Influence of methoctramine on the acetylcholine-isoprenaline functional antagonism in the guinea pig isolated trachea

Summary— It has been suggested that activation of muscarinic M₂ receptors is one of the components of the functional antagonism between muscarinic and β-adrenoceptor agonists in canine and guinea pig tracheal smooth muscle. The aim of the present study was to determine in the guinea pig trachea the importance of this component according to the magnitude of the acetylcholine-induced contraction. Cumulative concentration-response curves for isoprenaline were obtained in the absence or presence of the muscarinic M₂ receptor antagonist methoctramine (3 × 10^?7 M) in tracheal rings under basal tension or precontracted by acetylcholine 2 × 10^?7, 3 × 10^?6 and 10^?4 M, giving contractions of 25, 50 or 75%, respectively, of the maximal tension induced by acetylcholine 3 × 10^?3 M. In the absence of methoctramine, acetylcholine induced a concentration-dependent shift of the concentration-response curves of isoprenaline (-log EC₅₀ of isoprenaline are 8.09 ± 0.07, 7.85 ± 0.08, 7.38 ± 0.12 and 6.49 ± 0.12, n = 6 for basal tension and for acetylcholine concentrations of 2 × 10^?7, 3 × 10^?6 and 10^?4 M, respectively). In the presence of methoctramine, the basal -log EC₅₀ of isoprenaline was unmodified, whereas the acetylcholine-induced shifts of concentration-response curves of isoprenaline were abolished for low levels of contraction (25%) and significantly reduced to 50 and 75% levels of contraction. Under similar conditions, acetylcholine-induced shifts of concentration-response curves of isoprenaline were unmodified by the muscarinic M₁ receptor antagonist pirenzepine (10^?7 M). These results suggest that the inhibitory effect of M₂ receptors on β-adrenoceptor agonists effects is important for low contraction levels induced by acetylcholine, and that this effect becomes less important for higher concentrations of acetylcholine.     

Influence of diazepam, alpidem, zolpidem and zopiclone, on the response to adenosine of the guinea pig isolated trachea

It has been reported that dipyridamole and some benzodiazepines potentiate the responses to adenosine in peripheral organs and in particular in the guinea pig isolated atria or trachea by inhibition of adenosine uptake and/or metabolism. In this study, we have examined the sensitization of guinea pig isolated trachea to relaxant responses to adenosine produced by dipyridamole, diazepam and 3 compounds chemically unrelated to benzodiazepines but which display selective agonistic activity towards the central (zolpidem and zopiclone) or peripheral (alpidem) type benzodiazpine receptors. In preparations under spontaneous tone and in the absence of adenosine, dipyridamole (10(-5) M) and diazepam (10(-5)-10(-4) M), alpidem (3 x 10(-6) M-10(-5) M) and zopiclone (10(-6)-10(-4) M) induced a relaxation of the airway smooth muscle. In addition, dazepam (10(-4) M) attenuated the phasic response to histamine (10(-5) M). Dipyridamole (10(-5) M) and diazepam (10(-4) M) respectively produced a 56.2 and 32.4-fold potentiation of adenosine relaxant effects. Alpidem (10(-6)-10(-5) M), zolpidem (10(-6)-10(-4) M) and zopiclone (10(-6)-10(-4) M) were without any significant effect on the adenosine concentration-response curves. Moreover, alpidem, zolpidem, and zopiclone did not modify the 2-chloroadenosine dose-response curves nor the diazepam induced sensitization of adenosine-induced relaxation. In conclusion, adenosine sensitization of the guinea pig isolated trachea caused by diazepam might involve a peripheral benzodiazpine receptor subtype coupled to a nucleoside transporter system which is different from those recognized by compounds derived from the imidazopyridine series.     

