Dietary orotic acid accentuates the hepatic response to phenobarbital in rats

1990 ◽  
Vol 68 (9) ◽  
pp. 1146-1149 ◽  
Author(s):  
D. S. Milton Haines ◽  
Margaret Wu ◽  
Sonya D. Tokmakjian
Keyword(s):  
Endoplasmic Reticulum ◽  
Total Protein ◽  
Orotic Acid ◽  
Smooth Endoplasmic Reticulum ◽  
Limiting Factor ◽  
Semisynthetic Diet ◽  
Structural Framework ◽  
Cytochrome P 450 ◽  
Phosphatidylcholine Synthesis ◽  
Stimulation Of

In rats treated with phenobarbital for 3 days and simultaneously fed a semisynthetic diet containing 1.0% orotic acid, the extent of the increases in liver microsomal phosphatidylcholine, phosphatidylethanolamine, total RNA, total protein, and cytochrome P-450 were significantly greater than they were in rats treated identically with phenobarbital but without dietary orotic acid. This is attributed primarily to the stimulation of hepatic phosphatidylcholine synthesis by dietary orotic acid. In the absence of phenobarbital, orotic acid was shown to cause some increase in liver smooth endoplasmic reticulum components, but not cytochrome P-450. Orotic acid also decreased the activity of microsomal phosphatidylethanolamine N-methyltransferase, which may have contributed to the increase in the microsomal content of phosphatidylethanolamine. The hypothesis is advanced that phospholipid availability is a limiting factor in the hepatic response to phenobarbital. When more phospholipid is available to provide the structural framework for biogenesis of endoplasmic reticulum, all of the hepatic actions of phenobarbital, including induction of cytochrome P-450, are amplified.Key words: phosphatidylcholine, phosphatidylethanolamine, cytochrome P-450, phenobarbital, orotic acid, endoplasmic reticulum.

scholarly journals The distribution of the components of mixed-function oxidase between the rough and the smooth endoplasmic reticulum of liver cells

1968 ◽  
Vol 110 (3) ◽  
pp. 407-412 ◽  
Author(s):  
J. L. Holtzman ◽  
T. E. Gram ◽  
P. L. Gigon ◽  
J. R. Gillette
Keyword(s):  
Endoplasmic Reticulum ◽  
Smooth Endoplasmic Reticulum ◽  
Reductase Activity ◽  
Mixed Function Oxidase ◽  
Protein Ratio ◽  
Nadph Cytochrome ◽  
Rate Limiting Step ◽  
Significant Difference ◽  
The Difference ◽  
Cytochrome P 450

Mixed-function oxidase activity, when measured by the N-demethylation of ethylmorphine or the hydroxylation of aniline, is significantly higher in the smooth hepatic endoplasmic reticulum than in the rough. In the rabbit the smooth membrane/rough membrane activity ratios are significantly greater than 1 whether the activities are expressed per g. of liver (ratio 5), per mg. of protein (ratio 3–5), per μg. of phospholipid phosphorus (ratio 2), per unit of cytochrome P-450 (ratio 1·7) or per unit of NADPH–cytochrome c reductase activity (ratio 2). On the other hand, if the activities are normalized to the NADPH–cytochrome P-450 reductase, there is no significant difference between the rough and smooth membranes. These results suggest that, in the rabbit, the rate-limiting step is the reduction of cytochrome P-450. In contrast, in the rat the difference in activities can be explained by differences in the concentration of cytochrome P-450.

