Showing papers in "Pharmacology & Toxicology in 1995"

Adenosine, Adenosine Receptors and the Actions of Caffeine

Abstract: Of the known biochemical actions of caffeine, only inhibition of adenosine receptors occurs at concentrations achieved during normal human consumption of the drug. Under normal physiological conditions, adenosine is present in sufficient concentrations to activate A1 and A2a receptors. Via actions on A, receptors, adenosine decreases neuronal firing and the release of neurotransmitters. The exact mechanisms are not known, but several possibilities are discussed. Via actions on A2a receptors, adenosine - and hence caffeine - can influence dopaminergic neurotransmission. Caffeine can induce rapid changes in gene expression and, somewhat later, marked adaptive changes. These include antiepileptic and neuroprotective changes. Thus, caffeine has a number of central effects directly or indirectly related to adenosine receptors. Some of these are potentially useful, and drug development based on the actions of caffeine should be interesting.

Mechanism of cisplatin ototoxicity: antioxidant system.

Abstract: The dose and duration limiting toxic effects of cisplatin are ototoxicity and nephrotoxicity. While several studies have attempted to shed some light on the causes of nephrotoxicity, the reasons for ototoxicity induced by cisplatin are poorly understood. Therefore, this investigation was undertaken to delineate the potential mechanisms underlying cisplatin ototoxicity. The role of glutathione (GSH), oxidized glutathione (GSSG) and malondialdehyde levels, and antioxidant enzyme activities [superoxide dismutase, catalase, GSH peroxidase, and GSH reductase] were examined in cochlear toxicity following an acute dose of cisplatin. Male Wistar rats were treated with various doses of cisplatin. Pretreatment auditory brain stem evoked responses (ABR) were performed and then post-treatment ABRs and endocochlear potentials were also performed after three days. Acute cochlear toxicity (ototoxicity) was evidenced as elevated hearing thresholds and prolonged wave I latencies in response to various stimuli (clicks and tone bursts at 2, 8, 16 and 32 kHz) on ABRs. The endocochlear potentials were reduced (50% control) in cisplatin-treated rats as compared to control animals. The rats were sacrificed and cochleae isolated. The GSH, GSSG and malondialdehyde levels, and antioxidant enzyme activities were determined. Cisplatin ototoxicity correlated with a decrease in cochlear GSH [0.45 +/- 0.012 nmol/mg] after cisplatin administration compared to 0.95-012 nmol/mg in control cochleae (P < 0.05). Superoxide dismutase, catalase activities and malondialdehyde levels were significantly increased in the cochleae of cisplatin injected rats. Cochlear GSH-peroxidase and GSH reductase activity significantly decreased after cisplatin administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of the chiral forms of ketamine with opioid, phencyclidine, σ and muscarinic receptors

Abstract: In order to elucidate the mechanisms of action of ketamine, we have investigated the binding of the chiral forms of ketamine to opioid (mu, delta and kappa), phencyclidine, sigma and muscarinic receptors and we have performed detailed concentration-response experiments in the guinea-pig ileum preparation. The affinity ratios for the chiral forms at phencyclidine, mu and kappa receptors correlated with the potency ratio of the chiral forms in the ischaemic pain test found previously. The affinities were highest for phencyclidine receptors. The affinities for muscarinic receptors were lower than for phencyclidine receptors by a factor of about 10-20. The concentration-response experiments revealed one opioid (naloxone sensitive) and one non-opioid component. The two component are very close, which explains why other authors have reported that naloxone antagonizes the ketamine effect only partly. The concentrations of naloxone necessary to shift the opioid part of the curves indicate that ketamine is a kappa agonist in the guinea-pig ileum preparation. We conclude that the analgesic effect of ketamine in humans is most probably mediated via phencyclidine receptors, although a kappa effect can not be excluded. Binding to kappa and muscarinic receptors may contribute to the psychotomimetic side effects seen during recovery from ketamine anaesthesia.

Purinoceptors in the Nervous System

Abstract: The purine nucleoside adenosine and the purine nucleolide ATP play different roles in the nervous system. Adenosine acts on a family of G protein coupled receptors, collectively called adenosine receptors or Pr purinoceptors. Four members of this family have been cloned and pharmacologically characterized: A 1 , A 2A , A 2B and A 3 . Their distribution, pharmacology and biological roles are briefly discussed. In particular. The evidence that adenosine acting at A 1 receptors regulates the release of several neurotransmitters and that adenosine acting of A 2A receptors modulates dopaminergic transmission is summarized. ATP acts on receptors called P 2 purinoceptors, which appear to fall into at least two main families - G protein coupled receptors and intrinsic ion channels. Their subclassification is becoming clearer as receptors are cloned and new selective agonists and/or antagonists are becoming available. There is on interesting potential for development of drugs targeted at purines or their receptors

Nicotine dependence, midbrain dopamine systems and psychiatric disorders.