Smooth muscle relaxant activity of A1- and A2-selective adenosine receptor agonists in guinea pig trachea: involvement of potassium channels

Summary— The relaxant activities of N⁶-cyclopentyladenosine (CPA), an A1-selective agonist, and of 5′-(N-cyclopropyl)-carboxamidoadenosine (CPCA), a potent A2-receptor agonist, in the carbachol-contracted guinea pig isolated trachea have been evaluated. Both CPA and CPCA induced concentration-dependent relaxations of the guinea pig trachea, CPCA demonstrating a more potent but less efficient activity. 8-Cyclopentyl-1,3-dimethylxanthine (CPT) and 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (10 μM), both selective and potent A1-adenosine receptor antagonists, induced only a weak inhibition of CPA while 3,7-dimethyl-1-propargylxanthine (DMPX) (10 μM), a selective A2-adenosine receptor antagonist, failed to antagonize the relaxant activity of CPA. These results indicate that a major component of the tracheal relaxant activity of CPA occurred by a mechanism which is insensitive to the antagonist potency of A1- and A1-xanthine adenosine antagonists and therefore was not mediated by A1- or A1-adenosine receptors activation. The relaxant activity of CPCA was inhibited by DMPX, which supported the involvement of A2-adenosine receptors. Glibenclamide (10 μM), an inhibitor of K_ATP-channels, inhibited the relaxant activity of CPCA, whereas it was without effect on CPA. Iberiotoxin (180 nM), an inhibitor of the large-conductance CA2+-activated K+ channel, inhibited the relaxant action of CPA and CPCA. However, verapamil can offset the inhibition of CPA provided by iberiotoxin which suggests that such an antagonism does not represent an interaction between the toxin and CPA at the level of the large-conductance CA2+-activated K+-channel gating but rather functional antagonism attributable to the promotion of CA2+ influx by the toxin. In contrast, verapamil only partially reversed the inhibition of CPCA relaxant activity provided by iberiotoxin. Taken together, these results suggest that A2-adenosine receptor subtypes are coupled to KATP-channels and large-conductance CA2+-activated K+-channels in the guinea pig trachea whereas the unidentified adenosine receptor subtype, involved in CPA relaxant activity, is not.     

Salbutamol potentiates the relaxant effects of selective phosphodiesterase inhibitors on guinea pig isolated trachea

Summary— The ability of low concentrations of salbutamol to potentiate the relaxant effects of the phosphodiesterase (PDE) inhibitors, rolipram, Ro 20–1724 (PDE type IV inhibitor), siguazodan and milrinone (PDE type III inhibitor) was studied on guinea pig isolated trachea. These PDE inhibitors were strong relaxants of guinea pig trachealis under basal tone, but had only a weak activity on tissues precontracted with histamine (10^?5 M). In both cases, PDE type IV inhibitors showed a relaxant effect composed of two phases. The first phase represented 20 and 40% and the second, 90 and 140%, respectively, of relaxation of basal tone and histamine-induced tone. A second characteristic of PDE type IV inhibitors was the very fast and partially reversible relaxation observed at concentrations greater than 3 × 10^?8 M (for histamine-induced tone) at the first addition of inhibitor, followed by a residual relaxant activity. The latter relaxant effect was stable at concentrations of 3 × 10^?8-10^?5 M and was equivalent to a 20% relaxation (for histamine-induced tone). In the presence of low concentrations (10^?9 and 10^?8 M) of salbutamol, there was a significant concentration-dependent potentiation of the effects of PDE inhibitors on trachea precontracted with histamine. Salbutamol, at a concentration of 10^?9 M, potentiated the effects of PDE inhibitors between 1.4- and 3.6-fold. In the presence of salbutamol 10^?8 M, the potentiation was more marked for siguazodan (37.9-fold), milrinone (11.0-fold) and Ro 20–1724 (14.5-fold) than for rolipram (4.3-fold). These results suggest that low concentrations of salbutamol can potentiate the relaxant effects of both PDE type III and PDE type IV inhibitors. Thus, PDE type IV inhibitors, which have antiinflammatory properties, could also provide adequate bronchodilation when used in combination with lower than usual doses of β₂-agonists.     

Failure of aerosolized endothelin (ET-1) to induce bronchial hyperreactivity in the guinea pig

Aerosol administration of endothelin (ET-1) has been shown to provoke a potent bronchoconstriction in the guinea pig. We investigated whether or not, aerosolized ET-1 induces a bronchial hyperreactivity in the guinea pig. Aerosolized ET-1 (10 micrograms/ml for 60 min) did not alter the dose-response curve, established by successive aerosol administration of acetylcholine (ACh) 3-4 h and 18-24 h after challenge with the peptide. In a second protocol, aerosolized ET-1 (10 micrograms/ml for 3 min) induced, in anaesthetized guinea pigs a bronchopulmonary response but did not alter the dose-response curve to aerosolized ACh established 30 min after the challenge. These results suggest that ET-1 may participate to the early, but not the late alteration of the bronchopulmonary tone observed during pathophysiological conditions.     

