Combined effect of propranolol with nifedipine or with diltiazem on rat liver monooxygenase activities.

The effects of two Ca2+ antagonists nifedipine (NF) and diltiazem (DL) and of the nonselective beta-adrenergic blocking agent propranolol (PR) on the hexobarbital (HB) sleeping time and on the activity of some liver drug-metabolizing enzyme systems in male Wistar rats were studied. Two h after single oral administration PR (50 mg/kg) did not change HB sleeping time, while NF (50 mg/kg) and DL (30 mg/kg) prolonged it by 171.2 and 99.6%, respectively. Coadmistration of PR with DL or with NF significantly prolonged HB sleep by 240.7 and 129%, respectively. Only NF increased aniline 4-hidroxylase (AH) activity (by 92%) and the total P-450 content (by 24%). PR and NF increased cytochrome b5 content and this effect was also observed with the combinations PR + NF (by 109%) and PR + DL (by 102%). The NADPH cytochrome P-450 reductase activity was significantly decreased by NF and DL and after their combination with PR. The ethymorphine-N-demethylase (EMND) and amidopyrine-N-demethylase (APND) activities were not changed. The effects of PR, NF and DL administrated alone or in combination on liver oxidative metabolism are considered as possible mechanisms of drug interactions.

Interaction of dexamethasone with acetylsalicylic acid in mice.

The effect of acetylsalicylic acid (ASA, 160 mg/kg b.wt.) and dexamethasone (DEX, 15 mg/kg b.wt.) on ASA antinociception and toxicity when administered orally alone or in combination for 4 consecutive days was studied in male albino mice. ASA antinociception decreased after repeated ASA administration. Bleeding time was prolonged and the intestinal ASA esterase activity was increased, which was probably related to the increased ASA general toxicity in ASA-treated animals. There were no changes in the blood alkaline content, in the ulcerogenic or hepatotoxic effect of ASA, nor in the hepatic monooxygenase activity (ethylmorphine N-demethylase and aniline hydroxylase and the cytochrome P450 and b-5 content). DEX administered alone exerted a significant antinociceptive effect, increased both acute ASA toxicity and aniline hydroxylase activity and decreased body growth. However, DEX did not change the bleeding time, the alkaline blood content nor the intestinal esterase activity. The combination of ASA and DEX did not increase the ASA antinociceptive effect nor the general and specific toxicity of ASA. DEX in combination even abolished the effect of ASA on intestinal ASA esterase and on bleeding time. DEX also increased the hepatic cytochrome P450 content and did not change the ulcerogenic effect of ASA nor the alkaline blood content.

Influence of hydrocortisone on the analgesic effect, toxicity and metabolism of aspirin in mice.

1. Hydrocortisone (HC; 80 mg/kg body weight, intraperitoneally for 4 days), both alone and in combination with acetylsalicylic acid (ASA; 160 mg/kg body weight, orally, for 4 days), decreased ASA general and specific toxicity via metabolic modulation of drug-metabolizing enzyme systems (intestinal ASA-esterase and hepatic UDP-glucuronyltransferase) and did not change the ASA analgesic effect. 2. ASA alone, given 4 for days, did not change the specific ASA toxicity, but increased its general acute toxicity, which was probably due to alterations in some intestinal and hepatic metabolizing enzyme systems.

Effects of acetysal, dexamethasone and their combination on drug metabolizing enzyme systems in rat liver microsomes.

After 4 days of acetysal treatment (160 mg/kg body weight orally), the following were established: a higher acute toxicity of acetysal, an inducing effect on amidopyrin N-demethylase and analgin N-demethylase activity and increases in cytochrome P-450 and cytochrome b5 content. Aniline hydroxylase activity decreased, thiopental sleeping time was prolonged and UDP-glucuronyltransferase activity was not changed. Dexamethasone, at a dose of 5 mg/kg body weight p.o. for 4 days, did not change acetysal acute toxicity but at a dose of 100 mg/kg i.p. increased it. Thiopental sleeping time was shortened by dexamethasone (100 mg/kg i.p.) but was not changed by dexamethasone at 5 mg/kg p.o., alone or in combination. Dexamethasone at 5 mg/kg increased analgin N-demethylase and UDP-glucuronyltransferase activities, did not change cytochrome P-450 content and decreased aniline hydroxylase activity. The combination with 5 mg/kg dexamethasone increased the activity of amidopyrin N-demethylase, analgin N-demethylase and UDP-glucuronyltransferase and decreased those of amitriptyllin N-demethylase and aniline hydroxylase and cytochrome P-450 content. Ethylmorphine N-demethylase, benzphetamine N-demethylase, NADPH-cytochrome c reductase and glutathione S-transferase activities were not affected significantly by acetysal, dexamethasone or their combination. Hepatic carboxyl esterase was depressed by dexamethasone (5 mg/kg) and was increased by the combination. Lipid peroxidation was not changed by dexamethasone (5 mg/kg) but was decreased by acetysal and the combination.

