Mast cell mediators in citric acid-induced airway constriction of guinea pigs

We demonstrated previously that mast cells play an important role in citric acid (CA)-induced airway constriction. In this study, we further investigated the underlying mediator(s) for this type of airway constriction. At first, to examine effects caused by blocking agents, 67 young Hartley guinea pigs were divided into 7 groups: saline + CA; methysergide (serotonin receptor antagonist) + CA; MK-886 (leukotriene synthesis inhibitor) + CA; mepyramine (histamine H1 receptor antagonist) + CA; indomethacin (cyclooxygenase inhibitor) + CA; cromolyn sodium (mast cell stabilizer) + CA; and compound 48/80 (mast cell degranulating agent) + CA. Then, we tested whether leukotriene C4 (LTC4) or histamine enhances CA-induced airway constriction in compound 48/80-pretreated guinea pigs. We measured dynamic respiratory compliance (Crs) and forced expiratory volume in 0.1 s (FEV0.1) during either baseline or recovery period. In addition, we detected histamine level, an index of pulmonary mast cell degranulation, in bronchoalveolar lavage (BAL) samples. Citric acid aerosol inhalation caused decreases in Crs and FEV0.1, indicating airway constriction in the control group. This airway constriction was significantly attenuated by MK-886, mepyramine, cromolyn sodium, and compound 48/80, but not by either methysergide or indomethacin. Both LTC4 and histamine infusion significantly increased the magnitude of CA-induced airway constriction in compound 48/80-pretreated guinea pigs. Citric acid inhalation caused significant increase in histamine level in the BAL sample, which was significantly suppressed by compound 48/80. These results suggest that leukotrienes and histamine originating from mast cells play an important role in CA inhalation-induced noncholinergic airway constriction.     

Effects of specific tachykinin receptor antagonists on citric acid-induced cough and bronchoconstriction in unanesthetized guinea pigs

We compared the effects of a tachykinin NK₁ receptor antagonist, FK888 (N²-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl)carbonyl- -prolyl]-N-methyl-N-phenylmethyl-3-(2-naphtyl)- -alaninamide), and a tachykinin NK₂ receptor antagonist, SR48968 ((S)-N-methyl-N[4-(4-acetylamino-4-phenyl-piperidino)-2-(3,4-dichlorophenyl)butyl]benzamide]), on citric acid-induced cough and bronchoconstriction in conscious guinea pigs. FK888 and SR48968 inhibited the cough dose dependently. Combination of FK888 and SR48968 showed a small additive effect compared with that of FK888 or SR48968 alone. SR48968 but not FK888 inhibited the bronchoconstriction dose dependently. These results indicate that tachykinin NK₁ receptors as well as tachykinin NK₂ receptors are involved in the citric acid-induced cough response. The antitussive activity of the tachykinin NK₁ receptor antagonist appeared not to depend on the anti-bronchoconstrictor effects.     

Pharmacological characterization of mediators and vagal influence in the acute allergic bronchoconstriction in guinea pigs

Summary The allergic bronchoconstriction in guinea pigs has been attributed mainly to the release of mast cell mediators. Histamine has been involved in the first minutes of the anaphylactic reaction and new-formed compounds in the subsequent response. In this asthma model the vagal influence has been sparsely investigated. In the present work we evaluated the pharmacological modification of the acute allergic bronchoconstrictor response in guinea pigs sensitized to ovalbumin through aerosol exposure. Pyrilamine (20 g/kg), diethylcarbamazine (a lipoxygenase inhibitor, 10 mg/kg) and dexamethasone (4 mg/kg) each reduced the antigen-induced bronchoconstriction throughout the 30 min studied. Indomethacin (3.1 mg/kg) did not modify the response to the antigen. Atropine (2 mg/kg) plus bilateral vagotomy also diminished this response from 5 min onward. On the other hand, from 5 min ahead pyrilamine-resistant bronchoconstriction was partially inhibited by dexamethasone, and it was almost completely blocked during all of the response when atropine plus bilateral vagotomy were added to dexamethasone. Dipyridamole (an inhibitor of the adenosine uptake, 0.4 mg/kg) enhanced the bronchoconstriction, though this was significant only in the 2–5 min time-interval of the response. These results suggest that histamine and vagal influence play an important role in the whole response to antigen, that other mediators, probably leukotrienes, participate in this response from 5 min onward, and that adenosine could exert a potentiation effect on this response. Send offprint requests to L. M. Montaño at the Instituto Nacional de Enfermedades Respiratorias     