Synergistic actions of pentobarbital and dihydropyridine Ca2+ antagonists on guinea pig isolated thoracic aorta†

Summary— In order to elucidate the mechanism(s) behind the interactions between barbiturates and Ca²⁺ antagonists, the effects of pentobarbital combined with three structurally diverse types of Ca²⁺ antagonist on CaCl₂-induced contractile responses of the guinea pig thoracic aorta in Ca²⁺-free and 40 mM K⁺ medium and the effects of pentobarbital on Ca²⁺ antagonist binding to guinea pig aortic membranes were investigated. The dihydropyridine derivatives isradipine (10^?10–10^?8 M) and nifedipine (10^?10–10^?8 M) inhibited CaCl₂-induced contractions concentration-dependently. Treatment with both pentobarbital (10^?4 M) and dihydropyridine Ca²⁺ antagonists (10^?9 M) shifted the CaCl₂ concentration-response curves to the right significantly compared with those after treatment with the Ca²⁺ antagonists and pentobarbital alone. However, no synergistic effects of pentobarbital (10^?4 M) with other types of Ca²⁺ antagonist (verapamil (10^?7 M) and diltiazem (10^?6 M)) were observed. The binding of [³H]isradipine (2 × 10^?9 M) to guinea pig aortic membranes was increased significantly by simultaneous pentobarbital treatment, but no such effect was observed with [³H]verapamil (10^?8 M) or [³H]diltiazem (2 × 10^?8 M). These findings suggest that the synergistic contractile effects of pentobarbital and dihydropyridines were, in part, due to enhancement of dihydropyridine binding to guinea pig aortic membranes (L-type Ca²⁺ channels) by pentobarbital and that the interactions between pentobarbital and Ca²⁺ antagonists may be structurally specific.     

Glucocorticoid modulation of muscarinic and β-adrenergic receptors in guinea pig lung

Summary— We investigated the effect of the in vivo treatment of guinea pigs with methylprednisolone, 10 mg/kg daily, on lung muscarinic and β-adrenergic receptors. Receptor densities were assessed by saturation experiments of tritiated N-methylscopolamine and dihydroalprenolol binding to lung membranes. After 3 h of treatment, methylprednisolone induced a decrease of 19.2% ( P < 0.05) of muscarinic receptors but was without effect on β-adrenergic receptor density. After 24 h, an increase of 39.7% ( P < 0.01) and 16.9% ( P < 0.05) was observed for muscarinic and β-adrenergic receptors, respectively. For muscarinic receptors, this increase reached 53.4% ( P < 0.01) within 48 h and stayed at this level until 96 h. The increase of β-adrenergic receptors was maximal (24.9%) after 72 h and returned to the control value after 96 h. The dissociation constant (K_d) values of both ligands were not affected by the glucocorticoid treatment. Functional studies showed that the 96 h treatment did not affect the contractile response of guinea pig lung parenchymal strips to carbachol since the 50% concentration value (EC₅₀) and the maximal contraction value (E_max) were not significatively different from control values. These data show that glucocorticoids control the expression of both muscarinic and β-adrenergic receptors in guinea pig lung but with different time courses and to a larger extent for muscarinic receptors. The glucocorticoid treament did not modify the contractile response of lung strips to carbachol, confirming the absence of effect on the affinity of muscarinic receptors and suggesting that the receptor reserve exceed the increase of their density by the steroid.     