Abstract: Compelling evidence exists that tobacco-smoking represents a form of drug addiction to nicotine. Like several drugs of abuse, nicotine activates the mesolimbic dopamine system and this effect appears to be of critical importance for the reinforcing properties of the drug. Specifically, nicotine has been shown to increase burst activity in dopamine neurones of the ventral tegmental area, i.e. a mode of firing pattern in these cells which is physiologically associated with basic motivational processes underlying learning and cognitive behaviour. The stimulatory action of nicotine on mesolimbic dopamine neurones is exerted both at the somatodendritic and at the terminal levels. Yet, the release of dopamine in the nucleus accumbens induced by systemically administered nicotine is abolished by the nicotinic receptor antagonist, mecamylamine when administered locally in the ventral tegmental area, but not in the nucleus accumbens. Whereas continuous infusion of nicotine into the ventral tegmental area produces a long-lasting increase in accumbal dopamine release, analogously to the effect of systemically administered nicotine, continuous infusion of nicotine into the nucleus accumbens produces a very short-lasting dopamine release. Thus, nicotinic receptors in the ventral tegmental area appear to be more significant than those located in the nucleus accumbens for mediating the stimulatory effect of nicotine on dopamine release in the nucleus accumbens. The effect of nicotine on midbrain dopamine systems may help to explain the extremely high prevalence of tobacco-smoking in schizophrenics, who frequently display so-called hypofrontality, i.e. a reduced functional activity in the prefrontal cortex which provides a direct input to the ventral tegmental area dopamine cells. Specifically, the prefrontal cortex seems to control phasic activity, i.e. essentially burst firing, but not tonic activity in these neurones through glutamatergic pathways. Accordingly, impaired functional activity in the prefrontal cortex in the rat has been found to decrease burst firing in ventral tegmental dopamine cells, an effect which can be antagonized by nicotine pretreatment. Moreover, chronic, but not acute nicotine administration has been found to increase dopamine metabolism in the prefrontal cortex. Thus, the intense nicotine intake in psychotic individuals may, in effect, reflect an attempted self-medication. The finding that cigarette-smoking can help to normalize the impaired sensory gating in schizophrenic patients provides additional evidence for this notion. In summary, the physiological pattern of activation of dopamine neurones induced by nicotine may be particularly well suited for its ability to induce psychological dependence as well as to partly reverse a probably distorted dopamine signalling in psychotic individuals.

Uptake and Transport of Manganese in Primary and Secondary Olfactory Neurones in Pike

Abstract: γ-spectrometry and autoradiography were used to examine the axoplasmic flow of manganese in the olfactory nerves and to study the uptake of the metal in the brain after application of 54 Mn 2+ in the olfactory chambers of pikes. The results show that the 54 Mn 2+ is taken up in the olfactory receptor cells and is transported at a constant rate along the primary olfactory neurones into the brain. The maximal velocity for the transported 54 Mn 2+ was 2.90±0.21 mm/hr (mean±S.E.) at 10°, which was the temperature used in the experiments. The 54 Mn 2+ accumulated in the entire olfactory bulbs, although most marked in central and caudal parts. The metal was also seen to migrate into large areas of the telencephalon, apparently mainly via the secondary olfactory axons present in the medial olfactory tract. A transfer along fibres of the medial olfactory tract probably also explains the labelling which was seen in the diencephalon down to the hypothalamus. The results also showed that there is a pathway connecting the two olfactory bulbs of the pike and that this can carry the metal. Our data further showed a marked accumulation of 54 Mn 2+ in the meningeal epithelium and in the contents of the meningeal sacs surrounding the olfactory bulbs. It appears from our study that manganese has the ability to pass the synaptic junctions between the primary and the secondary olfactory neurones in the olfactory bulbs and to migrate along secondary olfactory pathways into the telencephalon and the diencephalon. Manganese is a neurotoxic metal which in man can induce an extrapyramidal motor system dysfunction associated with occupational inhalation of manganese-containing dusts or fumes. We propose on basis of our results that the neurotoxicity of inhaled manganese may be related to an uptake of the metal into the brain via the olfactory neurones. The manganese can thereby circumvent the blood-brain barrier and gain direct access to the central nervous system.

3,3′,4,4′‐Tetrachlorobiphenyl Effects on Antioxidant Enzymes and Glutathione Status in Different Tissues of Rainbow Trout

Abstract: Polychlorinated biphenyls are known to cause induction in cytochrome P450-dependent monooxygenase activities and alteration in the antioxidant defense of mammals. To determine whether similar detoxication processes are activated in rainbow trout (Oncorhynchus mykiss), we investigated P450-dependent enzyme activities, antioxidant enzymes and glutathione status (reduced and oxidized glutathione, GSH and GSSG) in this species injected intraperitoneally with 3,3',4,4'-tetrachlorobiphenyl at 5 mg/kg body weight 6 weeks post injection. Ethoxyresorufin O-deethylase activities increased 11- and 40-fold in liver and kidney. UDPglucuronosyltransferase activities were 2- and 5-fold higher in these organs, while glutathione S-transferase activity was enhanced greater than 2-fold in liver of tetrachlorobiphenyl injected trout in comparison with controls. Glutathione peroxidase activities were increased in liver and white muscle of dosed fish. Tetrachlorobiphenyl exposure resulted in a significant increase in glutathione reductase activities, with 7-fold enhancement in liver and significantly elevated activities in kidney, red and white muscles. Similarly, cytosolic superoxide dismutase and catalase activities were increased in white muscle of injected trout. Tetrachlorobiphenyl exposure significantly increased GSH concentrations in liver and kidney, while GSSG levels were increased in liver and blood plasma. These changes, however, did not modify the GSSG/GSH ratios in these tissues. Overall, these results imply a major tetrachlorobiphenyl effect on GSH status and antioxidant enzymes in trout tissues and identify white muscle along with liver and kidney as important tissues in the detoxication process in this animal.

