腺苷受体A1亚型对视网膜色素上皮细胞 免疫调节功能的影响

目的 研究视网膜色素上皮细胞（RPE）主要是通过何种亚型的腺苷受体（ARs）来结合腺苷,及其对 RPE 功能的影响。方法 体外培养人 ARPE-19 细胞系,定量 PCR 检测 4 种腺苷受体（ARA1、ARA2A、ARA2B、ARA3）基 因的表达;提取细胞膜蛋白,Western blot 检测 4 种腺苷受体在 RPE 细胞膜上的存在。体外培养 ARPE-19 细胞至 80% 融合后随机分为 A~E 组。其中,A 组为无干预对照组,B～E 组分别给予 ARA1 拮抗剂 DPCPX（50 nmol/L）、 ARA2A 拮抗剂 SCH58261（100 nmol/L）、ARA2B 拮抗剂 MRS1754（100 nmol/L）及 ARA3 拮抗剂 MRS1220（5 μmol/L） 干预。利用 H3-腺苷进行放射性配体结合实验,计算各组细胞对腺苷的最大结合容量（Bmax）。以肿瘤坏死因子 α （TNF-α）10 μg/L 及 γ 干扰素（IFN-γ）1 000 U/mL 联合干预体外培养的 ARPE-19 细胞,给予或不予 ARA1 激动剂 （CCPA）,酶联免疫吸附试验（ELISA）测定培养上清中白细胞介素（IL）-6、IL-10、转化生长因子 β（TGF-β）、单核细胞 趋化因子（MCP）-1、趋化因子 C-X-C 配体 10（CXCL10,IP-10）的含量。结果 在 ARPE-19 细胞中即可检测到 4 种 腺苷受体基因的表达,也可探测到其分子在细胞膜上的存在。A~E 组 ARPE-19 细胞结合腺苷的 Bmax （单位：fmol）分 别为 2.04±0.31、0.44±0.06、1.82±0.28、2.01±0.42 及 2.06±0.44,其中 B 组较其他各组 Bmax均降低（P＜0.01）。以 TNF- α 及 IFN-γ 激活 ARPE-19 细胞,与对照 RPE 组比较,CCPA 干预 RPE 组 IL-6、MCP-1 及 IP-10 的含量降低、IL-10 的含量增加（P＜0.01）。2 组 TGF-β 的含量差异无统计学意义。结论 ARA1 对 ARPE-19 细胞结合腺苷的能力具 有重要的调控作用,ARA1 受体介导的信号可抑制 ARPE-19 细胞分泌促炎因子及驱化因子,具有潜在的免疫抑制 作用。     

Specific antagonism of adenosine-induced bronchoconstriction in asthma by oral theophylline.

The airway response to increasing concentrations of inhaled-adenosine and histamine after oral theophylline or matched placebo was studied in nine asthmatic subjects. Changes in airway calibre were followed as sGaw and FEV1 and concentration-response curves constructed. Inhaled adenosine caused concentration-related bronchoconstriction and was four-five times less potent than inhaled histamine. Theophylline, which achieved a mean plasma level of 15.9 and 16.6 micrograms/ml on the histamine and adenosine study days respectively, caused significant increases in FEV1 (17%) and sGaw (41-53%) whereas placebo had no effect. Theophylline also protected the airways against histamine-and adenosine-induced bronchoconstriction. However theophylline had a greater protective effect against adenosine (concentration-ratio 17.4 for FEV1 and 12.8 for sGaw) than against histamine (concentration ratio 5.6 for FEV1 and 5.4 for sGaw (P less than 0.05]. At therapeutic concentrations theophylline is a specific antagonist of the airway effects of adenosine in addition to being a bronchodilator and a functional antagonist.     