Studies on the relationship between contraction and mediator release produced by ovalbumin in superfused trachea isolated from the actively sensitized guinea pig

The temporal relationship between release of the mediators histamine and slow reacting substance of anaphylaxis (SRS-A) and smooth muscle contraction in response to antigen was examined using superfused tracheae from actively sensitized (ovalbumin) and reserpine-pretreated guinea pigs. Maximum contraction occurred simultaneously with the maximum amount of histamine appearing in the superfusate, but the dose-response curves of ovalbumin were different for the two responses. The peak appearance of SRS-A in the superfusate was more delayed than that of peak histamine or contraction. After antigen-induced desensitization, histamine and SRS-A release evoked by rechallenge with antigen were reduced to a greater extent than was contraction. Indomethacin, 5 X 10(-6) M, did not alter mediator release but enhanced the height of contraction produced by a submaximum concentration of ovalbumin and impeded return to basal tension, 5,8,11,14-Eicosatetraynoic acid, 10(-5) M, in combination with indomethacin reduced the magnitude of this contraction and reduced by 50% the total SRS-A released without altering histamine release. 5,8,11,14-Eicosatetraynoic acid increased the magnitude of contraction observed after desensitization without altering mediator release. Addition of mepyramine, 10(-6) M, and FPL55712, 10(-5) M, to the superfusion solution reduced the magnitude of the contractions produced by ovalbumin in the absence of prior desensitization but had no effect on the contractions produced after desensitization. Histamine release was unaltered by these treatments. Although histamine and SRS-A appear to play a role in airway smooth muscle contraction, other unidentified mediator(s) may also be involved in the contractile response to antigen, especially after desensitization.     

Characterisation of left ventricular relaxation in the isolated guinea pig heart

The time constant of left ventricular pressure fall, τ, has frequently been used as a measure of myocardial relaxation in the blood-perfused, ejecting heart. The aim of the present study was to characterise τ in relation to β-adrenergic activation, coronary perfusion pressure and flow as well as cardiac oxygen supply and demand in the isolated, isovolumically beating heart. Therefore, τ was analysed from digitised left ventricular pressure data in a total of 23 guinea pig hearts perfused with saline at constant pressure (60 cmH₂O). The coronary venous adenosine concentration ([ADO]) served as an index of myocardial oxygenation. Isoprenaline (0.4–3.2 nmol l⁻¹) decreased and propranolol (3–9 μmol l⁻¹) increased τ dose-dependently (linear regression τ vs lg ([isoprenaline]),r=0.74; τ vs. lg([propranolol]),r=0.66, bothP<0.05). During graded reductions in cardiac oxygen supply from 96.1±12.6(SEM) to 44.4±4.4 μl min⁻¹ g⁻¹, τ was prolonged from 61.5±12.7 to 109.9±22.6 ms while left ventricular developed pressure (LVDP) decreased from 90.7±7.2 to 40.7±5.1 mmHg. In parallel, [ADO] increased from 23.7±9.1 to 58.0±19.1 pmol ml⁻¹ (P<0.05). Increasing oxygen supply to 165.4±32.4 μl min⁻¹ g⁻¹ augmented LVDP to 102.7±7.3 mmHg but did not change τ or [ADO]. There was a dual response of τ to changes in cardiac oxygen supply or demand. As long as oxygen supply and demand matched, τ remained constant. However, when the oxygen supply was less than 100 μl min⁻¹g⁻¹, left ventricular relaxation was prolonged in parallel to the reduction in oxygen supply. In addition, a close relationship was observed between [ADO] as an indicator of myocardial oxygenation and τ (Spearman correlation,r=0.99,P<0.005). We conclude that the time constant of left ventricular pressure fall, τ, sensitively reflects myocardial relaxation in the isolated, isovolumically beating guinea pig heart. Moreover, in this model left ventricular relaxation is not influenced by alterations in coronary perfusion pressure or flow as long as cardiac oxygen demand is matched by an adequate supply. Rather, relaxation is strictly coupled to myocardial oxygenation as reflected by coronary venous adenosine concentrations.     

雌性激素对妊娠豚鼠胆囊运动功能影响的实验研究

目的:探讨妊娠情况下雌性激素对豚鼠胆囊运动功能的影响及对胆囊结石形成的作用。方法:60只雌性豚鼠随机分为实验组(40只)和对照组(20只),实验组建立妊娠豚鼠动物模型,分为妊娠30d组和妊娠60d组,采用化学发光法和酶联亲和抗体组织化学法分别进行血清雌二醇(E2)、孕酮(Pg)浓度检测及胆囊组织雌激素受体(E R)、孕激素受体(PR)的检测,同时测量各组豚鼠胆囊空腹体积(FV),胆囊空腹胆汁量(FB)的变化,并观察胆囊结石形成情况。结果:妊娠60d组豚鼠有3只形成胆囊结石,妊娠豚鼠血清E2、Pg含量,胆囊组织E R、PR阳性表达率均明显高于非孕豚鼠(P<0.001),且随妊娠期进展而呈逐渐升高趋势。妊娠60d组豚鼠FV及FB明显大于妊娠30d组和对照组(P<0.001)。结论:妊娠期血清E2和Pg含量显著升高,诱发胆囊运动功能下降,胆囊胆汁淤积,是妊娠期胆囊结石形成的重要原因。     