Purinergic inhibition of neurotransmitter release in the central nervous system

Abstract: Neurotransmitter release and the role of adenosine in its regulation has been investigated for more than twenty years, and it is now widely accepted that adenosine tonically inhibits the release of excitatory neurotransmitters. This effect of adenosine is operated by an A1 adenosine receptor. Since activation of this receptor could inhibit Ca2+ conductance, increase K+ conductance, inhibit adenylate cyclase or phospholipase C, it is not clear if there is only one mechanism or several mechanisms operated by adenosine to inhibit neurotransmitter release, and in that case, what is the relative importance of each mechanism. The mechanism by which adenosine inhibits evoked synchronous transmitter release might be different from that used by the nucleoside to inhibit spontaneous asynchronous release. In some systems adenosine triphosphate per se acts like adenosine and inhibits neurotransmitter release. However, in most cases the inhibitory effect of this adenine nucleotide depends upon its hydrolysis into adenosine by a cascade of ectoenzymes, the last step being mediated by ecto-5'-nucleotidase.

Hepatocellular regeneration : key to thioacetamide autoprotection

Abstract: Low doses of thioacetamide stimulate cell division and tissue repair in the liver. The objective of this study was to develop an autoprotection model for thioacetamide and investigate if a low dose of thioacetamide (50 mg/kg orally) protects against lethality of a subsequently administered lethal dose (400 mg/kg orally) of the same compound. The extent of cell division was investigated to test if autoprotection results from augmented tissue repair and recovery from injury rather than decreased injury itself. After a single administration of the protective dose of thioacetamide, hepatocellular nuclear DNA synthesis as measured by 3H-thymidine incorporation into hepatocellular nuclear DNA peaked at 36 hr indicating maximum level of S-phase stimulation. Pretreatment with the antimitotic colchicine abolished autoprotection and this was associated with a significantly decreased 3H-thymidine incorporation. Preadministration of the protective dose of thioacetamide did not result in an altered infliction of injury from the subsequently administered lethal dose. Colchicine intervention in the autoprotected group resulted in injury that followed a pattern similar to the group that received the high dose alone, ultimately resulting in animal death. These findings suggest that cell division stimulated by the protective low dose of thioacetamide is the critical mechanism in thioacetamide autoprotection.

Metabolism‐Dependent Toxicity of Methimazole in the Olfactory Nasal Mucosa

Abstract: In mice given a single intraperitoneal injection of the antithyroid drug methimazole (0.44 mmol/kg; 50 mg/kg) detachment of the olfactory neuroepithelium and necrosis of the Bowman's glands in the lamina propria was observed 24 hr after administration. Three days after administration there was an atypical epithelium throughout the olfactory region and the Bowman's glands had disappeared. Pretreatment with the olfactory cytochrome P450 inhibitor metyrapone protected against the methimazole-induced changes at this site. In mice injected with the methimazole analogues 1-methylimidazole or 4-methylimidazole (0.44 mmol/kg; 36 mg/kg) or the antithyroid drug propylthiuracil (0.22 mmol/kg; 38 mg/kg) no morphological changes were observed in the olfactory mucosa. The results suggest that methimazole-induced toxicity in the olfactory mucosa is related to metabolism-dependent changes of the thiol group.

Different β‐Adrenergic Receptor Density in Different Rat Skeletal Muscle Fibre Types

Abstract: The effects of adrenaline on skeletal muscle differ between fibre types. The aim of the present study was to investigate the β-adrenoceptor density, affinity and subtype in rat skeletal muscles with different fibre type composition. β-Adrenoceptors were determined in cryostat sections to avoid methodological problems with variable recovery, using the non-selective β-adrenoceptor ligand [ 3 H]CGP-12111 and β 1 - and β 2 -selective cold ligands CGP 20112A and ICI 118,551. In the presence of protease inhibitors [ 3 H]CGP-12111 binding was stable, saturable, reversible, and displaceable. Scatchard analysis of binding saturation data was compatible with a single class of specific binding sites. Binding site density (B max ) was higher (P<0.02) IN ADULT SOLEUS (9.38±1.13 FMOL×MG PROTEIN -1 ) than in adult extensor digitorum longus (4.14±0.39 fmol×mg protein -1 ), whereas the dissociation constants (K d ), 0.31±0.05 and 0.31±0.04 nM for soleus and extensor digitorum longus, respectively, were not significantly different. For young rats (5-6 weeks), B max was 11.21±0.33 and 5.45±0.11 fmol×mg protein -1 (P<0.05), AND K d was 0.21±0.02 and 0.24±0.04 nM for soleus and epitrochlearis, respectively. These results correspond to a receptor density of 2 and 1 pmol×g w.wt. -1 in muscles containing mainly type I and type II fibres, respectively. Displacement studies with CGP 20112A and ICI 118,551 were compatible with mainly β 2 -adrenoceptors, but 1-10% β 1 -adrenoceptors were present in both types of muscle. In conclusion, the receptor density is twice as high in muscles containing mainly type I muscle fibres compared to muscles containing mainly type II fibres, and this may explain some of the different effects of adrenaline between the two muscle fibre types

