid is the main substrate for Δ6-desaturase in the rats fed coconut oil diet, and α-linolenic acid is the main substrate in the rats fed linseed oil diet, it is concluded that in vivo Δ6-desaturation was not changed by zinc deficiency in the rats fed both types of dietary fat. Activity of Δ5-desaturase was also not changed by zinc deficiency in the rats fed both dietary fats. Levels of fatty acids in liver phospholipids and microsomes derived by Δ4-, Δ5-, and Δ6-desaturation were not consistently changed by zinc deficiency in the rats fed both types of dietary fat. Thus, the enzyme studies and also fatty acid composition data of liver phospholipids and microsomes indicate that zinc deficiency does not considerably disturb desaturation of linoleic and α-linolenic acid. Therefore, it is suggested that similarities between deficiencies of zinc and essential fatty acids described in literature are not due to disturbed desaturation of linoleic acid in zinc deficiency. The present study also indicates that zinc deficiency enhances incorporation of eicosapentaenoic acid into phosphatidylcholine of rats fed diets with large amounts ofn-3 polyunsaturated fatty acids.     

Kinetics of CO binding to and dissociation from microsomal cytochrome P-450 induced by phenobarbital in rat liver

The kinetics of CO binding to hepatic microsomes from phenobarbital-treated Sprague-Dawley rats, measured by stopped flow spectrophotometry, can be resolved into three components with second order velocity constants of 2.23 +/- 0.35 X 10(5) M-1 S-1, 1.59 +/- 0.18 X 10(6) M-1 S-1, and 8.7 +/- 1.7 X 10(6) M-1 S-1. The three CO-binding species were present in ratios of 1:1.25:1.39 as judged by the relative amplitude of the change in absorbance at 450 nm associated with each of the kinetic components. Similar results were obtained in a range of [CO] from 10 to 700 micron when CO recombination was followed subsequent to flash photolysis of the CO-associated microsomes. In contrast, the dissociation rate of CO from its cytochrome P-450 complex measured by the NO replacement method was biphasic. Approximately 40% of the bound CO dissociated at a rate of 0.40 +/- 0.071 s-1, whereas the remaining 60% dissociated at a rate of 0.049 +/- 0.008 s-1 at 20 degrees C.     

Membrane homeostasis: thermotropic behaviour of microsomal membrane lipids isolated from livers of rats fed cholesterol-supplemented diets

Differential scanning colorimetry (DSC) has been applied to study the phase transition properties of isolated lipids from liver microsomal membranes of rats fed high cholesterol diets with or without high levels of either saturated (coconut oil) or unsaturated (sunflower seed oil) fat. DSC of aqueous buffer dispersions of liver microsomal lipids exhibited two independent, reversible phase transitions. The dietary cholesterol treatments had their major effect on the temperature at which the lower phase transition (T1) occurred. This transition occurred at a lower temperature when cholesterol was added to the diet, irrespective of the nature of the fatty acid supplement. However the magnitude of decrease was more when cholesterol was fed with sunflower seed oil. Inclusion of cholesterol into the rat diets also lowered the enthalpy values for the lower phase transition (T1). No appreciable effect on the temperature of the higher phase transition (T2) was observed, however the enthalpy values were slightly decreased by cholesterol feeding. These results suggest that certain domains of microsomal lipids, probably containing some relatively higher melting-point lipids, independently undergo solidus or gel formation and this transition (T2) is not greatly affected by dietary cholesterol. On the other hand, domains representing the bulk of the microsomal lipids undergo a phase change (T1) at temperatures which are dependent on cholesterol content and fatty acid profiles of the membrane, which are in turn, modified by dietary cholesterol intake.     

Plasma esterase activities in rats fed magnesium-deficient diets

In a study with rats it was determined whether dietary magnesium concentration affects plasma esterase activities. The feeding of a diet with 0.01% (w/w) instead of 0.04% magnesium reduced plasma magnesium concentration by 50%. Plasma total esterase, arylesterase and butyrylcholinesterase activities were significantly decreased in the magnesium-deficient rats. In rats fed a diet containing 0.02% magnesium, plasma magnesium concentration was lowered by 30%, and group mean plasma total esterase activity was decreased, but not the activities of arylesterase and butyrylcholinesterase.