Effect of removal of epithelium on antigen-induced smooth muscle contraction and mediator release from guinea pig isolated trachea

We examined the effect of removal of the epithelium on antigen-induced smooth muscle contraction and the release of mediators of inflammation from superfused, sensitized guinea-pig tracheal spirals in vitro. The epithelium was stripped from one-half of each trachea by mechanical means, and immunologic responses were evaluated by paired analysis. Removing the epithelium potentiated antigen-induced contraction, as reflected by a 5-fold leftward shift in the antigen dose-response curve, but the maximum response to antigen was not altered. This potentiation was not inhibited by pretreating the tissues with indomethacin (5 X 10(-6) M). At maximum concentrations of antigen removing the epithelium had no effect on the magnitude or kinetics of release of immunoreactive sulfidopeptide leukotrienes, prostaglandin (PG) D2, PGF2 alpha or thromboxane B2. Removing the epithelium did, however, significantly decrease the release of PGE and 6-keto-PGF1 alpha, a prostacyclin metabolite. Antigen-induced histamine release was enhanced by removing the epithelium; this effect varied inversely with antigen concentration. Selectively exposing either the luminal or serosal surface of an intact, superfused trachea to antigen resulted in the release of less than 5% of the total tissue histamine. Removing the epithelium from the intact trachea increased histamine release to approximately 25% following luminal but not serosal exposure to antigen. These studies demonstrate that the tracheal epithelium can act to inhibit antigen-induced airway contraction in vitro. This may in part reflect the role of the intact epithelium as a diffusion barrier which can limit the rate of influx of antigen molecules and thereby influence tissue mast cell activation.     

The calcium sensitizer levosimendan attenuates endotoxin-evoked myocardial dysfunction in isolated guinea pig hearts

Objective Sepsis-evoked myocardial dysfunction is possibly due to decreased myofilament calcium sensitivity, and a calcium sensitizer may thus specifically improve contractility in sepsis by enhancing myofilament calcium sensitivity. We examined whether the calcium sensitizer levosimendan mitigates myocardial dysfunction and improves contractility in hearts isolated from endotoxin-treated guinea pigs.Design and setting Prospective, controlled, randomized animal study in a university research laboratory.Subjects Guinea pig hearts isolated 4 h (n=10) or 18 h (n=8) following E. coli LPS (4 mg/kg i.p.) and hearts from sham-treated controls (n=11 and n=6).Interventions Isolated hearts were perfused at constant aortic pressure [Krebs-Henseleit buffer, heart rate: 300/min, left ventricular (LV) diastolic pressure: 6–8 mmHg], and LV developed pressure (LVdP) and LVdP/dt were continuously assessed. Levosimendan was added to the perfusate in incremental concentrations (0.03, 0.1, 0.3 µM).Measurements and results Endotoxin resulted in a significant decrease in LVdP by 20±6% and 43±8%, in +LVdP/dt by 16±5% and 44±7%, and in –LVdP/dt by 27±8% and 47±8% after 4 and 18 h, respectively. In septic hearts levosimendan increased LV function concentration-dependently by 32±4% (LVdP), 33±5% (+LVdP/dt), and 37±7% (–LVdP/dt) 4 h and by 31±6% (LVdP), 33±6% (+LVdP/dt), and 32±7% (–LVdP/dt) 18 h after LPS. However, levosimendan increased myocardial function similarly in control hearts.Conclusions While the calcium sensitizer levosimendan markedly improved LV contractility in hearts from both endotoxic and sham animals, it failed to specifically abolish endotoxin-evoked myocardial dysfunction. Thus, decreased calcium sensitivity either does not play a major role in endotoxin-evoked cardiomyopathy or the location of its pathomechanism differs from levosimendan's site of action.     