Angiotensin Receptors in the Brain

Abstract: Angiotensin receptors have recently become a focus of scientific interest due to the recent development of specific receptor ligands which allow to distinguish between various angiotensin II receptor subtypes, notably the angiotensin II type 1 receptor (AT1) and angiotensin II type 2 receptor (AT2). Although both receptors belong to the seven transmembrane domain receptor family they feature less than 35% homology and differ in their signal transduction mechanisms and in the effects mediated. In the brain, both angiotensin receptor types and probably some further subtypes are present and have been localized in distinct regions. In the adult brain, the AT1 receptor dominates by far and is responsible for most of the known central actions of angiotensin peptides, for example blood pressure increase, release of vasopressin from the pituitary gland, natriuresis, drinking and induction of immediate early genes in distinct brain areas. Some of the AT1 receptor-mediated effects have been shown to be enhanced by blockade of AT2 receptors in the brain suggesting that the central AT2 receptor can exert an inhibitory control on AT1 receptor-mediated actions in the brain.

The Contribution of Lysosomal Trapping in the Uptake of Desipramine and Chloroquine by Different Tissues

Abstract: Cationic amphiphilic drugs strongly accumulate in tissues of different organs. Uptake is controlled by two major mechanisms, non-specific binding to membrane phospholipids, and ion-trapping within acidic cellular compartments. The aim of this study was to assess the individual contributions of these two mechanisms on the uptake in vitro of desipramine and chloroquine into tissue slices of control and desipramine-treated rats. Drug uptake into intact slices was compared with uptake into slices with destroyed or non-functional acidic compartments. The sequence of desipramine uptake by tissue slices of eight different organs was: lungs > brain > heart > diaphragm > kidneys > skeletal muscles > adipose tissue > liver. The low desipramine concentration in liver may be due to metabolism of the parent drug by cytochrome P-450. Uptake of chloroquine differed widely between slices of different organs with the sequence: lungs > kidneys = brain = liver > diaphragm = heart = skeletal muscles > adipose tissue. Destruction or inactivation of the acidic compartments by homogenization and freeze-thawing or by ammonium chloride, sodium fluoride, or monensin, reduced drug uptake to similar extents. The reduction was organ-specific and may represent the size of the lysosomal compartment in the respective tissue cells. Uptake of chloroquine was more affected than that of desipramine, suggesting that ion-trapping is the main factor for chloroquine accumulation, while binding to membrane phospholipids, is the main factor for desipramine uptake. Single or multiple-dose treatments of rats with desipramine hardly had any effect on consecutive desipramine uptake into lung and liver slices, while the accumulation of chloroquine was enhanced in these slices. In conclusion, the extent of uptake of cationic amphiphilic drugs into tissue slices was tissue-specific, and the contribution of the two uptake mechanisms was strongly drug-dependent.

Comparison of the binding activities of some drugs on alpha 2A, alpha 2B and alpha 2C-adrenoceptors and non-adrenergic imidazoline sites in the guinea pig.

Abstract: Simultaneous computer modelling of control and guanfacine-masked [ 3 H]-MK 912 saturation curves as well as guanfacine competition curves revealed that both α 2A - and α 2C -adrenoceptor subtypes were present in the guinea pig cerebral cortex. The K d value of [ 3 H]-MK 912 determined for the α 2A -subtype was 403 pM and for the α 2C -subtype 79.8 pM; the receptor sites showing capacities 172 and 19.5 fmol/mg protein, respectively. The K d s of guanfacine were 20 and 880 nM for the α 2A - and α 2C -adrenoceptor, respectively. In the guinea pig kidney [ 3 H]-MK 912 bound to a single saturable site with K d 8.34 nM and capacity 285 fmol/mg protein, the site showing pharmacological properties like an α 2B -adrenoceptor. Binding constants of 22 compounds for the three guinea pig α 2 -adrenoceptor subtypes were determined by com puter modelling competition curves using for the cerebral cortex a «3-curve assay», for the kidney an «1-curve assay», and using [ 3 H]-MK 912 as labelled ligand. Of the tested drugs guanfacine and BRL 44408 were found to be clearly α 2A -selective. Spiroxatrine, yohimbine, rauwolscine and WB 4101, as well as [ 3 H]-MK 912 itself, were found to be α 2C -selective. The most selective compounds for α 2B -adrenoceptors, when compared to α 2A -adrenoceptors, were ARC 239 and prazosin. In the guinea pig kidney [ 3 H]-p-aminoclonidine bound to α 2 -adrenoceptors as well as to non-adrenergic imidazoline sites. The α 2 -adrenoceptors could be completely blocked using 10 μM (-)-adrenaline without the non-adrenergic sites being affected. During these conditions the analysis of combined saturation and competition studies using labelled and unlabelled p-aminoclonidine with computer modelling revealed that the ligand labelled two different sites with was of 310 and 47,000 nM, respectively. Competition curves of 16 compounds for the non-adrenergic [ 3 H]-p-aminoclonidine sites were shallow and resolved into two-site fits. For the high affinity [ 3 H]-p-aminoclonidine site the highest affinities were shown by 1-medetomidine, UK-14,304, guanabenz and detomidine; the K d s of these drugs ranging 26-72 nM. All drugs tested showed low but varying affinities for the low affinity [ 3 H]-p-aminoclonidine site. These data indicated that the [ 3 H]-p-aminoclonidine binding sites of the guinea pig kidney are grossly different from the [ 3 H]-idazoxan binding I 2 -receptors previously demonstrated also to be present in the guinea pig kidney

