Mazindol anorexia is mediated by activation of dopaminergic mechanisms.

1 Anorexia in rats following injections of mazindol (0.1-8 mg/kg i.p.) could be antagonized by pretreatment with a dopamine receptor blocker (primozide) but not by pretreatment with an alpha-adrenoceptor blocker (phenoxybenzamine), a beta-adrenoceptor blocker ((-)-propranolol), or a 5-hydroxytryptamine receptor blocker (methergoline). 2 In rats with a unilateral lesion in the substantia nigra made by stereotaxic injection of 6-hydroxydopamine, mazindol caused a dose-dependent turning towards the lesioned side, indicating an indirect mechanism of action. This effect could be antagonized by pretreatment with a dopamine receptor blocker. 3 In rats pretreated with reserpine and alpha-methyl-p-tyrosine, mazindol did not have any motor stimulant action. 4 In vitro studies with synaptosomes prepared from rat brain, indicated that mazindol blocks uptake and causes release of dopamine. 5 It is concluded that the anorectic action of mazindol is mediated by a dopaminergic mechanism.     

Cocaine-induced liver injury in mice is mediated by nitric oxide and reactive oxygen species

The modulating effects of nitric oxide (NO) and reactive oxygen species on cocaine-induced hepatotoxicity were examined by measuring plasma alanine aminotransferase activity and by carrying out histological studies. Liver injury was induced by a single injection of cocaine in adult male ICR mice. Pretreatment with aminoguanidine (an inhibitor of NO synthase), N-methyl-d-glucamine dithiocarbamate complex with iron ion (II) (Fe²⁺(MGD)₂, a trapping reagent of NO) or deferoxamine complex with iron ion (III) (Fe³⁺-deferoxamine, a scavenger of NO) produced a marked inhibition of the hepatotoxicity induced by cocaine. In addition, pretreatment with allopurinol (an inhibitor of xanthine oxidase) and 1,3-dimethylthiourea (a scavenger of hydroxyl radical) also produced a potent inhibition. These findings suggest that a hydroxyl radical produced by the reaction of NO and superoxide anion (O₂⁻) via peroxynitrite may be involved in the pathogenesis of cocaine hepatotoxicity.     

Augmentation of diltiazem on pentobarbital-induced sleep is mediated by the serotonergic system

AIM： To elucidate the the effects and mechanism （s） of diltiazem, a L - type Ca^2＋ antagonist, on the pentobarbital - induced sleep. METHODS： The polysomnogram consist of EEG and EMG was used for analyzing the sleep phenotypes. RESULTS： Diltiazem （2. 0 and 5.0mg/kg, p. o. ） increased both total pentobarbital - induced sleeping time and slow wave sleep （SWS）, and decreased the rapid eye movement （REM） sleep. These effects were potentiated by 5 - hydroxytryptophan （5 - HTP）, the immediate precursor of serotonin. Pretreatment of p - chlorophenylalanine （ PCPA, 400mg/kg, i. p. ）, a specific, potent and irreversible inhibitor of tryptophan 5 - monooxygenase,     

Pharmacological bronchodilation is partially mediated by reduced airway wall stiffness

Background and Purpose

In asthmatic patients, airflow limitation is at least partly reversed by administration of pharmacological bronchodilators, typically β₂-adrenoceptor agonists. In addition to receptor-mediated bronchodilation, the dynamic mechanical environment of the lung itself can reverse bronchoconstriction. We have now explored the possibility that bronchodilators exert a synergistic effect with oscillatory loads by virtue of reducing airway wall stiffness, and therefore, enhancing the bronchodilatory response to breathing manoeuvres.

Experimental Approach

Whole porcine bronchial segments in vitro were contracted to carbachol and relaxed to the non-specific β-adrenoceptor agonist, isoprenaline, under static conditions or during simulated breathing manoeuvres.

Key Results

The bronchodilatory response to isoprenaline was greater during breathing manoeuvres compared with the response under static conditions. As the bronchodilatory response to breathing manoeuvres is dependent upon airway smooth muscle (ASM) strain, and therefore, airway wall stiffness, our findings are likely to be explained by the effect of isoprenaline on reducing airway wall stiffness, which increased ASM strain, producing greater bronchodilation.

