Various forms of chemically induced liver injury and their detection by diagnostic procedures.
A large number of chemical agents, administered for therapeutic or diagnostic purposes, can produce various types of hepatic injury by several mechanisms. Some agents are intrinsically hepatotoxic, and others produce hepatic injury only in the rare, uniquely susceptible individual. Idiosyncrasy of the host is the mechanism for most types of drug-induced hepatic injury. It may reflect allergy to the drug or a metabolic aberation of the host permitting the accumulation of hepatotoxic metabolites. The syndromes of hepatic disease produced by drugs have been classified hepatocellular, hepatocanalicular, mixed and canalicular. Measurement of serum enzyme activities has provided a powerful tool for studies of hepatotoxicity. Their measurement requires awareness of relative specificity, knowledge of the mechanisms involved, and knowledge of the relationship between known hepatotoxic states and elevated enzyme activities. (+info)
The urinary elimination profiles of diazepam and its metabolites, nordiazepam, temazepam, and oxazepam, in the equine after a 10-mg intramuscular dose.
A method for the extraction of diazepam and its metabolites (nordiazepam, temazepam, and oxazepam) from equine urine and serum and their quantitation and confirmation by liquid chromatography-tandem mass spectrometry is presented. Valium, a formulation of diazepam, was administered at a dose of 10 mg intramuscularly to four standard-bred mares. Diazepam is extensively metabolized in the horse to nordiazepam, temazepam, and oxazepam. Diazepam urinary concentrations were found to be less than 6 ng/mL. Nordiazepam was found to be mainly in its glucuronide-conjugated form and was measured out to a collection time of 53-55 h. Oxazepam and temazepam were entirely conjugated, and their urinary concentrations were measured out to collection times of 121 h and 77-79 h, respectively. Diazepam and nordiazepam were measured in equine postadministration serum out to collection times of 6 and 54 h, respectively. Oxazepam and temazepam were not detected in postadministration serum. (+info)
Inhibition of transient and persistent Na+ current fractions by the new anticonvulsant topiramate.
The actions of the antiepileptic drug topiramate (TPM) on Na+ currents were assessed using whole-cell patch-clamp recordings in dissociated neocortical neurons and intracellular recordings in neocortical slices. Relatively low TPM concentrations (25-30 microM) slightly inhibited the persistent fraction of Na+ current in dissociated neurons and reduced the Na+-dependent long-lasting action potential shoulders, which can be evoked in layer V pyramidal neurons after Ca++ and K+ current blockade. Conversely, the same drug concentrations were ineffective in reducing the amplitude of the fast Na+-dependent action potentials evoked in slices or the peak of transient Na+ (INaf) current evoked in isolated neurons from a physiological holding potential. Consistent INaf inhibition became, however, evident only when the neuronal membrane was kept depolarized to enhance resting Na+ channel inactivation. TPM (100 microM) was ineffective on the voltage dependence of activation but induced a leftward shift of the steady-state INaf inactivation curve. The drug-induced inhibitory effect increased with the duration of membrane depolarization, and the recovery of INaf after long membrane depolarizations was slightly delayed in comparison with that observed under control conditions. The obtained evidence suggests that the anticonvulsant action of TPM may operate by stabilizing channel inactivation, which can be induced by depolarizing events similar to those occurring in chronic epileptic conditions. Concurrently, the slight but significant inhibition of the persistent fraction of the Na+ current, obtained with the application of relatively low TPM concentrations, may contribute toward its anticonvulsant effectiveness by modulating the near-threshold depolarizing events that are sustained by this small current fraction. (+info)
Inhibition of monoamine oxidase type A, but not type B, is an effective means of inducing anticonvulsant activity in the kindling model of epilepsy.
The anticonvulsant activity of inhibitors of monoamine oxidase (MAO) was reported early after the development of irreversible MAO inhibitors such as tranylcypromine, but was never clinically used because of the adverse effects of these compounds. The more recently developed reversible MAO inhibitors with selectivity for either the MAO-A or MAO-B isoenzyme forms have not been studied extensively in animal models of epilepsy, so it is not known which type of MAO inhibitor is particularly effective in this respect. We compared the following drugs in the kindling model of epilepsy: 1) L-deprenyl (selegiline), i.e., an irreversible inhibitor of MAO-B, which, however, also inhibits MAO-A at higher doses, 2) the novel reversible MAO-B inhibitor LU 53439 (3,4-dimethyl-7-(2-isopropyl-1,3, 4-thiadiazol-5-yl)-methoxy-coumarin), which is much more selective for MAO-B than L-deprenyl, 3) the novel reversible and highly selective MAO-A inhibitor LU 43839 (esuprone; 7-hydroxy-3, 4-dimethylcoumarin ethanesulfonate), and 4) the irreversible nonselective MAO inhibitor tranylcypromine. Esuprone proved to be an effective anticonvulsant in the kindling model with a similar potency as L-deprenyl. In contrast to esuprone and L-deprenyl, the selective MAO-B inhibitor LU 53439 was not effective in the kindling model; this substantiates the previous notion that the anticonvulsant activity of L-deprenyl is not related to MAO-B inhibition, but to other effects of this drug, such as inhibition of MAO-A. Drugs inhibiting both MAO-A and MAO-B to a similar extent (tranylcypromine) or combinations of selective MAO-A and MAO-B inhibitors (esuprone plus LU 53439) had no advantage over MAO-A inhibition alone, but were less well tolerated. The data thus suggest that selective MAO-A inhibitors such as esuprone may be an interesting new approach for the treatment of epilepsy. (+info)
Gabapentin suppresses ectopic nerve discharges and reverses allodynia in neuropathic rats.