Increase in plasma free fatty acids and natriuresis by xanthines may reflect adenosine antagonism

Summary The hypothesis has been examined that adenosine is involved in the diuretic and free fatty acid (FFA) — releasing action of xanthines. The effects of theophylline (T), a potent adenosine antagonist, were compared with those of enprofylline (3-propyl xanthine, E), which exerts negligible antagonism of adenosine. Eight healthy male volunteers were given E 1.5 mg/kg, T 5.0mg/kg or placebo 0.9% saline (P) intravenously in a double-blind, randomized, cross-over investigation. Blood samples were analyzed for E, T, catecholamines (CA: adrenaline, noradrenaline and dopamine), FFA, renin, glucose, glucagon and insulin, and urine was collected at 2-h intervals. T (plasma concentration 53±8 µmol/l) but not E (11±2 µmol/l) caused an increase in FFA from 0.42 to 0.86 mmol/l after 90 min. Without affecting the urinary excretion of potassium, T doubled natriuresis and the urine volume as compared to E and P. Neither T nor E had any effect on plasma CA, or on any other of the metabolic parameters studied. E, but not T, produced a small but statistically significant decrease in diastolic blood pressure (5 mmHg) and an increase in heart rate (3 beats/min). It is suggested that the difference between E and T in terms of stimulation of FFA-release and natriuresis may be related to their different ability to antagonize adenosine.     

Effects of caffeine with repeated dosing

Summary We have recently demonstrated dose-dependency of caffeine metabolism under multiple dosing conditions. Whether there are persistent pharmacodynamic actions of caffeine under such circumstances is the focus of this report. Nine healthy subjects were given, in randomized 5 day blocks, placebo, 4.2 (low) and 12 (high) mg · kg^–1 · day^–1 of caffeine in 6 divided doses.After 5 days, complete tolerance developed to the effects of caffeine on blood pressure, heart rate and plasma glucose concentrations. The 24-h area under the curve (AUC) for plasma norepinephrine and the AUC for the total sum of free fatty acids (FFA) both demonstrated a trend to increase with the high dose caffeine treatment. When the AUC for norepinephrine was split into 12 h time periods, a significant difference between the placebo and the high dose treatment block was seen.We conclude that regular consumption of 12 mg · kg^–1 of caffeine per day (equivalent to approximately 6 to 11 cups of coffee per day) may produce pharmacodynamic effects not completely compensated for by the development of tolerance. Mechanisms of tolerance may be overwhelmed by the nonlinear accumulation of caffeine and other methylxanthines in the body when caffeine metabolism becomes saturable.     

Effects of (-)-(R)-1-(p-hydroxyphenyl)-2-[3,4-dimethoxyphenethyl)amino]ethanol (TA-064), a new cardiotonic agent, on circulating parameters of carbohydrate and lipid metabolism in the rat

Effects of the new cardiotonic and selective beta 1-adrenergic agonist TA-064, (-)-(R)-1-(p-hydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino] ethanol, on circulating concentrations of glucose, lactate, free fatty acids (FFA), glycerol, cyclic AMP and the pancreatic hormones insulin (IRI) and glucagon (IRG) were examined in rats. TA-064, administered orally or intraperitoneally at the dose of 10 mg/kg (ca. 50 times the therapeutic dose) or higher, caused a slight transient rise followed by a persistent lowering of blood glucose concentrations, but it did not affect blood lactate levels at all. The same treatment with TA-064 elevated the concentrations of blood FFA, glycerol and plasma IRI and IRG. These changes induced by TA-064 were inhibited by pretreatment with propranolol (a non-selective beta-adrenergic antagonist) and practolol (a selective beta 1-adrenergic antagonist). The non-selective beta-adrenergic agonist isoproterenol and the selective beta 2-adrenergic agonist terbutaline elevated both blood glucose and lactate when administered intraperitoneally. They also brought about sustained rises in blood glycerol and plasma IRI, but only transiently increased the plasma IRG level. The cardiotonic agent prenalterol, claimed to be a selective beta 1-agonist, elevated blood glucose, lactate, and glycerol only slightly, and plasma IRI significantly, but it had no effect on plasma IRG. The cardiotonic agents dobutamine and amrinone also elevated blood glucose. Thus, TA-064 is unique among the beta-adrenergic and other cardiotonic agents in that it produces sustained hypoglycemia while it has no lactacidemic effect. Since this hypoglycemic action of TA-064 was always preceded by a rise in plasma IRI and abolished in streptozotocin-diabetic rats, we conclude that increased secretion of pancreatic insulin and the lack of hyperglycemic action are responsible for the hypoglycemia by high doses of TA-064.     

