Effects of energy and/or protein restriction on hepatic microsomal mixed function oxidase in male broiler chicks

1. Effect of energy and/or protein intake on a mixed function oxidase system (MFO) in hepatic microsomes was studied in male broiler chicks. 2. Contents of cytochrome P-450 and b5 in 72 hr starvation were larger than those in 12 and 36 hr starvations. 3. Reduction of energy and protein intake did not change the MFO, except cytochrome P-450. 4. Reduction of energy intake under the same protein intake increased the cytochrome P-450 content and aminopyrine N-demethylase activity. An increase in protein intake under the same energy intake also increased the cytochrome P-450 content.     

Differential localization of microsomal mixed function oxidase activity in periportal and perivenous hepatocytes isolated from rat liver

1. The activity per mg of microsomal protein of aminopyrine N-demethylase was higher in perivenous (PV) than in periportal (PP) hepatocytes of rat, but when it was expressed per cytochrome P-450 content the difference in the activity was not significant. 2. The activity of 7-ethoxycoumarin O-deethylase, when expressed per mg protein and per P-450 content, was significantly higher in PV than in PP cells. 3. The activities of dimethylnitrosamine(DMNA) N-demethylase and aniline p-hydroxylase were not significantly different between two subpopulations of isolated hepatocytes when either expressed per mg protein or per P-450 content.     

Induction of mixed function oxidases on oral administration of dieldrin

The administration of dieldrin (30 mg/kg body weight) caused an increase in the liver weight of rats. The metabolism of aflatoxins B₁ and G₁ by the microsomes obtained from the liver of dieldrin-treated animals was enhanced significantly as compared to the controls showing that dieldrin increased the activity of mixed function hydroxylases. Dieldrin caused an increase in the activity of liver microsomal NADPH oxidase and a decrease in the lipid peroxidation. Dieldrin brought about an increase in the phosphatidylcholine content of rat liver.     

The effect of allyl compounds on hepatic microsomal mixed function oxidation and porphyrogenesis.

The activities of 5-aminolaevulinate (5-ALA) synthetase and of various microsomat drug-metabolising enzymes have been determined in the livers of rats pretreated with different drugs and chemicals containing the allyl group. Safrole, isosafrole and secobarbital gave rise to slight increases in 5-ALA synthetase, whereas alclophenac and triallyl cyanurate almost doubled the enzyme activity and the known porphyrogenic agents, allylisopropylacetamide (AIA) and allobarbital caused increases of 1.5- and 2.5-fold, respectively. Allobarbital induced the microsomal drug-metabolising enzymes while secobarbital had only a weak effect and alclophenac and triallyl cyanurate had no effect at all. From these results it is suggested that induction of the synthesis of cytochrome P-450 is not rate dependent on the synthesis haem and induction of porphyrin biosynthesis.     

Brief maternal deprivation of rats reduces hepatic mixed function oxidase activities

Deprivation of pups from mother and sibs for 3 min daily from day 5 to day 41 of life reduced activities of 4 hepatic mixed function oxidases (MFO) expressed per mg protein in male rats compared to unhandled control rats. These decreases, though generally small, 22.4% and under, reached statistical significance for the substrates aminopyrine, benzphetamine and ethoxycoumarin. This handling procedure did not consistently affect the inductive response to phenobarbital. Previously ignored as a source of variability in response to xenobiotics, "handling" appears from these results to merit further investigation as such a factor in uninduced rats. Differences among rats in "handling" could contribute to large day-to-day variations in their metabolism of xenobiotics.     

The cryptic nature of hepatic microsomal sulphite oxidase

1. The activity of rat liver microsomal sulphite oxidase (EC 1.8.3.1) was increased several-fold on aging of microsomes, on delipidation by extraction with acetone or on solubilization with deoxycholate, suggesting its existence in a cryptic state. 2. In rat liver most of the sulphite oxidase was present in the nuclear fraction and only a small portion in the microsomes. 3. Microsomal sulphite oxidase activity was low in the developing embryo and increased rapidly after birth.     