High Throughput Assays of Cloned Adrenergic, Muscarinic, Neurokinin, and Neurotrophin Receptors in Living Mammalian Cells

Abstract: Many receptors stimulate proliferation of NIH 3T3 cells in a ligand dependent fashion. Based on this observation, we developed a high throughput assay of cloned receptor pharmacology. In this assay, receptors are transiently co-expressed with the marker enzyme beta-galactosidase. Receptors that induce cellular proliferation select and amplify the cells that also express the marker, thus the ability of ligands to alter receptor activity are reported as changes in enzyme activity. In the present study, we used this assay to evaluate the ability of agonist ligands to stimulate four cloned receptors. The agonists phenylephrine, carbachol, substance P and nerve growth factor selectively stimulated cells transfected with the alpha-1b adrenergic, m4 muscarinic, NK1 neurokinin and trkA neurotrophin receptors, respectively. These data demonstrate that a high throughput colorimetric assay performed in 96 well plates can be used to evaluate the pharmacology of ligands for cloned receptors belonging to a wide range of functional and pharmacological classes.

The Effect of Nicotine and Its Interaction with Carbon Tetrachloride in the Rat Liver

Abstract: In order to study the effects of nicotine on liver, groups of rats were given nicotine doses that simulated those seen in chronic smoking (54 and 108 μmol/l of nicotine) for 10 days. A subgroup was also given a single subcutaneous injection of 6 g/kg of carbon tetrachloride (CCl4) shortly before the animals of the group were killed. Histology demonstrated a significant hepatotoxic effect in the group receiving 108 μmol/l of nicotine when compared with the control group in the form of fatty change, focal or confluent necrosis and dark-cell change. The effects in pregnant rats were less severe. Carbon tetrachloride alone induced significant fatty change and focal necrosis in non-pregnant rats but not in pregnant rats. Nicotine also aggravated the CCl4 induced pathological changes in livers of both non-pregnant and pregnant animals. Thus nicotine alone, when given at a concentration of 108 μmol/l, exerted hepatotoxic effects; the alkaloid also aggravated the hepatotoxicity of CCl4. Pregnant rats were more resistant to the hepatotoxic effects produced by nicotine and CCl4.

Calcipotriol: A New Drug for Topical Psoriasis Treatment

Abstract: Vitamin D is best known for its role in the regulation of calcium and bone metabolism. The effects of the biologically active form of vitamin D, 1,25-dihydroxyvitamin D 3 (1,25 (OH) 2 D 3 ), are mediated by binding to a specific intracellular vitamin D receptor, which is present in most tissues including the skin where it regulates the growth of epidermal cells. Calcipotriol is a synthetic analogue of 1,25(OH) 2 D 3 . In vitro the activity of calcipotriol is comparable to that of 1,25(OH) 2 D 3 . In vivo, however, the risk of calcipotriol changing calcium metabolism is greatly reduced. Animal studies have established that calcipotriol is 100-200 times less calcaemic than 1,25 (OH) 2 -D 3 . This low calcaemic activity is mainly due to the rapid metabolism of calcipotriol. This pharmacological profile makes calcipotriol an ideal candidate for topical treatment of hyperproliferative skin disorders, such as psoriasis. This paper reviews the clinical experience with calcipotriol in psoriasis patients.

Cytochrome P4502E1 inhibition by propylene glycol prevents acetaminophen (paracetamol) hepatotoxicity in mice without cytochrome P4501A2 inhibition

Abstract: Acetaminophen hepatotoxicity is associated with its biotransformation to the reactive metabolite N-acetyl-p-benzoquinone imine that binds to protein. Two forms of cytochrome P450, CYP2E1 and CYP1A2, have been implicated as primarily responsible for the bioactivation. To determine the relative contributions of these P450's, overnight fasted male NMRI mice were pretreated with 10 ml of 50% v/w propylene glycol/kg or fluvoxamine (10 mg/kg) at -80 and -20 min. relative to acetaminophen dosing to inhibit CYP2E1 and CYP1A2, respectively. Mice were sacrificed at 0.5 or 4 hr after a hepatotoxic dose of acetaminophen (300 mg/kg). Propylene glycol or propylene glycol plus fluvoxamine, but not fluvoxamine alone protected against acetaminophen hepatotoxicity as indicated by abolished increase in serum alanine aminotransferase activity, less depletion of hepatic glutathione and lower liver:body weight ratios. Propylene glycol inhibited the activity of CYP2E1 as indicated by 84% reduction in the clearance of 3 mg/kg dose of chlorzoxazone, whereas fluvoxamine inhibited the activity of CYP1A2 as indicated by 40% reduction in the clearance of a 10 mg/kg dose of caffeine. For this animal model, the data are consistent with the notion that hepatoxicity is associated with bioactivation of acetaminophen by CYP2E1 but not by CYP1A2.