Adenosine receptor agonists inhibit inositol phosphate accumulation in rat striatal slices

The accumulation of inositol-1-phosphate in rat striatal slices was inhibited by the adenosine analogues 5'-N-ethylcarboxamide-adenosine and N6-phenylisopropyladenosine. Maximal inhibition (approximately 20%) was achieved by micromolar concentrations of either compound. Both basal and stimulated values could be inhibited, and the inhibition was reversible by the adenosine receptor antagonist 8-phenyltheophylline (10 microM). The results suggest that adenosine may exert a tonic inhibitory influence on inositol phospholipid-derived second messenger production in the striatum in vivo.     

Noribogaine generalization to the ibogaine stimulus: correlation with noribogaine concentration in rat brain.

The discriminative stimulus effects of ibogaine and noribogaine in rats have been examined in relation to their concentrations in blood plasma and brain regions and to receptor systems through which they have been proposed to act. Rats were trained to discriminate ibogaine (10 mg/kg i.p.), the NMDA antagonist dizocilpine (0.08 mg/kg i.p.) or the kappa-opioid agonist U50,488 (5 mg/kg i.p.) from vehicle in a standard two-lever operant conditioning procedure with a tandem VI-FR schedule of food reinforcement. Only rats trained on ibogaine generalized to noribogaine, which was approximately twice as potent as the parent compound. Noribogaine was detected in plasma and brain after administration of ibogaine and noribogaine. At the ED50 doses for the discriminative effect, the estimated concentrations of noribogaine in plasma, cerebral cortex, and striatum were similar regardless of whether ibogaine or noribogaine was administered. The findings suggest that the metabolite noribogaine may be devoid of NMDA antagonist and kappa-opioid agonist discriminative effects and that it may play a major role in mediating the discriminative stimulus effect of ibogaine.     

Does permanent carotid artery occlusion produce a 'preconditioning-like' effect towards more severe hypotension in energy metabolites? Role of cerebral adenosine

1. The aim of the present study was to investigate the potential energy preserving effect of permanent bilateral common carotid artery occlusion (BCCAO) towards additional systemic hypotension of severe duration (30 min). In addition, the role of adenosine A1 receptors in cerebral ischaemic preconditioning was investigated in male Wistar rats. Thus, oligaemic rats were assigned randomly to continuous treatment with the adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) or the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT), receiving daily intraperitoneal infusions of 0.1 mg/kg bodyweight CCPA or CPT or placebo (200 microL aqueous 2-hydropropyl-beta-cyclodextrin) at a delivery rate of 0.5 microL/h over 14 days. 2. Haemodynamic parameters and arterial blood gases were monitored. Rat cortical energy metabolites ATP, ADP, AMP, phosphocreatine and adenosine were measured using HPLC techniques. Adenosine A1 receptor expression was determined by immunhistochemistry and quantified by western blotting. 3. Two weeks of permanent BCCAO induced an 'energy saving' effect in rat cortical ATP concentrations. Under subchronic conditions, significant increases were detected in ADP and AMP concentrations after CCPA compared with placebo. Because similar changes were also seen after CPT, this adenosine A1 receptor-mediated effect does not seems to be specific. Furthermore, no differences in adenosine A1 receptor expression could be detected. 4. Adenosine was not specifically involved in the 'preconditioning-like' effect via the modulation of the adenosine A1 receptor in the present oligaemia model. Obviously, adenosine A1 receptor-specific effects after delayed cerebral ischaemic preconditioning do not seem to play an essential role if BCCAO is followed by a prolonged additional severe ischaemic event.     