Liver enzyme activities after multiple administration of nifedipine in mice.

The effect of multiple nifedipine administration on hexobarbital sleeping time, liver monooxygenase and synthetase activities, lipid peroxidation and microsomal membrane fluidity were studied in male albino mice. The drug was administered orally at a dose of 25 mg/kg daily for 14 and 21 days. Nifedipine caused enzyme induction, demonstrated by shortened hexobarbital sleeping time, enhanced ethylmorphine N-demethylase, aniline 4-hydroxylase, ethoxycoumarine O-deethylase, UDP-glucuronyl transferase, glutathione S-transferase and NADPH-cytochrome c reductase activities and increased content of cytochrome P450 and cytochrome b5. This effect persisted until the 7th day after the last dose of nifedipine. There were no changes in lipid peroxidation and fluidity of the microsomal membranes after 14-day nifedipine administration. The increased cytochrome P450 content and drug metabolizing enzyme activities could be not associated with changes in these liver microsomal membrane properties.

Influence of rifampicin on the toxicity and the analgesic effect of acetaminophen.

The influence of rifampicin on the toxicity, analgesic effect and pharmacokinetics of acetaminophen was studied in male albino mice. Repeated administration of rifampicin (50 mg/kg i.p. daily for 6 days) shortened hexobarbital sleeping time and increased liver weight, microsomal cytochrome P-450 and heme contents, NADPH-cytochrome c reductase and ethylmorphine-N-demethylase activities. Aniline hydroxylase activity was decreased and glucuronidation of p-nitrophenol was unaffected. Rifampicin pretreatment changed neither the LD50 of acetaminophen nor the hepatic glutathione level nor the glutathione depletion provoked by the toxic dose of acetaminophen (737 mg/kg p.o.). This suggests that rifampicin has no influence on the amount of acetaminophen toxic metabolites formed in the liver. Rifampicin decreased the acetaminophen analgesic effect in mice. Rifampicin decreased the Cmax, the half-time, the MRT and the AUC of acetaminophen and accelerated its clearance. The plasma concentration of acetaminophen glucuronide and acetaminophen sulfate was increased. It is assumed that the most probable mechanism by which rifampicin decreases acetaminophen analgesia is the accelerated acetaminophen elimination.

On the enzyme-inducing action of calcium antagonists.

The effects of three calcium antagonists, nifedipine (NF), verapamil (V) and diltiazem (DL), on rat liver monooxygenases were studied. The drugs were administered in oral doses of 50, 40 and 30 mg/kg daily for 3 weeks in male Wistar rats. NF and V shortened the hexobarbital (HB) sleeping time and increased benzphetamin-N-demethylase (BND), ethylmorphine-N-demethylase (EMND), aniline hydroxylase (AH), ethoxycoumarine-O-deethylase (ECOD), ethoxyresorufin-O-deethylase (EROD) and NADPH-cytochrome c reductase activities and the content of cytochrome P-450 and microsomal heme, but did not change the content of cytochrome b5. The data suggest that these calcium antagonists exert an enzyme-inducing effect on the hepatic monooxygenases. DL significantly increased only the EROD and NADPH-cytochrome c reductase activities and shortened HB sleeping time to a lesser extent, suggesting a weaker enzyme-inducing effect as compared to NF and V. The three drugs increased the delta-aminolevulinic acid (ALA) synthetase activity and decreased heme oxygenase (HO) activity. The increased cytochrome P-450 content is probably due to the increased synthesis and the decreased breakdown of this hemoprotein.

Effects of propranolol, pindolol and atenolol after multiple administration in rats on the duration of hexobarbital sleeping time and on the activity of some drug-metabolizing enzyme systems.