Serotonergic Mechanisms Involved in the Exploratory Behaviour of Mice in a Fully Automated Two-Compartment Black and White Test Box

Abstract: A fully automated version of the black and white two-compartment box for mice is presented. The anxiolytic-like effects of the benzodiazepines, diazepam and chlordiazepoxide, were confirmed, and the involvement of serotonergic mechanisms was studied in this animal model of anxiety. The partial 5-HT 1A receptor agonists, buspirone and ipsapirone showed anxiolytic-like effects in a limited dose interval. The full agonist hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) was inactive. The non-selective 5-HT 1 receptor agonist, eltoprazine, induced marked increases of exploratory behaviour in the white compartment over a broad range of doses. Also pindolol a mixed 5-HT 1A/1B and β-adrenergic receptor antagonist showed anxiolytic-like effects, whereas another compound with a similar profile (-)-, penbutolol and the β-adrenoceptor antagonist ICI 118,551, was inactive. The 5-HT 2A/2C receptor antagonist, ritanserin, showed anxiogenic-like, and the 5-HT 3 receptor antagonists, zacopride and ondansetron, showed anixiolytic-like effects. An overall increase of serotonergic activity by means of 5-HT uptake inhibition (citalopram), 5-HT release (fenfluramine) or administration of a 5-HT precursor (1-5-HTP) facilitated exploratory activity in the white compartment. Reduction of serotonergic activity by treatment with the 5-HT depletor p-chloro-phenylalanine methyl ester (PCPA) did not change the exploratory behaviour, but attenuated the response to fenfluramine significantly.

Transfer of Lidocaine and Bupivacaine Across the Isolated Perfused Human Placenta

Abstract: Drug permeability and pharmacokinetics through the placenta are important factors determining foetal drug exposure The purpose of the present study was to establish a perfused human placental cotyledon system to assess the placental transfer of lidocaine and bupivacaine, widely used local anaesthetics in obstetric anaesthesia Term placentas were obtained immediately after delivery with maternal consent and a two-hour recycling perfusion of a single placental cotyledon was performed Bupivacaine or lidocaine with antipyrine as a reference compound were added to the maternal reservoir and their disappearance from the maternal circulation and appearance to the foetal circulation were followed in five experiments for each drug Drug concentrations were measured by gas chromatography Bupivacaine disappeared more rapidly from the maternal circulation than lidocaine At 2 hr, bupivacaine foetal:maternal concentration ratio was 056 +/- 012 and 146% +/- 299 of the total circulating amount was found in the foetal circulation Lidocaine concentration increased more in the foetal circulation and the foetal:maternal concentration ratio at 2 hr was 090 +/- 009 (P < 001), and 221% +/- 221 (P < 001) was found in the foetal circulation The maternal to foetal transfer of bupivacaine and lidocaine were 672% +/- 0153 and 989% +/- 007 (P < 005) of that of freely diffusable antipyrine, respectively Both amide local anaesthetics crossed the dually perfused human placenta rapidly Bupivacaine disappeared faster than lidocaine from the maternal circulation but less was transferred to foetal circulation This difference is probably explained by the greater lipophilicity of bupivacaine and hence higher placental binding These results suggest less foetal drug exposure with bupivacaine than lidocaine

Effect of p‐Chlorophenylalanine and α‐Methyltyrosine on the Antinociceptive Effect of Antidepressant Drugs

Abstract: The role of para-chlorophenylalanine and alpha-methyl-DL-p-tyrosine in the antinociceptive effects of the intracerebroventricular administration of the antidepressant drugs clomipramine, zimelidine, imipramine and maprotiline was studied using the acetic acid writhing test in mice. The results demonstrated an antinociceptive effect for all these antidepressants. Pretreatment with para-chlorophenylalanine significantly reduced the antinociception induced by the ED50's of imipramine and maprotiline, and did not modify the effects of zimelidine and clomipramine, pretreatment with alpha-methyl-tyrosine did not modify the antinociception induced by these drugs except maprotiline. Pretreatment with para-chlorophenylalanine plus alpha-methyltyrosine significantly reduced the antinociceptive effect of all the antidepressants tested. The main finding of the present study is that the association of para-chlorophenylalanine plus alpha-methyltyrosine reduced the antinociceptive action of all the antidepressants. This means that critical levels of both 5-HT and NA are responsible for mediating the antinociceptive effects of antidepressants on the writhing test in mice.

Characterization of a P2Y Purinoceptor in the Brain

Abstract: Little has been known of the abundance in the brain of any of the G protein coupled P2 purinoceptors nor their pharmacology. Here we show that [35S]dATP alpha S is a suitable radioligand for investigating these receptors and hence that they are exceptionally abundant both in one-day-old chick (Bmax: 37 pmol agonist sites/mg protein) and adult rat brain membranes (Bmax: 39 pmol/mg protein). [35S]dATP alpha S (which is selective for P2Y over the P2X types of purinoceptor) binds with high affinity to these sites in the chick (Kd: 13.3 nM) and in the rat brain membranes (Kd: 9.1 nM). The rank order of potency of purinoceptor-active agonists and antagonists displacing [35S]dATP alpha S binding is: dATP alpha S > (3'-deoxyATP, 2-methylthioATP, ATP alpha S, ATP) > 2'-deoxyATP > 2-methylthioADP > ADP >> suramin, Reactive Blue-2 >> UTP, L-beta,gamma-methyleneATP, adenosine; this defines these binding sites as P2Y subtypes of the P2 purinoceptors. This pharmacological profile of purinergic ligands is in excellent agreement with the potency order established for the recombinant P2Y1 purinoceptor from chick brain, identifying the great majority of the brain P2 purinoceptors as identical or very similar to the native P2Y1 receptor.