Actions of dietary orotic acid on liver synthesis of phosphatidylcholine and phosphatidylethanolamine in rats

1987 ◽  
Vol 65 (2) ◽  
pp. 105-111 ◽  
Author(s):  
D. S. Milton Haines ◽  
Sonya D. Tokmakjian
Keyword(s):  
Orotic Acid ◽  
Total Radioactivity ◽  
Intragastric Administration ◽  
Semisynthetic Diet ◽  
Catalytic Activities ◽  
Phosphatidylcholine Synthesis ◽  
Liver Phosphatidylcholine

The in vivo rates of the reactions of the cytidine pathways of liver phosphatidylcholine and phosphatidylethanolamine synthesis were measured in rats after 1 day of feeding on a semisynthetic diet containing 1% orotic acid. The calculations were made from the specific and total radioactivity versus time curves of the precursors and products following intraportal injection of [1,2-14C]choline, [2-14C]ethanolamine, and [2-3H]glycerol. The liver CTP level was increased twofold and the rates of CDP-choline and phosphatidylcholine synthesis were stimulated 4.5-fold in the rats fed orotic acid. The rate of CDP-ethanolamine synthesis was increased but could not be accurately quantified because of its extreme rapidity. No change occurred in the rate of the ethanolaminephosphotransferase reaction and the overall rate of phosphatidylethanolamine synthesis was unchanged by orotic acid feeding. The catalytic activities of the enzymes of the cytidine pathways of phosphatidylcholine and phosphatidylethanolamine synthesis were not affected by feeding orotic acid for 1 day. Similar findings were obtained 3 h following intragastric administration of 100 mg of orotic acid. The results suggest the possibility that changes in the levels of liver CTP may play a role in regulation of the cytidine pathway of liver phosphatidylcholine synthesis but not of phosphatidylethanolamine synthesis, because the latter pathway appears to be tightly controlled at the ethanolaminephosphotransferase step.

Induction of cytochrome P-450 in a selective subpopulation of hepatocytes

1978 ◽  
Vol 234 (3) ◽  
pp. C102-C109 ◽  
Author(s):  
J. J. Gumucio ◽  
L. J. DeMason ◽  
D. L. Miller ◽  
S. O. Krezoski ◽  
M. Keener
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Inductive Effect ◽  
Specific Activity ◽  
Smooth Endoplasmic Reticulum ◽  
Cell Subpopulation ◽  
Continuous Density ◽  
Liver Cytochrome ◽  
Cytochrome P 450 ◽  
In Cells

The objective of this study was to determine whether the inductive effect of phenobarbital (PB) on liver cytochrome P-450 was the result of the action of this drug on all or some hepatocytes. For this purpose, a light (cell band I) and a heavy (cell band II) subpopulation of hepatocytes were separated from rat liver in a continuous density gradient. To determine the location of these hepatocytes in tissue, [14C]bromobenzene, which binds covalently to centrilobular hepatocytes, was administered. The specific activity (14C dpm/mg protein) was greater in cells of band I than in cells of band II, suggesting a predominant contribution of centrilobular hepatocytes to the lighter cell band. Microsomes were separated from each cell subpopulation after 3 days of PB administration and cytochrome P-450 was measured. Although a fivefold increment in cytochrome P-450 content of light hepatocytes was noted, the content of heavy hepatocytes was similar to that of the respective subpopulation in controls. Concomitantly, PB administered for 3 days induced the smooth endoplasmic reticulum of centrilobular hepatocytes only, as revealed by electron microscopy of whole tissue. These results indicated that PB induces cytochrome P-450 in a selective subpopulation of hepatocytes, most likely located near the terminal hepatic venule.

scholarly journals The use of proteinases to determine the topological location of cytochrome P-450 in vesicles derived from smooth endoplasmic reticulum of rat liver

1981 ◽  
Vol 196 (2) ◽  
pp. 585-589 ◽  
Author(s):  
M B Cooper ◽  
M R Estall ◽  
B R Rabin
Keyword(s):  
Lipid Peroxidation ◽  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Phosphatase Activity ◽  
Rat Liver ◽  
Smooth Endoplasmic Reticulum ◽  
Transverse Plane ◽  
Phospholipid Bilayer ◽  
Cytochrome P 450

1. The phospholipid bilayer of intact vesicles from smooth endoplasmic reticulum is impermeable to macromolecules. Specific and non-specific proteinases were used to investigate the site of membrane proteins in the transverse plane of the bilayer. 2. When two proteinases were used in conjunction, denaturing effects additional to proteolysis were observed on cytochrome P-450 content and glucose 6-phosphatase activity which did not depend on the integrity of the phospholipid bilayer. 3. When lipid peroxidation was inhibited, these effects were not observed.