Repetitive ectopic discharges from injured afferent nerves play an important role in initiation and maintenance of neuropathic pain. Gabapentin is effective for treatment of neuropathic pain but the sites and mechanisms of its antinociceptive actions remain uncertain. In the present study, we tested a hypothesis that therapeutic doses of gabapentin suppress ectopic afferent discharge activity generated from injured peripheral nerves. Mechanical allodynia, induced by partial ligation of the sciatic nerve in rats, was determined by application of von Frey filaments to the hindpaw. Single-unit afferent nerve activity was recorded proximal to the ligated sciatic nerve site. Intravenous gabapentin, in a range of 30 to 90 mg/kg, significantly attenuated allodynia in nerve-injured rats. Furthermore, gabapentin, in the same therapeutic dose range, dose-dependently inhibited the ectopic discharge activity of 15 injured sciatic afferent nerve fibers through an action on impulse generation. However, the conduction velocity and responses of 12 normal afferent fibers to mechanical stimulation were not affected by gabapentin. Therefore, this study provides electrophysiological evidence that gabapentin is capable of suppressing the ectopic discharge activity from injured peripheral nerves. This action may contribute, at least in part, to the antiallodynic effect of gabapentin on neuropathic pain. (+info)
Biochemical and electrophysiological studies on the mechanism of action of PNU-151774E, a novel antiepileptic compound.
PNU-151774E [(S)-(+)-2-(4-(3-fluorobenzyloxy)benzylamino)propanamide methanesulfonate], a new anticonvulsant that displays a wide therapeutic window, has a potency comparable or superior to that of most classic anticonvulsants. PNU-151774E is chemically unrelated to current antiepileptics. In animal seizure models it possesses a broad spectrum of action. In the present study, the action mechanism of PNU-151774E has been investigated using electrophysiological and biochemical assays. Binding studies performed with rat brain membranes show that PNU-151774E has high affinity for binding site 2 of the sodium channel receptor, which is greater than that of phenytoin or lamotrigine (IC50, 8 microM versus 47 and 185 microM, respectively). PNU-151774E reduces sustained repetitive firing in a use-dependent manner without modifying the first action potential in hippocampal cultured neurons. In the same preparation PNU-151774E inhibits tetrodotoxin-sensitive fast sodium currents and high voltage-activated calcium currents under voltage-clamp conditions. These electrophysiological activities of PNU-151774E correlate with its ability to inhibit veratrine and KCl-induced glutamate release in rat hippocampal slices (IC50, 56.4 and 185.5 microM, respectively) and calcium inward currents in mouse cortical neurons. On the other hand, PNU-151774E does not affect whole-cell gamma-aminobutryic acid- and glutamate-induced currents in cultured mouse cortical neurons. These results suggest that PNU-151774E exerts its anticonvulsant activity, at least in part, through inhibition of sodium and calcium channels, stabilizing neuronal membrane excitability and inhibiting transmitter release. The possible relevance of these pharmacological properties to its antiepileptic potential is discussed. (+info)
Effect of riluzole on the neurological and neuropathological changes in an animal model of cardiac arrest-induced movement disorder.
Posthypoxic myoclonus and seizures precipitate as secondary neurological consequences in ischemic/hypoxic insults of the central nervous system. Neuronal hyperexcitation may be due to excessive activation of glutamatergic neurotransmission, an effect that has been shown to follow ischemic/hypoxic events. Therefore, riluzole, an anticonvulsant that inhibits the release of glutamate by stabilizing the inactivated state of activated voltage-sensitive sodium channels, was tested for its antimyoclonic and neuroprotective properties in the cardiac arrest-induced animal model of posthypoxic myoclonus. Riluzole (4-12 mg/kg i.p.) dose-dependently attenuated the audiogenic seizures and action myoclonus seen in this animal model. Histological examination using Nissl staining and the novel Fluoro-Jade histochemistry in cardiac-arrested animals showed an extensive neuronal degeneration in the hippocampus and cerebellum. Riluzole treatment almost completely prevented the neuronal degeneration in these brain areas. The neuroprotective effect was more pronounced in hippocampal pyramidal neurons and cerebellar Purkinje cells. These effects were seen at therapeutically relevant doses of riluzole, and the animals tolerated the treatment well. These findings indicate that the pathogenesis of posthypoxic myoclonus and seizure may involve excessive activation of glutamate neurotransmission, and that riluzole may serve as an effective pharmacological agent with neuroprotective potential for the treatment of neurological conditions associated with cardiac arrest in humans. (+info)
Pharmacological studies on root bark of mulberry tree (Morus alba L.)
Pharmacological studies were done on the root bark of mulberry tree and pharmacological effects were compared with the clinical effects of "Sohakuhi" in Chinese medicine. n-Butanol- and water-soluble fractions of mulberry root had similar effects except for those on the cadiovascular system. Both fractions showed cathartic, analgesic, diuretic, antitussive, antiedema, sedative, anticonvulsant, and hypotensive actions in mice, rats, guinea pigs and dogs. There appears to be a correlation between the experimental pharmacological results and the clinical applications of mulberry root found in the literature on Chinese medicine. (+info)