Role of Ca2+ on endotoxin-sensitivity by galactosamine challenge : lipid peroxide formation and hepatotoxicity in zymosan-primed mice

Abstract: This study was investigated to clarify the role of intracellular Ca2+ following endotoxin treatment (1 mg/kg, intraperitoneally) to D-galactosamine-sensitized mice (400 mg/kg, intraperitoneally), and to observe lipid peroxide levels, an index of hepatotoxicity, in endotoxin/galactosamine (Ga1N)-challenged mice under activation of macrophages, especially Kupffer cells, by zymosan. The liver lipid peroxide level and serum glutamic pyruvic transminase activity in mice 18 hr after administration of endotoxin/Ga1N were markedly higher than those in mice treated only with endotoxin. In spite of an increase in lipid peroxide formation, there was little or no effect of Ga1N administration on xanthine oxidase and superoxide dismutase activities in mice given endotoxin. However, the injection of verapamil (10 mg/kg, subcutaneously) markedly decreased lipid peroxide levels in liver of endotoxin/Ga1N-injected mice. In the mice given a Ca(2+)-deficient diet, lipid peroxide level in liver after endotoxin/Ga1N injection was markedly decreased compared to that in mice fed a normal diet. Administration of dexamethasone (200 micrograms/kg, intraperitoneally) in mice 1 hr before treatment with endotoxin/Ga1N did not induce lipid peroxide formation. Administration of endotoxin to Ga1N-treated mice resulted in a higher level of liver cytosolic free Ca2+ ([Ca2+]i) than that in endotoxin-treated mice. On the other hand, Ca(2+)-ATPase activity in liver plasma membrane in the endotoxin/Ga1N-treated mice was markedly decreased as compared with endotoxin alone. On the contrary, the Ca(2+)-ATPase activity in liver mitochondria was higher in endotoxaemic mice treated with GA1N than in mice given endotoxin alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions Between Endothelial Mediators

Abstract: Prostacyclin, nitric oxide and tissue plasminogen activator constitute a prominent triad of endothelial mediators. Prostacyclin is responsible mainly for maintaining vascular thromboresistance against platelet clumps, inhibits proliferation of vascular smooth muscle and modulates cholesterol turnover, tissue plasminogen activator is a fibrinolytic agent and nitric oxide controls vascular tone and structure. Receptor agonists such as acetylcholine, kinins, endothelins or adenosine diphosphate evoke a coupled release of mediators from endothelial cells. Prostacyclin and nitric oxide synergize in their antiplatelet, fibrinolytic and cardioprotective, but not in their hypotensive actions. Prostacyclin, but not nitric oxide, prevents paradox thrombogenic effects of tissue plasminogen activator. Filogenetically, prostacyclin and tissue plasminogen activator are younger brothers of nitric oxide from which they take over and perfect regulatory properties in circulation. Further studies on interactions of endothelial mediators may lead to a better understanding of mechanisms of thrombosis, atherogenesis, diabetic angiopathies, endotoxic shock and arterial hypertension.

The effect of a benzalkonium chloride-containing nasal spray on human respiratory mucosa in vitro as a function of concentration and time of action.

Abstract: Human respiratory mucosa was exposed to oxymetazoline nasal spray in varying concentrations and for varying periods of time in vitro. The drug destroyed the tissue in a concentration- and time-dependent manner. In the experiments with various concentrations of the spray, some tissue fragments retained their viability throughout the experiment. This number increased parallel to a decrease in concentrations of the test substance. All the tissue fragments exposed to undiluted nose spray underwent severe destructive alterations during the exposure period. These alterations appeared first and were most extensive in those exposed for the longest periods of time. It has previously been demonstrated that the toxic effect of oxymetazoline nasal spray in vitro is probably due to the preservative benzalkonium chloride. The apparent lack of consistency between the toxic effects of benzalkonium chloride in vitro and in vivo is discussed, with special reference to protective systems absent in vitro but present in vivo.

Quantitative and Qualitative Distribution of Mercury in Organs from Arctic Sledgedogs: An Atomic Absorption Spectrophotometric and Histochemical Study of Tissue Samples from Natural Long‐Termed High Dietary Organic Mercury‐Exposed Dogs from Thule, Greenland

Abstract: Organs from 10 sledgedogs fed methyl mercury-containing organs and meat from predatory marine animals also eaten by humans in the Thule district of Greenland, were examined histochemically for cellular distribution of mercury, and the organ concentrations of mercury were quantified by atomic absorption spectrometry (total Hg). In selected organs the methyl mercuric level was determined by gaschromatography. The highest concentration of total mercury was found in mesenterial lymph nodes followed by liver and kidneys, which indicates that the lymphatic system might play an important role in the regulating transport of mercury to target organs. The concentrations were age-related, and the results suggest that demethylation takes place in all organs except skeletal muscles, but lowest in CNS. The distribution of mercury at cellular and subcellular levels was studied by the autometallographic technique. The atomic absorption spectrometric and autometallographic results were in good agreement. The brain mean concentration in the oldest group was 438 micrograms/kg, a level much lower than what has been reported to cause effects in the human central nervous system. However, if humans over a period of e.g. 50 years eat Arctic marine meat and accumulate mercury in the same way as dogs, the possibility that this may have health implications cannot be entirely excluded.