Effects of eppikahangeto, a Kampo formula, and Ephedrae herba against citric acid-induced laryngeal cough in guinea pigs

To evaluate the efficacy of three common antitussive Kampo formulas, eppikahangeto (EPP), bakumondoto (BAK), and shoseiryutogomakyokansekito (SGM), a new cough model of guinea pig was used, which could specifically induce a laryngeal cough by microinjection of citric acid solution into the larynx. Kampo extract was dissolved in water and the animals were given access ad libitum for 3 days, and then the number of coughs during 10 min was counted. EPP extract decreased the number of coughs dose-dependently (0.3% extract, -22.9 +/- 6.6%, P<0.01; 1.0% extract, -32.4 +/- 5.5%, P<0.01). BAK extract and SGM extract had no significant effect. Intraperitoneal injection of codeine (60 mg/kg) also decreased the number of coughs (-36.1 +/- 9.1%, P<0.05). Furthermore, Ephedrae herba (EH) extract reduced the number of coughs (-18.3 +/- 6.0%, P<0.05), but the extract of EPP without EH did not. These results suggest that EPP has an antitussive effect against laryngeally-induced cough in guinea pigs, and the crucial herbal medicine is EH.     

Role of calcium in arachidonic acid-induced contractions of guinea pig airways

We have previously shown that arachidonic acid (AA)-induced contractions of indomethacin-pretreated guinea pig trachea and parenchyma are due to the synthesis of leukotrienes C4 and D4. The present experiments were designed to investigate the role of calcium (Ca2+) in the above. AA (66 microM)-induced contractions of trachea, but not parenchyma, were reduced in Ca2+-free Krebs-Henseleit solution ( KHS ). However the contractions of both trachea and parenchyma were abolished in Ca2+-free KHS with either lanthanum chloride (1 mM) or EDTA (300 microM). The Ca2+ antagonists, verapamil (100 microM), nitrendipine (100 microM), and TMB-8 (100 microM), reduced AA-induced contractions of both trachea and parenchyma. Re-addition of Ca2+ (2.2 mM) to trachea and parenchyma in Ca2+-free KHS in the presence of lanthanum restored the AA-induced contractions. This effect of Ca2+ was reduced by verapamil (100 microM) or nitrendipine (100 microM). LTC4-induced contractions of trachea and parenchyma were unaffected by nitrendipine (100 microM), whereas tracheal contractions were reduced in Ca2+-free KHS . Both tracheal and parenchymal contractions to LTC4 were reduced in Ca2+-free KHS in the presence of lanthanum chloride (1 mM). We conclude that superficially bound pools of Ca2+ are important in AA-induced contractions of the airways. Furthermore, nitrendipine reduces AA-induced contractions by inhibiting AA metabolism and not by inhibiting airway smooth muscle contraction induced by released leukotrienes.     