Conclusions and Implications

A contribution of reduced airway stiffness and increased ASM strain to the bronchodilator action of isoprenaline is shown, suggesting that oscillatory loads act synergistically with pharmacologically mediated bronchodilation. The implications for the treatment of asthma are that reducing airway wall stiffness represents a potential target for novel pharmacological agents.     

Antagonism of U-50,488H-induced antinociception by ginseng total saponins is dependent on serotonergic mechanisms.

Morphine-induced antinociception was prevented by pretreatment with ginseng total saponins in the tail-pinch and tail-flick tests carried out in mice. The antinociceptive effect of U-50,488H, a selective kappa-opioid receptor agonist, was prevented by naloxone, a nonselective opioid receptor antagonist, in the tail-pinch but not in the tail-flick test. However, U-50,488H-induced antinociception was prevented by ginseng total saponins in the tail-flick but not in the tail-pinch test. These results indicate that nonopioid mechanisms are involved in the antagonism of U-50,488H-induced antinociception by ginseng total saponins. In addition, the antagonism of U-50,488H-induced antinociception in mice pretreated with ginseng total saponins was abolished by pretreatment with a serotonin precursor, 5-hydroxytryptophan, but not by a noradrenaline precursor, L-dihydroxyphenylalanine, in the tail-flick test. Therefore, it appears that the antagonism of U-50,488H-induced antinociception by ginseng total saponins is dependent on serotonergic mechanisms.     

CCK-8-stimulated insulin secretion in vivo is mediated by CCKA receptors.

The effects of the cholecystokinin A (CCKA) receptor antagonist, L-364,718, and the CCKB receptor antagonist, L-365,260, on CCK-8-stimulated insulin secretion were studied in vivo in the mouse. It was found that CCK-8-stimulated insulin secretion was suppressed by L-364,718 at a low dose level (0.078 mumol/kg). In contrast, L-365,260 caused a partial inhibition of CCK-8-stimulated insulin release only at the high dose level (24 mumol/kg). It is concluded that the CCK-8-stimulated insulin release in vivo is mediated by CCK receptors of the CCKA subtype.     

PCB 118-induced endothelial cell apoptosis is partially mediated by excessive ROS production

Endothelial cell apoptosis, which may alter the integrity of the endothelium and lead to plaque instability, plays a critical role in the development and pathogenesis of atherosclerosis. Exposure of polychlorinated biphenyls (PCBs) is associated with increased risk of atherosclerosis and cardiovascular disease. In our present study, we explored whether exposure to PCB 118 influences endothelial cell apoptosis in vitro and the underlying mechanisms involved. As expected, exposure to PCB 118 increased the intracellular reactive oxygen species (ROS) levels in HUVECs. Increases in apoptosis and Bax/Bcl-2 ratios were observed in PCB 118-treated HUVECs. N-acetyl-l-cysteine (NAC), a ROS scavenger, partially reduced PCB 118-induced apoptosis and Bax/Bcl-2 ratios in HUVECs. Taken together, PCB 118-induced endothelial cell apoptosis was partially initiated by excessive ROS production.     

Beta-adrenoceptor agonist stimulation of acid secretion by rat stomach in vitro is mediated by 'atypical' beta-adrenoceptors.

1. A previous study showed beta-adrenoceptor agonists stimulated acid secretion by rat stomach in vitro. The receptors could not be classed as either the beta 1- or beta 2-subtype. This study examines the effect of 2 'atypical' beta-agonists on acid secretion. 2. Basal and isoprenaline-stimulated acid secretion were compared in tissues bathed either in HEPES/O2- or HCO3-/CO2-buffer. Basal secretion was underestimated in HCO3- by an amount equal to the rate of base section. Tissues responded well in HEPES buffer and there was no base secretion following acid inhibition with SCH 28080. HEPES was used for the study. 3. SR 58611A stimulated acid in a concentration-related way (0.1-5 microM). Maximum response at 1 microM was equal to the response to a maximal concentration of isoprenaline. BRL 37344 (1 microM) also stimulated to the same extent. 4. Responses to isoprenaline (5 microM) and SR 58611A (1 microM) were reduced by propranolol (10 microM) but not by alprenolol (10 microM) or by practolol (12.5 microM) plus ICI 118551 (1 microM). 5. Exposure to SR 58611A (1 microM) led to desensitization to isoprenaline but not to bethanechol (1 microM) or histamine (50 microM). 6. We conclude that a HEPES/O2-buffer is advantageous when measuring gastric acid secretion in vitro and the stimulatory effect of beta-adrenoceptor agonists is mediated by 'atypical' receptors.     