The plasma protein extravasation induced by adenosine and its analogues in the rat dorsal skin: evidence for the involvement of capsaicin sensitive primary afferent neurones and mast cells

1. The contribution of sensory neurons and mast cells to the oedema evoked by adenosine A1 (N(6)-cyclopentyladenosine, CPA, 3 - 30 nmol site(-1)), A2 (5'N-ethylcarboxamidoadenosine, NECA, 1 - 10 nmol site(-1)) and A3 receptor agonists (N6-[3-iodobenzyl]-N-methyl-5'-carboxiamidoadenosine, IB-MECA, 0.01 - 3 nmol site(-1)) was investigated in the rat skin microvasculature, by the extravascular accumulation of intravenously-injected (i.v.) 125I-albumin. 2. Intradermal (i.d.) injection of adenosine and analogues induced increased microvascular permeability in a dose-dependent manner (IB-MECA > NECA > CPA > adenosine). The non-selective adenosine receptor antagonist theophylline (5 - 50 nmol site(-1)) markedly inhibited adenosine, CPA or NECA but not IB-MECA-induced plasma extravasation. The A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 0.3 - 3 micromol kg(-1), i.v.) significantly reduced CPA-induced plasma extravasation whereas responses to adenosine, NECA or IB-MECA were unchanged. The A2 receptor antagonist 3,7-dymethyl-1-proprargylxanthine (DMPX, 0.5 - 50 nmol site(-1)) significantly reduced NECA-induced plasma extravasation without affecting responses to adenosine, CPA and IB-MECA. 3. The tachykinin NK1 receptor antagonist (S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isopropoxyphenylacetyl) piperidin-3-yl] ethyl]-4-phenyl-1 azaniabicyclo [2.2.2]octane chloride (SR140333), but not the NK2 receptor antagonist (S)-N-methyl-N[4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl)butyl]-benzamide (SR48968), significantly inhibited the plasma extravasation evoked by higher doses of adenosine (100 nmol site(-1)), CPA (100 nmol site(-1)), NECA (1 nmol site(-1)) and IB-MECA (0.1 - 1 nmol site(-1)). In rats treated with capsaicin to destroy sensory neurons, the response to higher doses of adenosine, CPA and NECA, but not IB-MECA, was significantly inhibited. 4. The effects of adenosine and analogues were largely inhibited by histamine and 5-hydroxytryptamine (5-HT) antagonists and by compound 48/80 pretreatment. 5. In conclusion, our results provide evidence that adenosine A1 and A2, but not A3, receptor agonists may function as cutaneous neurogenic pro-inflammatory mediators; acting via microvascular permeability-increasing mechanisms that can, depending on dose of agonist and purine receptor under study, involve the tachykinin NK1 receptor and mast cell amines.     

A pharmacokinetic-pharmacodynamic model of tolerance to morphine analgesia during infusion in rats

A pharmacokinetic-pharmacodynamic (PK-PD) model was constructed to describe the kinetics of tolerance development to morphine-induced antinociception. Tail-flick latencies in response to hot water (50°C) were assessed in male Sprague-Dawley rats exposed to a 12-hr iv infusion of either morphine (1.4 to 3.0 mg/kg per hr) or saline. Morphine-induced antinociception, expressed as the percentage of maximum possible response (%MPR), peaked after 120 min of infusion and decreased thereafter despite sustained systemic morphine concentrations. Both the rate and extent of tolerance development increased with increasing concentrations; an overall residual effect of approximately 24% MPR was observed at the end of the infusion regardless of the steady-state morphine concentration. The kinetics of tolerance offset were examined in a separate experiment by assessing tail-flick latency 15 min after morphine iv bolus (2 mg/kg) in tolerant and control rats. Recovery of response neared completion 18.5 days after a 12-hr exposure to morphine (2.0 mg/kg per hr). A PK-PD model was constructed to account for the delay in onset of antinociceptive effect and tolerance development relative to the blood concentration-time profile. According to this model, both the extent and the rate of tolerance development were modulated by the kinetics of the drug in the central compartment. Accumulation of a hypothetical “inhibitor” acting either as a reverse agonist, a competitive or noncompetitive antagonist, or a partial agonist could potentially account for the loss of pharmacologic effect in the presence of an agonist. The rate of tolerance development predicted from the PK-PD model varied widely (28-fold) depending on the type of pharmacologic interaction selected to account for the loss of effect. Using the rate of tolerance offset to discriminate between the different models (t_1/2 offset 5.4 days), onset and offset of tolerance was described accurately by postulating that the inhibitor behaves as a partial agonist with low intrinsic activity (5.5% MPR) and high binding affinity for the receptor (IC₅₀ 15.0 ng/ml). Presented in part at the Seventh Annual Meeting of the American Association of Pharmaceutical Scientists, San Antonio, Texas, November 15–19, 1992.     