Phasic responses to carbachol in isolated guinea pig trachea are augmented by cooling and inhibited by nifedipine.

Steady-state and kinetic approaches were used to study the effects of cooling to 25 degrees C and nifedipine (1 microM) on the phasic and tonic responses to 0.3 and 10 microM carbachol (Carb) in isolated segments of epithelium-free guinea pig trachea. Cooling and nifedipine had no effect on the steady-state tensions of the contractile responses to Carb in Krebs-bicarbonate buffer, but did inhibit the response to 40 mM KCl. Cooling increased the tensions of the phasic responses to both concentrations of Carb in Ca(++)-depleted, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid-containing buffer, whereas the rate constant of decay of the phasic response (kdecay) was decreased only at 0.3 microM Carb. Nifedipine inhibited the tension and increased the kdecay of the phasic response to 10 microM Carb at both 37 and 25 degrees C. The phasic response to 0.3 microM Carb was essentially completely inhibited by nifedipine. The tension of the tonic response to Carb was unaffected by cooling and was only inhibited by nifedipine at 0.3 microM Carb at 37 degrees C. Both cooling and nifedipine, at 37 degrees C, decreased the rate constant of onset of the tonic response (kon) to Carb. The predominant effect of cooling to augment the phasic component of the contractile response to Carb, whereas it does not provide the mechanism to explain the enhanced bronchoconstrictor response of airways to cold, does suggest that Ca++ mobilization is altered by cold and that this may contribute to the enhanced bronchoconstrictor response.(ABSTRACT TRUNCATED AT 250 WORDS)     

哌仑西平抑制豚鼠形觉剥夺性近视的视网膜机制

目的观察哌仑西平对豚鼠形觉剥夺性近视的抑制效果,探讨其可能的作用机制。方法 1周龄豚鼠60只随机分为4组,每组15只,分别为正常对照组(Ⅰ组)、单纯遮盖组(Ⅱ组)、哌仑西平组(Ⅲ组)与氯化钠组(Ⅳ组);各组右眼为观察眼,左眼为对照眼。6周后检测4组豚鼠双眼屈光度、眼轴长度,免疫组织化学法及Western blot检测视网膜多巴胺转运蛋白(dopamine transporter,DAT)的表达水平,并进行统计分析。结果Ⅱ,Ⅳ组观察眼相对屈光度及眼轴长度变化与Ⅰ组比较差异有统计学意义(P<0.05),Ⅲ组与Ⅰ组比较差异无统计学意义(P>0.05);视网膜DAT阳性细胞数和DAT蛋白表达Ⅱ,Ⅳ组明显低于Ⅰ,Ⅲ组(P<0.05),Ⅰ组与Ⅲ组,Ⅱ组与Ⅳ组比较差异均无统计学意义(P>0.05)。结论哌仑西平能抑制豚鼠形觉剥夺性近视的发展,阻止近视视网膜DAT表达水平下降,推测哌仑西平可能通过影响视网膜多巴胺系统而抑制近视的发展。     

Antigen-induced enhancement of noncholinergic contractile responses to vagus nerve and electrical field stimulation in guinea pig isolated trachea.

Nonadrenergic, noncholinergic contractions were elicited by electrical field stimulation (EFS) (2 Hz, 1 msec, 12 V for 15 sec) of the distal aspect of guinea pig trachea pretreated with atropine (1 microM), propranolol (1 microM) and indomethacin (3 microM). The contractions were abolished by pretreatment with the sensory C-fiber toxin capsaicin or by a combination of the neurokinin (NK)1 receptor antagonist, CP 96,345 (0.1 microM), and the NK2 receptor antagonist, MEN 10376 (3 microM), and were markedly attenuated by tetrodotoxin. In animals actively sensitized to ovalbumin, the addition of threshold concentrations of antigen markedly increased the noncholinergic contractile responses to EFS (approximately 3- to 6-fold). This potentiation was long lasting, persisting virtually unchanged for 60 min, whereas the antigen-induced contractions were shorter lived, usually lasting less than 30 min. The ovalbumin-induced potentiation of the neuronal response was not observed in tissues pretreated with capsaicin or treated with tetrodotoxin. This antigen-induced potentiation of capsaicin-sensitive, EFS-induced contractions was not mimicked by serotonin or prostaglandin D2. However, it was mimicked by histamine. Moreover, the histamine H1 receptor antagonist pyrilamine (0.3 microM) reversed the potentiation elicited by ovalbumin. The effect of ovalbumin challenge was also examined on the distal trachea with the right vagus nerve intact. Noncholinergic contractions to EFS and vagus nerve stimulation were enhanced equally by threshold concentrations of antigen. The results support the hypothesis that antigen challenge releases histamine which acts via H1 receptors to enhance noncholinergic contractions due to the release of tachykinins from capsaicin-sensitive fibers in the guinea pig trachea.     