Anisopachous Cisternae and Cubic Lattice Structures in Hepatocytes of Rats Treated with Aminotriazole

1974 ◽  
Vol 32 ◽  
pp. 200-201
Author(s):  
Z. Hruban ◽  
A. Slesers ◽  
M. Gotoh
Keyword(s):  
Endoplasmic Reticulum ◽  
Smooth Endoplasmic Reticulum ◽  
Young Male ◽  
Chow Diet ◽  
Sprague Dawley ◽  
Metabolizing Enzymes ◽  
Cubic Lattice ◽  
Sprague Dawley Rats ◽  
Tubular Endoplasmic Reticulum ◽  
Stimulation Of

Administration of 3-amino-l,2,4-triazole (AT) decreases the activities of drug-metabolizing enzymes and inhibits the stimulation of the drugmetabolizing activities by the administration of phenobarbital (1). In the present study 1% AT in chow diet was fed ad libitum to young male Sprague-Dawley rats for 6 weeks. Thyroxin was given at 0, 0.5, 1.0, 1.5 and 2.0 ng per liter of drinking water. It was established that 1.0 mg thyroxin/L is adequate to prevent thyromegaly induced by AT.Rats fed AT alone or with 0.5% acetylsalicylic acid for 6 weeks showed alterations of the endoplasmic reticulum in their liver cells. The hepatocytes contained variable amounts of conglomerates of the tubular smooth endoplasmic reticulum (Figs. 8, 9), some of which were less than 0.5 micron in diameter (Figs. 5, 6). The anastomosing tubules were more closely packed and the intertubular spaces were narrower when compared with tubular endoplasmic reticulum of normal hepatocytes.

Effect of Adrenalectomy and of Adrenocortical Hormones on RNA Turnover in a Variety of Subcellular Fractions of Rat Liver

1973 ◽  
Vol 51 (6) ◽  
pp. 920-930 ◽  
Author(s):  
R. K. Mishra ◽  
L. A. W. Feltham
Keyword(s):  
Endoplasmic Reticulum ◽  
Steady State ◽  
Rat Liver ◽  
Orotic Acid ◽  
Turnover Rate ◽  
Single Injection ◽  
Smooth Endoplasmic Reticulum ◽  
Rna Turnover ◽  
Liver Nuclei ◽  
Adrenalectomized Rats

(1) The turnover of RNA was examined by following the loss of radioactivity after a single injection of 14C-orotic acid in nuclei, mitochondria, smooth endoplasmic reticulum, rough endoplasmic reticulum, free polysomes, total ribosomes, and sRNA from rat liver. The half-lives of the RNA of various rat liver fractions were found to be 8.7, 6.5, 6.4, 5.4, 4.4, 4.9, and 4.8 days, respectively.(2) In adrenalectomized rats there was a significant decrease in turnover rate. This suggests a slower synthesis of RNA under steady-state conditions. The corresponding values were 12.0, 8.5, 6.5, 6.9, 5.8, 6.1, and 5.9 days.(3) Daily administration of corticosterone or hydrocortisone to adrenalectomized rats restored the turnover rate to normal. Aldosterone was without effect.(4) Aggregate RNA polymerase of rat liver nuclei was decreased by adrenalectomy and restored by corticosterone or hydrocortisone. Aldosterone was without effect.

scholarly journals Asymmetric distribution of cytochrome P-450 and NADPH–cytochrome P-450 (cytochrome c) reductase in vesicles from smooth endoplasmic reticulum of rat liver

1980 ◽  
Vol 190 (3) ◽  
pp. 737-746 ◽  
Author(s):  
Michael B. Cooper ◽  
John A. Craft ◽  
Margaret R. Estall ◽  
Brian R. Rabin
Keyword(s):  
Endoplasmic Reticulum ◽  
Cytochrome C ◽  
Rat Liver ◽  
Smooth Endoplasmic Reticulum ◽  
Reductase Activity ◽  
Asymmetric Distribution ◽  
Trypsin Treatment ◽  
Cytochrome C Reductase ◽  
Nadph Cytochrome ◽  
Cytochrome P 450