Three beta-adrenergic blocking agents propranolol (50 mg/kg), pindolol (5mg/kg) and atenolol (150mg/kg) were administered orally in rats for 21 days. The duration of hexobarbital (HB) sleeping time and the activities of some liver monooxygenases and synthetases were studied. The HB sleeping time was not changed. Propranolol and pindolol decreased the ethylmorfin-N-demethylase (EMND) and benzphetamine-N-demethylase (BND) activities. The three beta-adrenergic blocking agents did not change the activities of anilinehydroxylase (AH), ethoxycoumarine-O-demethylase (ECOD), and glutathione-S-transferase (G-S-T), the total content of cytochrome P-450, b5 and microsomal heme. They increased the activities of uridinediphosphoglucuronil transferase (UDPGT) and NADPH-cytochrome C reductase. The participation of different mechanisms of the effects of the three beta-adrenergic blocking agents on the activity of drug-metabolizing enzyme systems was discussed.

Combined effect of fascioliasis and diethylnitrosamine carcinogenesis on the activity of the rat liver monooxygenase system.

1. The activity of the rat liver monooxygenase system after single and combined treatment with Fasciola hepatica and diethylnitrosamine (DENA) has been studied in a 27-week experiment. 2. The changes in lever drug metabolism were due mainly to F. hepatica with DENA having a modulating effect only. 3. The results are discussed with reference to earlier data of ours concerning the effects of stimulation or inhibition of DENA-induced liver carcinogenesis against a background of acute or chronic fascioliasis.

Induction of cytochrome P-450 isozymes upon repeated administration of nifedipine.

In experiments on male Wistar rats it has been found that nifedipine administration at a dose of 10 mg/kg body weight i.p. daily for 20 days did not significantly increase the total amount of cytochrome P-450 but markedly increased the 7 alpha-, 16 beta- and 6 beta-hydroxylation of androstenedione in liver microsomes, suggesting the induction of cytochromes P-450IIA1, P-450IIB1, and P-450IIIA1, respectively. The induction of cytochrome P-450IIIB1 was also confirmed immunochemically with polyclonal antibodies against cytochrome P-450IIB1/B2.

Effect of continuous treatment with some heavy metal salts upon rat hepatic monooxygenases.

The effect of 90-days treatment with Co(NO3)2, NiSO4, CdSO4, ZnSO4 and HgCL2 on the rat liver cytochrome P-450 linked monooxygenases was studied. It was found that all metal salts studied significantly decreased the activity of ethylmorphine N-demethylase in the rat liver. The activity of benzphetamine N-demethylase was decreased by the salts of Co, Cd and Zn whereas Hg and Ni did not change it. Hepatic microsomal cytochrome P-450 content was significantly decreased after treatment with Co, Cd, Zn and Ni and was not changed by Hg. Microsomal hem content was decreased by Co, Cd and Zn and was not changed by Ni and Hg. Co, Cd, Zn and Ni salts decreased the activity of 5-aminolevulinic acid synthetase which shows that the decreased cytochrome P-450 content was probably due to a decrease of its synthesis. HgCL2 had no enzyme inhibitory effect. All metal salts did not change the metabolizing activity of aniline hydroxylase which confirm that multiple molecule species of cytochrome P-450 exist in the liver of adult rats. The hepatic cytochrome b5 content was not changed by the metal salts studied which shows that probably cytochrome b5 was not involved in the enzyme inhibitory action of heavy metal salts on the rat liver monooxygenases.

Mechanisms of stabilization of biomembranes by alpha-tocopherol. The role of the hydrocarbon chain in the inhibition of lipid peroxidation.

The effects of alpha-tocopherol and its homologues with different chain lengths (6-hydroxy-chromanes: C1, C6, C11) on lipid peroxidation in natural membranes (liver microsomes and mitochondria, brain synaptosomes) and liposomes were studied. It was shown that the antioxidant activity of alpha-tocopherol homologues decreased in the order: C1 greater than C6 greater than C11 greater than alpha-tocopherol (C16). Using fluorescent measurements, the possible reasons underlying these differences were investigated: (i) the distribution between the aqueous media and nonpolar phase of the membrane, which predetermines the binding of alpha-tocopherol homologues to membranes; (ii) the incorporation of alpha-tocopherol homologues into lipid bilayer; (iii) non-uniform distribution (formation of the clusters) of tocopherol homologues in the lipid bilayer; and (iv) transbilayer mobility of alpha-tocopherol homologues and accessibility of the inhibitors for radical-generating centres under enzymically and non-enzymically induced lipid peroxidation. It was demonstrated that: (i) binding of C1 with membranes was less efficient than that of longer-chain homologues (C6, C11, C16); (ii) the level of incorporation of alpha-tocopherol homologues into membranes decreased in a succession alpha-tocopherol C11 greater than C6 greater than C1; (iii) all alpha-tocopherol homologues existed in the lipid bilayer not only in a monomeric form but also associated in clusters thus decreasing the efficiency of radical scavenging; (iv) the short-chain alpha-tocopherol homologue, C1, exhibited a high transbilayer mobility whereas the long-chain one, C16, underwent no transbilayer migration within tens of minutes. The inhibiting effect of alpha-tocopherol esters and C1-acetate was predetermined by their hydrolysis in biomembranes; a strong correlation exists between the rate of the ester hydrolysis and their antioxidant activity in the membrane. In liposomes, in which the esterase activity was absent, alpha-tocopherol esters and C1-acetate exhibited very low lipid peroxidation inhibition.