Participation of adenosine system in the ketamine-induced motor activity in mice

The influence of adenosine receptor ligands on ketamine-induced locomotor activity was studied in mice. Ketamine-induced hyperactivity (10 mg/kg) was significantly and dose-dependently attenuated by CGS 21680 (selective A(2A) receptor agonist), and NECA (A1/A2 adenosine receptor agonist), but not by CPA (cyclopentyladenosine, selective A1 adenosine receptor agonist). Motor activity produced by subthreshold dose (2.5 mg/kg) of ketamine was significantly increased by DMPX (selective A1 receptor antagonist) and caffeine (A1/A2 adenosine receptor antagonist), but not by DPCPX (selective A1 adenosine receptor antagonist). These results suggest that adenosinergic system is involved in ketamine-induced motor activity and seem to indicate a predominant role of A(2A) adenosine receptor in this effect.     

Adenosine A1 receptors and the anticonvulsant potential of drugs effective in the model of 3-nitropropionic acid-induced seizures in mice.

The role of adenosine A1 receptors in the activity of drugs and substances protecting against seizures evoked by mitochondrial toxin, 3-nitropropionic acid (3-NPA) was studied in mice. Non-selective A1/A2 adenosine receptor antagonist, aminophylline and selective A1 adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) diminished the anticonvulsive effects of diazepam, phenobarbital, valproate and gabapentin. In contrast, A1/A2 adenosine receptor antagonist, 8-(p-sulfophenyl)theophylline (8pSPT) not penetrating via blood-brain barrier was ineffective. Aminophylline and DPCPX but not 8pSPT also reversed the protective action of A1/A2 adenosine receptor agonist, 2-chloroadenosine (2-CADO) and selective A1 adenosine receptor agonist, R-N6-phenylisopropyloadenosine (R-PIA), against 3-NPA-evoked convulsions. Obtained results suggest that the central adenosine A1 receptor stimulation may play a role in the anticonvulsive potential of diazepam, phenobarbital, valproate and gabapentin in a novel model of 3-NPA-evoked seizures. Moreover, concomitant application of aminophylline with these drugs may reduce their clinical antiepileptic efficacy, especially among patients suffering from seizures related to the disturbances of mitochondrial respiratory chain.     

ATP modulates the release of noradrenaline through two different prejunctional receptors on the adrenergic nerves of rat prostate

