In vitro effects of calcium channel blockers and beta-adrenergic blocking agents on microsomal lipid perocidation and cytochrome p-450 content.

The effects of the calcium channel blockers (CCB) nifedipine (N), verapamil (V) and diltiazem (D) and the beta adrenergic blocking agents (BAB) propranolol (P) and atenolol (A) administered alone or in combination on lipid peroxidation (LPO) and cytochrome p-450 content were studied in rat liver microsomes. The drugs were tested in concentrations of 1 mM. V, A and P alone significantly decreased TBARS formed after in vitro stimulation of LPO by Fe2+ and ascorbate, whereas no antioxidant effect was found for N and D. A correlation between the antioxidant capacity of the drugs and their ability to protect cytochrome p-450 after in vitro stimulation of LPO was observed except for propranolol. Moreover, propranolol abolished cytochrome p-450 protecting effect of verapamil when administered together. A direct, LPO-independent decreasing effect on cytochrome p-450 was observed upon in vitro incubation of microsomes with propranolol. The results are discussed in terms of LPO-dependent degradation of cytochrome p-450, formation of propranolol reactive metabolites and propranolol-dependent changes in cytochrome lipid environment.

Effect of multiple administration of calcium antagonists on lipid peroxidation in rat liver microsomes.

The effects of three calcium antagonists, nifedipine (NF), verapamil (VP), and diltiazem (DT), on the lipid peroxidation (LPO) in rat liver microsomes were studied. The drugs were administered in oral doses of 50, 40, and 30 mg/kg daily for 21 days in male Wistar rats. Nonstimulated LPO was significantly decreased by NF and was not changed by VP and DT. There was a correlation between the extent of the previously found enzyme-inducing action and the potency of the antioxidant effects of calcium antagonists. Fe2+/NADPH- and Fe2+/ascorbate-stimulated microsomal LPO was increased by the calcium antagonists studied in the following order: VP > DT > NF (the increase caused by NF was insignificant in Fe2+ NADPH stimulation).

An unusual temperature dependence of malondialdehyde formation in Fe2+/H2O2-initiated lipid peroxidation of phosphatidylcholine liposomes.

Determination of malondialdehyde is a widely used procedure for measurement of lipid peroxidation. In this paper we report an unusual temperature dependence of malondialdehyde formation in egg yolk phosphatidylcholine liposomes oxidized by the Fenton system (0.1 mmol/l FeSO4 and 0.05 mmol/l H2O2). The amount of malondialdehyde formed was 37% higher in samples kept at 22 degrees C than at 50 degrees C. An alternative method for determination of lipid peroxidation, measurement of oxygen uptake, revealed complete consumption of dissolved oxygen to peroxidized lipids at 22 degrees C as well as 50 degrees C. Since oxygen is essential for the formation of cyclic peroxides--precursors of malondialdehyde--we conclude that the nature of the observed effect consists in limitation of oxygen availability at elevated temperatures.

Role of iron ion chelation by quinones in their reduction, OH-radical generation and lipid peroxidation.

To study the role of the complex of quinones with iron ions in the processes of quinone reduction and OH-radical generation in the presence of ascorbate (AH) and glutathione (GSH) the quinone-chelators have been used: 2-phenyl-4-butylaminonaphtho[2,3-h]quinolindione-7,12 (Qc) and adriamycin (Adr). 2-Phenyl-5-nitronaphtho[2,3-g]indodione-6,11 (Qn), 2-(3-hydroxypropyl)anthraquinone (AQOP) and 2-dimethylamino-3-chlor-1,4-naphthoquinone (DCNQ) were chosen as quinones that do not chelate iron ions. It was found that, unlike Adr and nonchelating quinones Qn, AQOP, and DCNQ, addition of Qc to AH and GSH leads to semiquinone EPR spectrum formation and OH-radical generation via the complex of Qc with iron ions. It was demonstrated that all these quinones can be reduced by AH. However, reduction constant of Qc-Fe(3+) by the AH was 98 +/- 9 M-1c-1, while DCNQ reduction constant was only 0.042 +/- 0.005 M-1 c-1. It was found that in the presence of GSH only complexes of quinones Qc and Adr with iron ions are reduced. It is concluded that the capability of Qc to reduce and to generate OH-radicals is related to intramolecular electron transfer by the reaction: Fe(2+)-Qc<==>Fe(3+)-Qc. The capability Qc to increase generation of oxygen radicals and to inhibit lipid peroxidation may be interesting for designing quinone-containing antibiotics.

Influence of long-term treatment with the Ca2(+)-antagonists nifedipine, verapamil, flunarizine and with the calmodulin antagonist trifluoperazine on beta-adrenoceptors in rat cerebral cortex.

1. The binding of [3H] dihydroalprenolol ((3H]DHA) to beta-adrenoceptors in cerebral cortex membranes (fraction P2) was studied after 13-day oral treatment of male Wistar rats with the Ca2(+)-antagonists nifedipine (20 mg/kg), verapamil (50 mg/kg), flunarizine (10 mg/kg) and with the calmodulin (CaM)-antagonist trifluoperazine (TFP) (3 mg/kg). 2. A significant reduction in the number (Bmax) of binding sites for [3H]DHA was established after the 3 Ca2(+)-antagonists as well as after TFP. 3. No changes in the affinity values (Kd) [3H]DHA binding were found in all treated groups. 4. The fluidity characteristics of the cerebral cortex membranes in nifedipine- and flunarizine-treated rats did not differ from those in controls. 5. Based on these results, we concluded that long-term treatment with Ca2(+)- and calmodulin-antagonists might induce changes in the central adrenergic mechanisms.

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.

Comparative study of the anticonvulsive activity of N-aminomethylpiperazine-3,3-diethyl 2,4-pyridinedione with the activity of known antiepileptic agents.

N-aminomethylpiperazine-3,3-diethyl-2,4-pyridinedione (DKMP) is a newly synthesized compound with a marked anticonvulsive effect in various epileptic models. The aim of the present work is to compare its anticonvulsive effect in corazol convulsions (100 mg/kg corazol, s.c.) with known anticonvulsants applied in clinical practice. The compounds tested were applied subcutaneously in equitoxic doses (1/20 and 1/30 of their respective LD50). Some undesirable side effects of the antiepileptic agents tested were also studied. With the experimental model used, DKMP was found to have a better anticonvulsive effect compared with diphenylhydantoin, depakin, suxilep and phenobarbital. Diazepam completely inhibited the convulsions, but it has an undesirable strong myorelaxing effect. In a subchronical experiment it was found that no tolerance developed toward DKMP, while the anticonvulsant effect of diazepam significantly decreased on the 15th day, compared with a single administration. Using the rota-rod test it was found that the agents studied had a stronger neurotoxic action compared with DKMP. These results outline DKMP as a promising compound with good antiepileptic activity, comparable to that of the known anticonvulsants.