Role of substance P and tachykinin receptor antagonists in citric acid-induced cough in pigs

The purpose of this work was to investigate the role of tachykinins in cough induced by citric acid (0.8 M) in pigs. With this object, we have studied the effect of citric acid on substance P content in the tracheo-bronchial tree and the effects of substance P and of tachykinin receptor antagonists on citric acid-induced cough. Citric acid exposure significantly increased substance P concentration in both broncho-alveolar and tracheal lavage fluids, while it decreased significantly the substance P content in tracheal mucosa. Substance P did not elicit cough, but significantly potentiated the citric acid-induced cough frequency. Tachykinin NK(1), NK(2) or NK(3) receptor antagonists, SR 140333 (nolpitantium), SR 48968 (saredutant) and SR 142801 (osanetant), respectively, significantly inhibited citric acid-induced cough. The same inhibitory effect of tachykinin receptor antagonists was observed, when substance P was nebulised before citric acid challenge. We conclude that citric acid induces in pigs a release of substance P in the tracheo-bronchial tree, which plays a sensitising role on the cough reflex. The involvement of tachykinin NK(1), NK(2), NK(3) receptors are also demonstrated in this reflex.     

ATP-induced histamine release is in part related to Phospholipase A2- mediated arachidonic acid metabolism in rat peritoneal mast cells

Histamine and arachidonic acid (AA) release was measured using the P2-purinoceptor antagonists, phospholipase A2 (PLA2) and cyclooxygenase (COX)/lipoxygenase (LOX) inhibitors to determine whether or not ATP-induced histamine release is associated with arachidonic acid (AA) release in rat peritoneal mast cells. ATP increased histamine release in a dose dependent manner, whereas adenosine did not. PPADS (a selective P2X-purinoceptor antagonist) and suramin (a nonselective P2X,2Y-purinoceptor antagonist) inhibited ATP-induced histamine release in a dose dependent manner. However, RB-2 (a P2Y-purinoceptor antagonist) did not block ATP-induced histamine release. Manoalide and oleyloxyethyl phosphorylcholine (OPC), secretory PLA2 inhibitors, also inhibited ATP-induced histamine release dose-dependently. Both COX inhibitors (ibuprofen and indomethacin) and LOX inhibitors (baicalein and caffeic acid) inhibited ATP-induced histamine in a dose dependent manner. ATP significantly increased [3H]AA release by 54%. PPADS and suramin significantly inhibited ATP-induced [3H]AA release by 81% and 39%, respectively. ATP-induced histamine release was significantly inhibited by a variety of protein kinase inhibitors, such as bisindolmaleimide, genistein, methyl 2,5-dihydroxycinnamate, W-7 and trifluoperazine. Overall, the results suggest that ATP-induced histamine release is in part related to the PLA2-mediated AA metabolism and P2X-purinoceptors.     

Effects of inhaled alpha 2-adrenoceptor and GABAB receptor agonists on citric acid-induced cough and tidal volume changes in guinea pigs.

The effects of alpha 2-adrenoceptor and GABA receptor agonists on citric acid-induced cough and increased tidal volume were investigated in conscious guinea pigs. Inhalation of low doses of B-HT 920 (5-allyl-2-amino 5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepine dihydrochloride), and xylazine significantly inhibited citric acid-induced cough and tidal volume increases. Intraperitoneal administration of higher doses of B-HT 920 than those given by aerosol were ineffective. The inhibitory effects of B-HT 920 were antagonised by prior intraperitoneal administration of yohimbine, but not atropine. Inhalation of GABA or baclofen inhibited tidal volume increases, but had no effect on cough. Inhaled alpha 2-adrenoceptor or GABA agonists had no effect on the reduced respiratory rate after citric acid inhalation. It is concluded that alpha 2-adrenoceptor agonists inhibit cough via a mechanism which may not be related to their ability to reduce citric acid-induced tidal volume increases, since GABA and baclofen inhibited tidal volume increases but not cough. We suggest that alpha 2-adrenoceptor agonists may have therapeutic potential in the treatment of cough.     