1. The topography of cytochrome P-450 in vesicles from smooth endoplasmic reticulum of rat liver has been examined. Approx. 50% of the cytochrome is directly accessible to the action of trypsin in intact vesicles whereas the remainder is inaccessible and partitioned between luminal-facing or phospholipid-embedded loci. Analysis by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis reveals three major species of the cytochrome. Of these, the variant with a mol.wt. of 52000 is induced by phenobarbitone and this species is susceptible to trypsin. 2. After trypsin treatment of smooth membrane, some NADPH–cytochrome P-450 (cytochrome c) reductase activity remains and this remaining activity is enhanced by treatment with 0.05% deoxycholate, which renders the membranes permeable to macromolecules. In non-trypsin-treated control membranes the reductase activity is increased to a similar extent. These observations suggest an asymmetric distribution of NADPH–cytochrome P-450 (cytochrome c) reductase in the membrane. 3. As compared with dithionite, NADPH reduces only 44% of the cytochrome P-450 present in intact membranes. After tryptic digestion, none of the remaining cytochrome P-450 is reducible by NADPH. 4. In the presence of both a superoxide-generating system (xanthine plus xanthine oxidase) and NADPH, all the cytochrome P-450 in intact membrane (as judged by dithionite reducibility) is reduced. The cytochrome P-450 remaining after trypsin treatment of smooth vesicles cannot be reduced by this method. 5. The superoxide-dependent reduction of cytochrome P-450 is prevented by treatment of the membranes with mersalyl, which inhibits NADPH–cytochrome P-450 (cytochrome c) reductase. Thus the effect of superoxide may involve NADPH–cytochrome P-450 reductase and cytosolically orientated membrane factor(s).

scholarly journals Studies on selenium incorporation into, and electron-transfer function of, liver microsomal fractions from normal and vitamin E-deficient rats given phenobarbitone

1973 ◽  
Vol 136 (4) ◽  
pp. 851-858 ◽  
Author(s):  
Christine P. J. Caygill ◽  
A. T. Diplock ◽  
Elizabeth H. Jeffery
Keyword(s):  
Endoplasmic Reticulum ◽  
Electron Transfer ◽  
Vitamin E ◽  
Current Knowledge ◽  
Smooth Endoplasmic Reticulum ◽  
Active Centre ◽  
Protein X ◽  
Cytochrome P 450 ◽  
Haem Iron ◽  
Expected Increase

1. The incorporation of75Se from Na275SeO3 into the liver endoplasmic reticulum of rats given phenobarbitone was investigated by using a zonal centrifuge technique. 2. It was found that, in rats deprived of vitamin E, or of vitamin E and selenium, phenobarbitone was without effect on the incorporation of75Se or on its conversion to75Se2-. When vitamin E was given at the same time as the phenobarbitone and75Se, there was a large increase in the amount of75Se and75Se2-found in the smooth reticulum. It is concluded that there may be a specific vitamin E-dependent role for selenium and selenide in the smooth endoplasmic reticulum, and it is suggested, in the light of these and other observations, that the selenide may form a part of the active centre of a non-haem iron-containing protein ‘X‘, that may function in microsomal electron transport. 3. Measurements of the contents of cytochromes P-450 and b5 in liver microsomal fractions of rats given vitamin E-deficient, and vitamin E- and selenium-deficient diets, showed that haemoprotein biosynthesis is unimpaired in these rats and phenobarbitone treatment resulted in the expected increase in the haemoproteins. 4. When the reduction of cytochrome P-450 by NADH and NADPH was measured, no difference was found between normal and deficient animals. 5. These results are discussed in relation to current knowledge of microsomal electron transfer.

Sign in / Sign up

Export Citation Format

Share Document