Depletion of Copper and Manganese in Brain after MPTP Treatment of Mice

Abstract: The mechanism of action of MPTP, a parkinsonism-inducing drug has been related to trace metals as a result of the observed potentiation of the neurotoxic action of the drug when diethyldithiocarbamate is concurrently administered. Diethyldithiocarbamate is a well-known chelator of trace metals, particularly copper. In the present study we analyzed the concentrations of copper and manganese in four brain regions of mice treated with neurotoxic doses of MPTP, in order to further substantiate the relationship between trace metals of MPTP-induced neurotoxicity. Male Swiss albino mice were administered with MPTP (30 mg/kg) for either three or five days. Seven days after the last MPTP administration, they were sacrified and the content of manganese and copper in the following regions was determined by graphite furnace atomic absorption spectrophotometry: cortex, cerebellum, midbrain and corpus striatum. Results indicate a significant depletion of manganese in corpus striatum (19.5% versus control) in the mice treated with MPTP for 5 days. Copper was also found to be decreased in corpus striatum (17.3% in mice treated for 3 days and 51.3% in mice treated for 5 days). Midbrain copper was depleted by 42.9% in the group of mice treated for 5 days with MPTP. Results indicate that MPTP induced a diminution of both copper and manganese in corpus striatum, suggesting that this alteration could be related to MPTP mechanism of action.

Changes in serotonin metabolism during treatment with the aldehyde dehydrogenase inhibitors disulfiram and cyanamide.

Abstract: The effect of the aldehyde dehydrogenase inhibitors disulfiram (Antabuse®) and cyanamide (calcium carbimide, Dipsan®) on the metabolism of serotonin measured as relative amounts of the metabolites 5-hydroxyindole-3-acetic acid and 5-hydroxytryptophol in urine were studied in alcoholic patients. Sixteen out of 23 patients receiving drug therapy showed elevated excretion of 5-hydroxytryptophol. However, there was a marked, 15-fold, variability in 5-hydroxytryptophol excretion rate between patients. A high degree of variability was also seen in another group of patients studied before and after introduction of drug therapy. When patients were followed during the dose interval, a time-dependent response after each single dose could be observed. The disulfiram response lasted over the course of several days whereas the response to cyanamide lasted for less than 12 hr. It is concluded that treatment with disulfiram and cyanamide affects serotonin metabolism leading to increased production of 5-hydroxytryptophol, but there is a marked inter-individual variability in degree of response.

Proliferation of hepatocytes and attenuation from carbon tetrachloride hepatotoxicity by gadolinium chloride in rats.

Abstract: Intravenous injection of gadolinium chloride (GdCl3) at a dose of 10 mg/kg caused an increase in proliferating cell nuclear antigen labeling index and the grade of pyronin positivity (RNA level) in rat liver. In CCl4-exposed rats, pretreatment with GdCl3 also showed a preventive effect of the liver injury both biochemically and histologically. Moreover, the proliferative action preceded the attenuative effect of the liver injury. Results suggest that GdCl3 induces hepatocyte proliferation, and this action of GdCl3 may modify the development of CCl4-induced liver injury.

Protective Effects of Antioxidants Against Uraemia‐Induced Lipid Peroxidation and Glutathione Depletion in Humans

Abstract: The effects of uraemias and antioxidant therapy for 40 days with vitamin A, vitamin C and vitamin E on blood and erythrocyte sulfhydryl (glutathione, GSH) content and on erythrocyte glutathione-S transferase (GST), glutathione reductase (GSR) and glutathione peroxidase activities were studied in six uraemic patients maintained on haemodialysis. In addition, the effect of antioxidant therapy on erythrocyte lipid peroxidation was determined, and erythrocyte haemoglobin content was measured. Uraemic patients in dialysis exhibited significant decreases in blood and erythrocyte GSH content as well as significant decreases in the activities of GST, GSR and GSH-peroxidase relative to control subjects. Furthermore, the uraemic patients had elevated erythrocyte malondialdehyde levels. Blood and erythrocyte GSH content from uraemic patients was significantly elevated after 20 days of antioxidant treatment and remained elevated thereafter throughout the remaining 20 days of the study (130% and 173%, respectively). Antioxidant therapy also produced significant increases in GSR and GSH-peroxidase activities after 20 days of treatment which remained relatively constant thereafter. No significant change in GST activity was observed. Erythrocyte malondialdehyde levels, as an index of oxidative tissue damage, exhibited a significant decrease (70%) in the patients after 40 days of antioxidant therapy. A gradual increase in erythrocyte haemoglobin content was observed following treatment of the uraemic subjects (45% at day 40). The results suggest that antioxidant therapy may protect against oxidative stress associated with uraemia.