Effects of TMK688, a novel anti-allergic drug, on allergic nasal obstruction and exudative responses in sensitized guinea pigs

TMK688 (1-[{5’-(3”-methoxy-4”-ethoxy-carbonyloxyphenyl)-2’,4’-pentadienoyl} aminoethyl]-4-diphenylmethoxypiperidine) is being developed as an orally effective antiallergic drug having both 5-lipoxy-genase inhibitory activity and anti-histamine activity (Shizawa et al. 1996; Tohda et al. 1997). The efficacy of TMK688 against allergic rhinitis was examined in passively sensitized guinea pigs. TMK688 inhibited the increase in intranasal resistance following antigen challenge at doses of 1 and 3.2mg/kg p.o. The allergic nasal obstruction was also suppressed by 10mg/kg i.v. of FPL-55712, a peptide leukotriene receptor antagonist, but not by 3.2mg/kg i.v. pyrilamine, a histamine H¹ receptor antagonist, or by 10mg/kg p.o. of ketotifen, an anti-allergic drug having anti-histamine activity, suggesting that the nasal obstruction was caused by leukotrienes. Following antigen challenge, the intranasal release of leukotrienes B₄ and C₄, and histamine increased in passively sensitized guinea pigs. TMK688 tended to suppress the increase in immunoreactive leukotrienes B₄ and C₄ in the nasal lavage fluid at a dose of 1mg/kg p.o., and significantly inhibited the increase at 3.2mg/kg. The brilliant blue dye leakage following antigen challenge from the blood stream into the na-sal cavities was significantly inhibited by not only TMK688 and FPL-55712 but also pyrilamine, suggesting that the allergic dye leakage was caused cooperatively by leukotrienes and histamine. However, keto-tifen showed no significant suppression of the dye leakage even at 10mg/kg p.o., although this drug inhibited the histamine-induced dye leakage at far lower doses (0.1mg/kg p.o. or higher) in unsensitized guinea pigs. Therefore, histamine is not necessarily the major mediator of allergic dye leakage in our experiment. These findings demonstrate that TMK688 may be superior to antihistamines as a therapeutic agent for allergic rhinitis. Received: 25 April 1997 / Accepted: 5 August 1997     

Studies on the release of histamine from isolated guinea pig mast cells stimulated by ionophore A23187 or by the anaphylactic reaction

Summary The divalent cation ionophore A23187 was found to produce a dose-dependent release of histamine from isolated mesenteric mast cells of the guinea pig. The process showed a specific requirement for calcium ions and was blocked by inhibitors of glycolysis.The effect of cAMP^**, theophylline, sympathomimetic amines and DSCG on the histamine release induced by the ionophore or by the antigen-antibody reaction was compared. In both cases, the release was inhibited by Bu₂cAMP and by theophylline but higher concentrations were required with the ionophore. Adrenaline, isoprenaline and DSCG were effective only in the anaphylactic system.These results are compared with those previously reported for human leucocytes and rat peritoneal mast cells in which the release produced by the ionophore was found not to be inhibited by cAMP and its analogues. On the basis of these findings, the possible role of cAMP in the modulation of histamine release is discussed.Parts of this work have been presented to the 18. Spring Meeting of the German Pharmacological Society, Mainz, March 1977     

Inhibiting effect of ammonia on citric acid-induced cough in pigs: a possible involvement of substance P

The effect of ammonia on the cough response to citric acid and on substance P release from C-fibers involved in this reflex was assessed. For a period from one to four days, piglets were exposed, in an inhalation chamber, to ammonia at a concentration of 15 or 30 ppm. During exposure, cough induction tests were done every two days. Recovery of the cough reflex after ammonia exposure was also determined. In a separate group of piglets exposed for 2 days to 30 ppm ammonia, substance P content was determined in bronchial and tracheal lavage fluids and in the tracheal and bronchial mucosa. Ammonia (30 ppm) was found to inhibit coughing significantly (the cough frequency was reduced by 64%) after a two-day exposure. In animals exposed for 4 days to this ammonia concentration, the recovery ranged from 3 to 7 days (mean: 5 days). The same ammonia concentration also caused the substance P content to increase significantly in bronchoalveolar lavage fluid (to 432% of its initial value) and tracheal lavage fluid (to 149%) and to decrease significantly in the tracheal mucosa (-58%), however the content in bronchial mucosa was not significantly affected (-43%). Exposure to 15 ppm ammonia had no effect on the frequency of citric acid-induced coughing. In conclusion, ammonia inhibits citric acid-induced coughing in pigs at concentrations that can be detected in piggeries. This inhibitory effect may be related to substance-P depletion in C-fiber endings.     