Effect of amlodipine on renin secretion and renin gene expression in rats.

1. This study was done to characterize the influence of calcium channel blockade on renin secretion and renin gene expression in normal rats and rats with renovascular hypertension. To this end we studied the effects of the 1,4-dihydropyridine derivative, amlodipine, on plasma renin activity and renal renin m-RNA levels in normal rats and rats with unilateral renal hypoperfusion induced by applying 0.2 mm left renal artery clips over four days. 2. In normotensive rats, amlodipine significantly decreased basal blood pressure by about 20 mmHg when applied in a concentration of 5, 15 and 45 mg kg-1. Plasma renin activity and also renin mRNA levels were not changed after application of 5 mg kg-1 of amlodipine. However, at a concentration of 15 or 45 mg kg-1, amlodipine, significantly increased not only plasma renin activity by about 250% and 300%, but also renin mRNA levels by about 100% and 500%. The action of amlodipine on all these parameters was maximal after 24 h. Treatment with amlodipine in a concentration of 15 mg kg-1 also increased renin immunoreactive areas in the kidney cortex by retrograde recruitment of renin expressing cells in the afferent arterioles. 3. In 2kidney-1 clip rats, systolic blood pressure rose continuously whilst plasma renin activity and renin m-RNA in the clipped kidney increased transiently and renin m-RNA in the contralateral kidney was constantly suppressed. Amlodipine at a concentration of 15 mg kg-1 markedly attenuated the increase of blood pressure in 2kidney-1 clip rats, produced an almost additive effect on plasma renin activity and showed a tendency to increase renin m-RNA levels in the clipped kidneys. Renin m-RNA levels in the contralateral kidney were also significantly suppressed in the animals receiving additional treatment with amlodipine. 4. These findings suggest that inhibition of calcium channels by amlodipine stimulates renin secretion and renin gene expression in vivo. These stimulatory effects are almost additive to the changes of renin secretion occurring after an unilateral fall of renal perfusion pressure.     

Morris water maze performance deficit produced by intermittent swim stress is partially mediated by norepinephrine

Intermittent swim stress (ISS) exposes a rat to cold water and the effects of the procedure produce detrimental results on activity measures 24 h later. The ISS model can be used with the Morris water maze (MWM) to investigate the impact of stress on a spatial learning and memory task, known to involve the hippocampus. We investigated if the ISS model produced performance deficits in the MWM (experiments 1 and 2). We also investigated the role of norepinephrine by using an alpha-2 adrenergic agonist (i.e., clonidine) to exacerbate ISS-induced deficits (experiment 3), and using antidepressants (i.e., desipramine and reboxetine) that enhance the synaptic availability of norepinephrine to reduce ISS-induced deficits (experiments 4 and 5). Results indicated a main effect for stress in all experiments, with the exception of experiment 2, as ISS did induce performance deficits in the MWM. Clonidine enhanced ISS-induced deficits only in the learning trials, while desipramine and reboxetine reduced ISS-induced deficits in the learning trials. Additionally, only reboxetine reduced memory deficits in the MWM. These findings provide evidence that norepinephrine may act as a partial mediator of ISS-induced deficits in MWM performance.     

Long-term effects of fenfluramine on central serotonergic mechanisms.