1. The effects of adenosine and ATP receptor agonists on the release of endogenous noradrenaline from electrically stimulated (2 Hz, 0.1 msec) rat prostate were examined in order to clarify the pharmacological properties of prejunctional receptors for adenosine and ATP on the adrenergic nerve varicosities in the prostate. Noradrenaline was quantified by HPLC coupled with electrochemical detection techniques. 2. Both adenosine and ATP receptor agonists (1 micromol/L) inhibited noradrenaline release and the relative order of inhibitory effect was N(6)-cyclopentyl-adenosine (CPA) > 5'-N-ethylcarboxamidoadenosine > 2-chloroadenosine > adenosine > 2-methylthio-ATP (2mSATP) > AMP > ATP. 3. The adenosine receptor agonist CPA (1 nmol/L-1 micromol/L) and the ATP receptor agonist 2mSATP (100 nmol/L-100 micromol/L) inhibited the stimulation-induced release of noradrenaline in a concentration-dependent manner. The concentrations of CPA and 2mSATP that produced 50% inhibition of noradrenaline release were 9.6 nmol/L and 1.4 micromol/L, respectively. 4. 1,3-Dipropyl-8-cyclopentylxanthine, an adenosine A(1) receptor antagonist, significantly reduced the inhibitory effects of not only CPA, but also 2mSATP. 5. Suramin, an ATP receptor antagonist, significantly reduced the inhibitory effects of 2mSATP, but not those of CPA. 6. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid, another ATP receptor antagonist, had no effect on the inhibitory action of either agonist. 7. These results suggest that, in the sympathetic nerve terminals of rat prostate, adenosine and ATP induce inhibition of noradrenaline release via the activation of adenosine A(1) and/or xanthine-sensitive ATP receptors, which play an inhibitory regulatory role in adrenergic neurotransmission in the prostate.     

Alterations in blood levels of carbohydrate and lipid metabolites and of cyclic AMP mediated by beta1- and beta2-adrenoceptors in beagle dogs: effects of procaterol, a new selective beta2-adrenoceptor agonist.

The intravenous injection of isoprenaline (10 nmole/kg) into conscious beagle dogs caused significant increases in the blood level of lactate, glucose, FFA, insulin and cyclic AMP. These metabolic alterations induced by isoprenaline were blocked completely by pretreatment of the dog with propranolol (1 mg/kg). Butoxamine (10 mg/kg) antagonized isoprenaline-induced increases in glucose, lactate and insulin, but not the increases in FFA. Practolol (10 mg/kg) diminished the increase in blood FFA very strongly. Salbutamol, which is known to be an agonist of the beta 2-subtype in its bronchomotor and cardiovascular actions, produced marked increases in the blood concentrations of lactate, glucose and insulin but were without effect on the FFA level. Thus metabolic responses of conscious beagle dogs to beta-adrenoceptor agonists appeared to depend differentially on two types of beta-adrenoceptors: beta1-adrenoceptors are largely involved in lipolysis while beta2-adrenoceptors are involved in the regulation of blood glucose metabolism and insulin secretion. A new beta-adrenoceptor agonist, 5-(1-hydroxy-2-isopropylaminobutyl)-8-hydroxycarbostyril hydrochloride hemihydrate (Procaterol), was classified as a beta 2-agonist, because it markedly increased plasma concentrations of glucose, lactate and insulin but increased the plasma level of FFA to a lesser degree. The order of potency of beta2-agonists was procaterol greater than salbutamol greater than trimetoquinol. Metabolic responses of beagle dogs would be useful for appreciating the selectivity and potency of beta-adrenoceptor agonists and antagonists.     

Influence of the combined treatment of LY 300164 (an AMPA/kainate receptor antagonist) with adenosine receptor agonists on the electroconvulsive threshold in mice.

7-Acetyl-5-(4-aminophenyl)-8,9-dihydro-8-methyl-7H-1,3-dioxolo-4,5H-2,3-benzodiazepine hydrochloride (LY 300164; a selective noncompetitive AMPA/kainate antagonist; 2 mg/kg) and N(6)-2-(4-aminophenyl)ethyl-adenosine (APNEA; a nonselective adenosine A(1)/A(3) receptor agonist; 2 and 3 mg/kg) significantly raised the threshold for electroconvulsions in mice. In contrast, 5'-N-ethylcarboxamidoadenosine (NECA; a nonselective adenosine A(1)/A(2) receptor agonist; up to 1 mg/kg) did not affect the electroconvulsive threshold. The combined treatment of LY 300164 with NECA or APNEA was superior to single-drug medication as regards their protective action in this seizure model. Moreover, the combinations of LY 300164 with either NECA or APNEA were devoid of motor impairment, although they produced a significant long-term memory deficit. Measurement of the plasma levels of LY 300164 alone and in combination with APNEA or NECA did not suggest pharmacokinetic phenomena as an explanation for the interaction between these drugs. APNEA did not influence the plasma concentration of LY 300164. Moreover, NECA even significantly decreased the plasma levels of the AMPA/kainate antagonist. The present study clearly indicates a strong positive interaction in terms of anticonvulsant activity between LY 300164 and the drugs acting via adenosine receptors.     