N-(3’,4’,5’-三甲氧基肉桂酰)邻氨基苯甲酸对抗原诱发的离体豚鼠回肠收缩、大鼠肥大细胞脱颗粒及组胺释放的影响

实验证明 N-(3′,4′,5′-三甲氧基肉桂酰)邻氨基苯甲酸(TOA)管内浓度80μg/ml 能明显抑制抗原诱发的主动致敏豚鼠离体回肠收缩。TOA 管内浓度25和50μg/ml 能显著抑制亲同种细胞抗体介导的大鼠肠系膜肥大细胞脱颗粒和腹腔肥大细胞组胺释放。     

N—（3′，4′，5′—三甲氧基肉桂酰）邻氨基苯甲酸对抗原诱发的离体豚鼠回肠收缩、大鼠肥大细胞脱颗粒及组胺释放的影响

实验证明N－（3′，4′，5′－三甲氧基肉桂酰）邻氨基苯甲酸（TOA）管内浓度80μg/ml能明显抑制抗原诱发的主动致敏豚鼠离体回肠收缩。TOA管内浓度25和50μg/ml能显著抑制亲同种细胞抗体介导的大鼠肠系膜肥大细胞脱颗粒和腹腔肥大细胞组胺释放。     

Histamine catabolism in guinea pigs, rats and mice

Histamine catabolism in vivo was studied in unanesthetized rats and guinea pigs; tissues from animals sacrificed 10 min after s.c. injection of ¹⁴C-histamine were assayed for ¹⁴C-histamine and total ¹⁴C. Groups pretreated with aminoguanidine, a diamine oxidase inhibitor, and methylhistamine, an inhibitor of the histamine-methylating enzyme, were used to evaluate roles of these enzymes in individual tissues. For rats the data suggested presence of both enzymes in intestine, diamine oxidase in lung and liver, methylation in kidney, and marked ability of heart to extract ¹⁴C-histamine from blood; these results closely check earlier data from tissues of anesthetized rats sacrificed 2.5 min after i.v. injection of ¹⁴C-histamine. For guinea pigs intestine showed evidence for both enzymes, liver and kidney for diamine oxidase, and lung and heart, for methylation. Since in animals injected with ¹⁴C-histamine, aminoguanidine pretreatment sharply reduced total ¹⁴C in mouse intestine and rat liver, another diamine oxidase inhibitor was tested; similar results were obtained. Amodiaquine, a strong inhibitor of histamine methylation in vitro, was found to inhibit in vivo. Catabolism of endogenously formed ¹⁴C-histamine was tested in the female rat, an animal which destroys exogenous histamine largely through the diamine oxidase pathway. Rats pretreated with aminoguanidine and then injected with ¹⁴C-L-histidine, excreted only slightly more ¹⁴C-histamine in urine than did controls. The ineffectiveness of aminoguanidine suggests that even in the female rat, diamine oxidase may have little significance in local catabolism of newly formed histamine. Possible reasons are discussed.     

Adenosine triphosphate levels during anaphylactic histamine release in rat mast cells in vitro. Effects of glycolytic and respiratory inhibitors.

The adenosine triphosphate (ATP) content of rat mast cells was studied during and after anaphylactic histamine release. The almost identical time course of ATP decrease from mast cells treated with either glycolytic or respiratory inhibitors supports the view that the ATP depletion was largely related to the histamine release process and not to an uncoupling of oxidative phosphorylation by an increased concentration of cytosol Ca2+. The ATP content of the cells was not restored within the 2 h of observation. No inhibition of lactate production from mast cells exposed to antigen in the presence of respiratory inhibitors and glucose was observed. Based on the lactate production from mast cells, the turnover time of ATP was calculated to be about 3/4 min.     