Consistent with results of previous studies, the present data indicate long-term changes in serotonergic neurons following a single injection of fenfluramine in rats. The brain levels of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan hydroxylase (TPH) activity and the synaptosomal uptake of ³H-5-HT were markedly reduced 2 weeks after 40 mg/kg of fenfluramine, and, with the exception of tryptophan hydroxylase activity, remained significantly decreased for at least 2 months. Although substantial recovery was evident between 2 weeks and 2 months, regional studies revealed marked reductions in some areas at 2 months. The largest reductions in 5-HT, 5-HIAA and 5-HT uptake were found in the hippocampus and cortex. The pattern of reduction of TPH was different, with the largest reductions in midbrain and limbic forebrain. The administration of 10 mg/kg of fluoxetine, a specific inhibitor of 5-HT uptake, prior to fenfluramine, prevented the long-term decreases in 5-HT, 5-HIAA and 5-HT uptake capacity, but not the decrease in TPH. These data suggest that the reduction in enzyme activity is mediated by a mechanism different from that responsible for the decreases in the other parameters. Thus, it is likely that the long-term effects of fenfluramine on brain 5-HT neurons can not be explained by a single mechanism such as an irreversible cytotoxic action.     

Central serotonergic mechanisms and development of morphine dependence.

The effects of different manipulations of brain serotonin (5-HT) content on the development of morphine dependence were investigated in rats, which were implanted with morphine pellets for 40 days. Serotonin content was decreased by (a) short or long term inhibition of tryptophan hydroxylase with para-chlorophenylalanine (PCPA), (b) by short or long term degeneration of 5-HT containing nerve terminals with 5,6-dihydroxytryptamine or (c) by degeneration of 5-HT containing nerve terminals by lesioning of midbrain raphe nuclei. With all methods used, the frequency of withdrawal jumping was significantly reduced, while other withdrawal signs remained more or less unchanged. Additional administration of 5-HTP to chronically PCPA treated rats did not reverse the PCPA effect. Since chronic reduction of 5-HT level during the whole time of morphine exposure changed withdrawal symptomatology in nearly the same way as did a decrease in 5-HT level during the time of withdrawal only, it is suggested that serotonergic mechanisms are not linked to the basic processes underlying dependence development but that they are only involved in the nervous pathways mediating the expression of some withdrawal signs.     

Capsazepine partially inhibits neurally mediated gastric mucus secretion following activation of protease-activated receptor 2

1. Protease-activated receptor 2 (PAR2), present in capsaicin-sensitive sensory neurons, induces gastric mucus secretion and mucosal cytoprotection. 2. We studied the possible cross-talk between PAR2 and vanilloid receptor 1 (VR1). The VR1 antagonist capsazepine partially inhibited the PAR2-mediated increase in gastric mucus secretion. 3. Thus, activation of VR1 is responsible, at least in part, for the neurally mediated mucosal cytoprotection following activation of PAR2.     

The stimulation of renin secretion by diazoxide in the isolated rat kidney.

The intrarenal effect of diazoxide on renin secretion was examined in the isolated perfused rat kidney. Mean renin secretion measured at 2 min intervals during the continuous infusion of diazoxide for 6 min was consistently higher than the corresponding control values, although this was significantly different at the end of the infusion only. Since renal perfusion pressure during diazoxide infusion and control studies decreased to a similar extent, it is suggested that diazoxide stimulates renin secretion by a direct effect on the juxtaglomerular cell.     

Flupirtine antinociception in the dog is primarily mediated by nonopioid supraspinal mechanisms

Flupirtine is a novel analgesic recently introduced with therapy. The present study assessed the role of opioid mechanisms in flupirtine-induced antinociception, localized its site of action along the neuraxis and evaluated its relative potency. Analgesic and general behavioral effects of flupirtine (0.3-10 mg/kg i.v.) were compared to those of the opioid analgesic pentazocine (0.3-5 mg/kg i.v.) in chronic spinal dogs. Flupirtine was slightly less effective than pentazocine in depressing the supraspinally mediated skin twitch nociceptive reflex. But in contrast to pentazocine, flupirtine only weakly depressed the flexor reflex, a spinally mediated nociceptive reflex. Statistically reliable potency estimates for antinociception were not obtained. Both drugs constricted pupils and lowered body temperature. In drug interaction studies, a relatively high dose (1 mg/kg i.v.) of the opioid antagonist naltrexone antagonized the effects of pentazocine but not those of flupirtine. It is concluded that flupirtine-induced antinociception is not opiate-receptor mediated, that its antinociceptive actions occur primarily at supraspinal sites and that its potency is less than that of pentazocine in the dog.