2-Chloroadenosine, a preferential agonist of adenosine A1 receptors, enhances the anticonvulsant activity of carbamazepine and clonazepam in mice.

2-Chloroadenosine (0.25-1 mg/kg) significantly raised the threshold for electroconvulsions in mice. This preferential adenosine A(1) receptor agonist (at 0.125 mg/kg) significantly potentiated the protective activity of carbamazepine against maximal electroshock-induced seizures in mice. 2-Chloroadenosine (1 mg/kg) showed also anticonvulsive efficacy against pentylenetetrazol-evoked seizures, raising the CD(50) value for pentylenetetrazol from 77.2 to 93.7 mg/kg. The drug (at 0.5 mg/kg) significantly enhanced the protective action of clonazepam in this test, decreasing its ED(50) value from 0.033 to 0.011 mg/kg. Moreover, aminophylline, a non-selective adenosine receptor antagonist (5 mg/kg), and 8-cyclopentyl-1,3-dimethylxanthine (8-CPX), a selective A(1) adenosine receptor antagonist (5 mg/kg) reversed the 2-chloroadenosine (0.125 mg/kg)-induced enhancement of the protective activity of carbamazepine and clonazepam. 2-Chloroadenosine administered alone or combined with antiepileptic drugs, caused neither motor nor long-term memory impairment. Finally, the adenosine A(1) agonist did not change the free plasma concentration of antiepileptics, so a pharmacokinetic factor is not probable. Summing up, 2-chloroadenosine potentiated the protective activity of both carbamazepine and clonazepam, which seems to be associated with the enhancement of purinergic transmission mediated through adenosine A(1) receptors.     

The lipolytic effect of beta 1- and beta 2-adrenoceptor activation in healthy human volunteers.

1. We investigated the effect of activation beta 1- and beta 2-adrenoceptors on the process of lipolysis in human volunteers. Ten male subjects underwent a single-blind randomized cross-over trial using infusions of terbutaline (a specific beta 2-adrenoceptor agonist), xamoterol (a partial beta 1-agonist with beta 2-adrenoceptor blocking activity) and saline (placebo control). The effect of these infusions on plasma potassium, glucose, free fatty acids (FFA) (total and individual) and insulin levels was studied. 2. Terbutaline infusion induced a significant rise in plasma glucose and a fall in plasma potassium in keeping with its beta 2-adrenoceptor stimulant properties. Xamoterol infusion had no significant effect on these values. Terbutaline infusion caused a greater rise in total and individual FFA than xamoterol, but both effects were significantly different from placebo. 3. The possible reasons for these results and their implications on the beta-adrenergic control of lipolysis are discussed.     

Evidence for an atypical receptor mediating the augmented bronchoconstrictor response to adenosine induced by allergen challenge in actively sensitized Brown Norway rats