杠柳苷元对肥大细胞脱颗粒及释放组胺影响的研究

目的:研究香加皮提取单体化合物杠柳苷元对大鼠和小鼠肥大细胞脱颗粒及组胺释放的影响。方法:大鼠腹腔注射百日咳疫苗、后腿注射卵白蛋白致敏,用于测定肥大细胞脱颗粒反应及制备抗血清;取致敏大鼠的血清稀释后对小鼠进行腹腔注射,测定肥大细胞脱颗粒反应;以荧光分光光度法测定组胺浓度。结果:杠柳苷元对体外培养肥大细胞的组胺释放有显著的抑制作用,实验剂量即可使组胺释放浓度降低(69.4±8.6)%,其抑制作用呈显著的剂量依赖关系;杠柳苷元对抗原致敏大鼠肥大细胞的组胺释放也有显著的抑制作用,在20μg·mL-1浓度时即可使组胺释放浓度减少73.55%;杠柳苷元口服给予致敏小鼠后,在50mg·kg-1剂量时即可使小鼠组胺释放浓度减少80%以上,并呈显著的剂量依赖关系。结论:杠柳苷元对体外培养的肥大细胞、致敏大鼠肥大细胞的组胺释放有显著的抑制作用;口服给予杠柳苷元可使小鼠显著减少肥大细胞的组胺释放。鉴于肥大细胞脱颗粒及组胺释放在炎症反应中的作用,可认为杠柳苷元是香加皮具有抗炎作用的有效成分之一。     

Catecholamine release during anaphylactic shock in guinea pigs

Summary In the acute anaphylactic as well as histamine shock of guinea pigs an increase of the serum catecholamines was found. Mepyramine doses high enough to abolish the anaphylactic bronchospasm did not prevent the catecholamine release, but reduced it. When the anaphylactic bronchoconstriction was inhibited by mepyramine, mean serum adrenaline concentrations 20 min after antigen were as high as in acute anaphylactic shock without administration of antihistamines; 120 min after antigen no increases was seen. In animals which died in the so-called protracted anaphylactic shock the serum adrenaline concentrations were the highest found at all. The results are discussed in view of the role of catecholamines in anaphylaxis.Supported by the Deutsche Forschungsgemeinschaft.     

Antitussive effect of NS-398, a selective cyclooxygenase-2 inhibitor, in guinea pigs

Several reports have demonstrated that the number of capsaicin-induced coughs is increased in the presence of prostaglandins in the airway. Moreover, it has been reported that the expression of cyclooxygenase-2, which converts arachidonic acid to prostaglandins, was found in cultured human airway epithelial cells in the absence of inflammatory cytokine stimulation. Thus, it is possible that cyclooxygenase-2 inhibitor may produce an antitussive effect. To test this hypothesis, we investigated the effects of N-[2-(cyclohexyloxy)-4-nitrofenyl]-methane sulfonamide (NS-398), a selective cyclooxygenase-2 inhibitor, and 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethyl-pyrazole (SC-560), a selective cyclooxygenase-1 inhibitor, on capsaicin-induced coughs in guinea pigs. NS-398 (1-10 mg/kg, p.o.) dose-dependently and significantly reduced the number of capsaicin-induced coughs. In contrast, SC-560 (10 mg/kg, p.o.) did not reduce the number of capsaicin-induced coughs. The antitussive effect of NS-398 (10 mg/kg, p.o.) was not antagonized by pretreatment with methysergide (3 mg/kg, i.p.), a non-selective serotonin (5-HT) receptor antagonist, or glibenclamide (10 mg/kg, i.p.), an ATP-sensitive K(+) channel blocker. Furthermore, although NS-398 did not significantly affect the cough reflex induced by substance P (10(-16) M), it significantly reduced the capsaicin-induced release of substance P in bronchoalveolar lavage fluid (BALF). The present findings clearly show that cyclooxygenase-2 inhibitor, but not cyclooxygenasez-1 inhibitor, has a potent antitussive effect. Furthermore, it is possible that the antitussive action of NS-398 does not depend on centrally acting mechanisms, since 5-HT receptors play an important role in the cough-depressant activities of centrally acting antitussive drugs. NS-398 may exert peripheral antitussive effects by inhibiting the release of substance P from capsaicin-sensitive afferent C-fibers in the airways. These results suggest that cyclooxygenase-2 inhibitors may have a therapeutic benefit in reducing coughs.     