Antioxidant action of ubiquinol homologues with different isoprenoid chain length in biomembranes.

Ubiquinones (CoQn) are intrinsic lipid components of many membranes. Besides their role in electron-transfer reactions they may act as free radical scavengers, yet their antioxidant function has received relatively little study. The efficiency of ubiquinols of varying isoprenoid chain length (from Q0 to Q10) in preventing (Fe2+ + ascorbate)-dependent or (Fe2+ + NADPH)-dependent lipid peroxidation was investigated in rat liver microsomes and brain synaptosomes and mitochondria. Ubiquinols, the reduced forms of CoQn, possess much greater antioxidant activity than the oxidized ubiquinone forms. In homogenous solution the radical scavenging activity of ubiquinol homologues does not depend on the length of their isoprenoid chain. However in membranes ubiquinols with short isoprenoid chains (Q1-Q4) are much more potent inhibitors of lipid peroxidation than the longer chain homologues (Q5-Q10). It is found that: i) the inhibitory action, that is, antioxidant efficiency of short-chain ubiquinols decreases in order Q1 greater than Q2 greater than Q3 greater than Q4; ii) the antioxidant efficiency of long-chain ubiquinols is only slightly dependent on their concentrations in the order Q5 greater than Q6 greater than Q7 greater than Q8 greater than Q9 greater than Q10 and iii) the antioxidant efficiency of Q0 is markedly less than that of other homologues. Interaction of ubiquinols with oxygen radicals was followed by their effects on luminol-activated chemiluminescence. Ubiquinols Q1-Q4 at 0.1 mM completely inhibit the luminol-activated NADPH-dependent chemiluminescent response of microsomes, while homologues Q6-Q10 exert no effect. In contrast to ubiquinol Q10 (ubiquinone Q10) ubiquinone Q1 synergistically enhances NADPH-dependent regeneration of endogenous vitamin E in microsomes thus providing for higher antioxidant protection against lipid peroxidation. The differences in the antioxidant potency of ubiquinols in membranes are suggested to result from differences in partitioning into membranes, intramembrane mobility and non-uniform distribution of ubiquinols resulting in differing efficiency of interaction with oxygen and lipid radicals as well as different efficiency of ubiquinols in regeneration of endogenous vitamin E.

Effect of subchronic treatment with some heavy metal salts on the activity of the drug metabolizing enzyme system in female rats.

In experiments on female albino rats the effect of 30-day treatment with salts of Co, Cd, Ni, Zn and Hg on the liver monooxygenase system was studied. It was found that CdCl2 and HgCl2 significantly decreased the activity of aniline hydroxylase whereas the activity of ethylmorphine-N-demethylase tended to remain almost constant and no significant changes were observed. The cytochrome P-450 level in Zn-treated female rats was decreased while the other metal salts did not change it. The cytochrome b5 levels were relatively stable and there were no significant differences between treated and untreated animals. Co, Cd and Hg decreased the NADPH-dependent lipid peroxidation whereas Ni and Zn did not change it. All metal salts caused no marked alterations in the female rat liver microsomal membrane fluidity.

Liver monooxygenase activity after multiple application of nifedipin, verapamil and diltiazem.