Sex-related differences of hepatic microsomal mixed function oxidase system and antibody production in broilers implanted with corticosterone and/or fed ascorbic acid

1. Most of the components of the mixed function oxidase (MFO) in hepatic microsomes were reduced by corticosterone implants, and the degree of the reduction in females and at an older age was greater than those in males and at a younger age.2. Ascorbic acid (AA) prevented the reduction in the MFO caused by corticosterone implants.3. The activities of aniline hydroxylase and aminopyrine N-demethylase were enhanced by corticosterone implants regardless of AA supplementation.4. The activity of NADPH-cytochrome c reductase in male broiler was greater than that in females under normal conditions.5. Corticosterone implants and dietary AA had less influence on the antibody production, especially to T-cell dependent antigen.     

Stimulation of hepatic and renal diamine oxidase activity after acute ethanol administration

The effect of a single administration of ethanol (2 g/kg body weight) on hepatic and renal diamine oxidase activity was studied in fasted rats. Diamine oxidase activity significantly increased in liver and kidney 6 h after ethanol intubation. Pyrazole (an inhibitor of alcohol dehydrogenase), cycloheximide or actinomycin D (inhibitors of macromolecular syntheses), as well as prior adrenalectomy, prevented the ethanol-induced stimulation of diamine oxidase in the liver, but not in the kidney. The results demonstrated that the enhancement of diamine oxidase activity in the liver was due to an enzyme induction mediated by alcohol metabolism as well as by adrenals. In contrast, the stimulation of diamine oxidase activity in the kidney did not depend on synthesis of new enzyme molecules and was not mediated by ethanol metabolism or adrenal hormones.     

Studies on the microsomal mixed function oxidase system: redox properties of detergent-solubilized NADPH-cytochrome P-450 reductase.

Hepatic microsomal NADPH-cytochrome P-450 reductase was solubilized from rabbit liver microsomes in the presence of detergents and purified to homogeneity by column chromatography. The purified reductase had a molecular weight of 78 000 and contained 1 mol each of FAD and FMN per mol of enzyme. On reduction with NADPH in the presence of molecular oxygen, an 02-stable semiquinone containing one flavin free radical per two flavins was formed, in agreement with previous work on purified trypsin-solubilized reductase. The reduction of oxidized enzyme by NADPH, and autoxidation of NADPH-reduced enzyme by air, proceeded by both one-electron equivalent and two-electron equivalent mechanisms. The reductase reduced cytochrome P-450 (from phenobarbital-treated rabbits) and cytochrome P-448 (from 3-methylcholanthrene-treated rabbits). The rate of reduction of cytochrome P-450 increased in the presence of a substrate, benzphetamine, but that of cytochrome P-448 did not.     

Proliferative response and renewal of hepatic function following cocaine administration in mice

Experiments were undertaken to investigate the hepatic, temporal and spatial sequence of events following a single injection of cocaine, a known hepatotoxin. Centrilobular necrosis was induced in male mice (DBA/2Ha) 24 hr post-injection (PI). The time course of hepatic damage was monitored by assaying microsomal cytochrome P450 content, the activity of microsomal FAD-containing monooxygenase (FAD-M) and by determining the levels of serum glutamic pyruvic transaminase (SGPT). Kinetics of the onset of DNA synthesis were determined by autoradiography of thin liver sections and the incorporation of 3H-methyl thymidine into perchloric-acid-precipitable material. There was no increase in the labelling index (LI) and thymidine (TdR) incorporation in the first 24 hr PI. The LI rose to 14.6% and TdR incorporation showed a 5-fold increase over control values 48 hr PI. Both indices declined slightly at 72 hr PI and returned to control values by 96 hr PI. In contrast, the cytochrome P450 content declined by 69%, the FAD-M activity dropped by 40% and the SGPT levels showed an 18-fold increase at 24 hr PI, coincident with cytological signs of necrosis. Although the patterns of recovery differed between these selected enzymes, normal values were attained by 96 hr PI. These results demonstrate that cell damage and hepatic dysfunction precede the onset of DNA synthesis and subsequent proliferation.