Mast cells reduce survival of myenteric neurons in culture

Mast cell-nerve interactions play a key role in intestinal inflammation and irritable bowel disease. Loss of enteric neurons has been reported in inflammatory conditions but the contribution of mast cells in this event is unknown. To study neuronal survival and plasticity of myenteric neurons in contact with mast cells a co-culture system using myenteric neurons from rat small intestine and peritoneal mast cells was set up.Dissociated myenteric neurons were cultured for 4 days before addition of mast cells isolated by peritoneal lavage. Neuronal survival and expression of vasoactive intestinal peptide (VIP) and nitric oxide synthase (NOS) were studied by immunocytochemistry and neuronal cell counting. Myenteric neurons cultured without mast cells were used to study the rate of neuronal survival after the addition of various mast cell mediators, proteinase-activated receptor₂ (PAR₂) agonist, VIP or corticosteroid.A striking mast cell-induced neuronal cell death was found after co-culturing. It was counteracted by the addition of mast cell stabiliser doxantrazole, protease inhibitors, PAR₂ antagonist FSLLRY-amide, corticosteroid or VIP. In myenteric neurons cultured without mast cells the PAR₂ agonist SLIGRL-amide, prostaglandin D₂ and interleukin (IL) 6 reduced neuronal survival while histamine, serotonin, heparin, IL1β and tumour necrosis factor α had no effect; corticosteroid and VIP enhanced neuronal survival. The relative numbers of VIP-, but not NOS-expressing myenteric neurons increased after co-culturing.Mast cell-induced neuronal cell death is suggested to be mediated via PAR₂ activation, IL6 and prostaglandin D₂. Corticosteroid and VIP are neuroprotective and able to prevent cell death of myenteric neurons in co-culture.     

Dual actions of adenosine on rat peritoneal mast cells

Summary The effects of adenosine and its analogues on cAMP-responses and histamine release of rat peritoneal mast cells were investigated. The adenosine analogue 5-N-ethylcarboxamidoadenosine (NECA') activates the adenylate cyclase of the mast cell membranes and elevates the cAMP-levels of the intact mast cells. Both effects are antagonized by methylxanthines, suggesting that they are mediated via an A₂ adenosine receptor. Adenosine and its analogues enhance the release of histamine from these cells, when the release is stimulated either by the calcium ionophore A 23187 or by concanavalin A. However, this effect is not antagonized by theophylline or 8-phenyltheophylline. In contrast, it is antagonized by the adenosine uptake blockers S-(p-nitrobenzyl)-6-thioinosine (NBTI) and S-(p-nitrobenzyl)-6-thioguanosine (NBTG). It is concluded that adenosine has two different effects on mast cells: it activates adenylate cyclase via an A₂ adenosine receptor, and it enhances histamine release via an action at an intracellular site.Abbreviations NECA 5-N-ethylcarboxamidoadenosine - NBTI S-(p-nitrobenzyl)-6-thioinosine - NBTG S-(p-nitrobenzyl)-6-thioguanosine - PIA N⁶-phenylisopropyladenosine - Con A concanavalin A Send offprint requests to M. J. Lohse at the above address