The bronchoconstrictor response to adenosine is markedly and selectively increased following ovalbumin (OA) challenge in actively sensitized, Brown Norway rats. We present a pharmacological analysis of the receptor mediating this response. Like adenosine, the broad-spectrum adenosine receptor agonist, NECA, induced dose-related bronchoconstriction in actively sensitized, OA-challenged animals. In contrast, CPA, CGS 21680 and 2-Cl-IB-MECA, agonists selective for A(1) A(2A) and A(3) receptors, respectively, induced no, or minimal, bronchoconstriction. Neither the selective A(1) receptor antagonist, DPCPX, nor the selective A(2A) receptor antagonist, ZM 241385, blocked the bronchoconstrictor response to adenosine. MRS 1754, which has similar affinity for rat A(2B) and A(1) receptors, failed to block the bronchoconstrictor response to adenosine despite blockade of the A(1) receptor-mediated bradycardia induced by NECA. 8-SPT and CGS 15943, antagonists at A(1), A(2A), and A(2B) but not A(3) receptors, inhibited the bronchoconstrictor response to adenosine. However, the degree of blockade (approximately 3 fold) did not reflect the plasma concentrations, which were 139 and 21 times greater than the K(B) value at the rat A(2B) receptor, respectively. Adenosine and NECA, but not CPA, CGS 21680 or 2-Cl-IB-MECA, induced contraction of parenchymal strip preparations from actively sensitized OA-challenged animals. Responses to adenosine could not be antagonized by 8-SPT or MRS 1754 at concentrations >50 times their affinities at the rat A(2B) receptor. The receptor mediating the bronchoconstrictor response to adenosine augmented following allergen challenge in actively sensitized BN rats cannot be categorized as one of the four recognized adenosine receptor subtypes.     

Selective agonist of group II glutamate metabotropic receptors, LY354740, inhibits tolerance to analgesic effects of morphine in mice

1. Antagonists of glutamate N-methyl-D-aspartate (NMDA) subtype receptor inhibit the development of tolerance to the antinociceptive effects of opioids. Another way to inhibit the function of glutamate receptors is the stimulation of presynaptic metabotropic group II (mGluRII) receptors. Because LY354740 ((+)-2-aminobicyclo [3,1,0] hexane-2,6-dicarboxylic acid) is the first systemically active agonist of group II mGlu receptors, we investigated if this compound might inhibit the development of tolerance to antinociceptive effects of morphine and fentanyl. 2. As assessed by cumulative dose-response approach in the tail-flick test, administration of 10 mg kg(-1) morphine bid s.c. to male Albino Swiss mice for 6 days, right-shifted morphine dose-response curve by approximately 4 fold. In a separate group of mice, 12 injections of 0.04 mg kg(-1) of fentanyl over 3 days, right-shifted fentanyl dose-response curve by approximately 3.3 fold. 3. In experiment 1, LY354740 (1 and 10, but not 0.1 mg kg(-1)) as well as the reference compound, an uncompetitive NMDA receptor antagonist memantine (7.5 mg kg(-1)) inhibited the development of morphine tolerance. Neither LY354740 (10 mg kg(-1)) nor memantine (7.5 mg kg(-1)) affected the development of tolerance to fentanyl. In experiment 2, neither LY354740 (1 and 10 mg kg(-1)) nor memantine (7.5 mg kg(-1)) affected the tail-flick antinociceptive response, or the acute antinociceptive effect of morphine. 4. The present results are the first to suggest that the development of antinociceptive morphine tolerance may be inhibited by metabotropic group II glutamate agonist.     

Possible role of mast cells in cineole-induced scratching behavior in mice.

We examined the scratch (itch) inducing effect of 1,8-cineole (cineole), a monoterpene oxide present in many plant essential oils and the possible role of mast cells in the response. Subcutaneous injection of cineole (10, 20 and 40 microl/site) or the mast cell degranulating agent, compound 48/80 (25, 50 and 100 microg/site) into the rostral back of mice induced a scratching behavior. This response of cineole as well as that of 48/80 was markedly suppressed in mice subjected to mast cell desensitization by repeated injections of 48/80. The cineole-induced scratching was also significantly diminished in animals pretreated with diphenhydramine, the histamine H1-receptor antagonist or cyproheptadine, the dual histamine/serotonin-receptor antagonist. Furthermore, the scratch-inducing effect of cineole was greatly reduced in mice that received the opioid antagonist naloxone or the selective adenosine A1-receptor agonist, N6-cyclopentyladenosine (CPA), but not the more selective adenosine A2-receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA). The data suggest a likely role for mast cells in cineole-induced scratching behavior of mice, possibly involving adenosinergic and opioidergic mechanisms.