The effects of three calcium antagonists--nifedipin (NF), verapamil (V) and diltiazem (DL)--on the duration of hexobarbital (HB) sleeping time and on monooxygenase activity are studied. The drugs are applied in oral doses of 50, 40 and 30 mg/kg, respectively every day for 3 weeks on male albino rats. NF was found to shorten the duration of HB sleep, to increase the activities of EMD, BPD, AH, ECOD, EROD, NADPH-cytochtome P-450 reductase and the content of cytochrome P-450, and it does not change significantly the content of cytochrome b 5. It increases AD hydroxylation in positions 7-alpha-, 16-beta-, 16-alpha- and 6-beta, which suggests indirectly that NF has probably induced the synthesis of cytochrome P-450a, cytochrome P-450b, cytochrome P-450h and cytochrome P-450p, respectively. Verapamil also shortens the duration of HB sleeping time, increases the activities of EMD, BPD, AH, EROD and NADPH-cytochrome P-450 reductase, not changing the cytochrome P-450 content and the ECOD activity. It increases AD hydroxylation in positions 7-alpha- and 16-alpha-, which suggests probable induction of the synthesis of cytochrome P-450a and cytochrome P-450h. Unlike the other two calcium antagonists, diltiazem slightly shortens the duration of HB sleeping, not changing the enzyme activities studied, the content of cytochrome P-450 and cytochrome b 5, but increases the activities of EROD and NADPH-cytocrome P-450 reductase. It increases AD hydroxylation in positions 7-alpha-, 16-alpha- and 6-beta, which suggests probable induction of cytochrome P-450a, cytochrome P-450h and cytochrome P-450p.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of potassium ethylxanthogenate on the acetaminophen hepatotoxicity in mice.

The effects of potassium ethylxanthogenate (PEX), acetaminophen (AAP) and their combination on the activity of serum transaminases, liver glutathione level and the activity of some drug metabolizing enzyme systems in male albino mice are studied. PEX (80 mg/kg p. o.), applied one hour before AAP (737.5 mg/kg p. o.) or simultaneously with it, prevents the AAP-induced rise in transaminases. PEX reduces significantly the AAP-induced depletion of the liver glutathione. Eighteen hours after the administration of a hepatotoxic dose of AAP, there is a statistically significant decrease of the activity of aniline hydroxylase, ethylmorphine demethylase, uridine diphosphoglucuronyl transferase, glutathione-S-transferase, NADPH-cytochrome-c-reductase, the P-450 content and a 5-fold increase of TBA-reactive products. PEX, introduced one hour before AAP or simultaneously with it, prevents these changes. The basic mechanism through which PEX reduces the liver toxicity of AAP is assumed to be the decrease in the amount of toxic metabolite formed.

The effect of alloxan diabetes on the activity of some mixed function oxidases in male rats.

The effect of alloxan-induced diabetes on the duration of hexobarbital sleep (HB sleep) the activity of ethylmorphine-N-demethylase (EMND), aniline hydroxylase (AH), the content of microsomal cytochrome P-450 and b5, on the activity of ethoxycumarine-0-deethylase (ECOD) and ethoxyresorufine-0-deethylase (EROD) after induction with beta naphthoflavone (beta-NF), as well as the activity of benzphetamine-N-demethylase and pentoxyresorufine-O-dealkylase (PROD) after induction with phenobarbital (PB), was studied in experiments on male Wistar rats. In rats with alloxan diabetes there was a significant prolongation of HB sleep (by 106%) and inhibition of the liver EMND (by 54%), while the AH activity increased by 131%, with a parallel rise in the content of microsomal cytochromes P-450 (by 67%) and b5 (by 113%). In rats with alloxan diabetes the enzyme-inducing effect of beta-NF with respect to the activities of EROD and ECOD is reduced, although diabetes by itself causes a rise in the ECOD activity in untreated animals. When induced with PB, the PROD and benzphetamine-N-demethylase activity in diabetic rats is lower than in the healthy animals. However, if the enzyme activity after the application of inducers is referred to the respective starting enzyme activities of the two groups of animals, it is found that the enzyme-inducing effect of PB is preserved and even slightly potentiated in the diabetic rats compared with the healthy ones: the increases in the benzphetamine-N-demethylase activity is by 60% in the diabetic rats, compared with a rise of 28% in the healthy animals, of the PROD activity 19 times for the diabetic compared with 16 times increase for the healthy rats.

Lipid peroxidation activation and cytochrome P-450 decrease in rat liver endoplasmic reticulum under oxidative stress.

Iron loading was associated with development of oxidative stress, viz, decrease in tocopherol content and an increase in amount of lipid peroxidation products but only slight, if any, decrease in cytochrome P-450 content. Combinations of iron loading with other stress-inducing treatments (exhaustive physical exercise and hyperoxia) caused marked decreases in cytochrome P-450 content. Thus, a combination of factors favoring development of oxidative stress, but insufficient to exert a damaging effect on the cytochrome P-450-dependent detoxification system when acting alone, may become quite potent when acting in concert.