Effect of different ozone concentrations on the neurogenic contraction and relaxation of guinea pig airways

Summary— Prejunctional and postjunctional effects of several ozone (O₃) concentrations, including those found in highly polluted cities, were evaluated in guinea pig airways. Animals bred in O₃-free conditions were exposed to air or O₃ (0.3, 0.6 or 1.2 ppm) during 4 h, and studied 16–18 h later. Tracheal and bronchial rings were studied in organ baths. Electrical field stimulation (EFS) (100 V, 2 ms, 10 s) was given at increasing frequencies (0.25–16 Hz). Some tissues received atropine (2 μM) and/or propranolol (10 μM). Concentration-response curves to carbachol, isoproterenol, nitroprusside, and substance P were constructed. In tracheas, almost all O₃ concentrations decreased the relaxation at low EFS frequencies, but had no effect on the propranolol-resistant (i-NANC) relaxation, suggesting that only adrenergic relaxation was affected. This was a prejunctional effect, since O₃ did not modify the responses to isoproterenol. Relaxation induced by a nitric oxide (NO) donor, nitroprusside, was not affected by O₃, which agrees with the lack of O₃-effect on i-NANC system. O₃ did not modify the EFS-induced e-NANC contraction in atropine-treated bronchi, nor the contraction caused by exogenous substance P. By contrast, in bronchi without atropine, 1.2 ppm O₃ increased the e-NANC contraction induced by the highest EFS (16 Hz). O₃ increased the maximum responses to carbachol in tracheas (1.2 ppm) and bronchi (0.6 and 1.2 ppm). In conclusion, we found that: a) O₃ decreased adrenergic relaxation in guinea pig tracheas at low EFS frequencies through a prejunctional alteration; b) O₃ did not modify the i-NANC relaxation in tracheas, at least the NO-mediated; c) O₃ added a cholinergic component to the bronchial slow-phase (e-NANC) contraction evoked by EFS; and d) O₃ enhanced the cholinergic responses in trachea and bronchi by a postjunctional mechanism.     

Influence of electrical field stimulation on antigen-induced contraction and mediator release in the guinea pig isolated superfused trachea and bronchus

These studies examined the ability of electrical field stimulation (EFS) to influence antigen-induced responses in the guinea pig isolated trachea and main-stem bronchi. Airways isolated from guinea pigs actively sensitized to ovalbumin were superfused and stimulated transmurally with square pulses of 1 msec duration at a frequency of 16 pulses per sec. In the trachea, EFS caused an atropine-sensitive contraction followed by a maintained relaxation. The relaxation consisted of adrenergic and nonadrenergic components. In the bronchus, EFS caused a maintained contraction. This contraction was due to a combination of cholinergic (atropine-sensitive) and noncholinergic (capsaicin-sensitive) mechanisms. Histamine could not be detected in superfusate samples during electrical stimulation alone of either the trachea or bronchus. EFS significantly inhibited ovalbumin-induced tracheal contractions by about 30% without altering ovalbumin-induced histamine or immunoreactive peptido-leukotriene release from the tissues. EFS had a similar inhibitory effect on the contraction induced by application of exogenous histamine (10(-5) M). The electrical stimulus-induced inhibition of the antigen-induced contraction was abolished by tetrodotoxin and propranolol and reduced by a combination of atropine, propranolol and phentolamine. Norepinephrine (5 x 10(-6) M) inhibited ovalbumin-induced histamine release by about 30% without altering the contraction. Carbamylcholine had no effect on ovalbumin-induced histamine release. In the guinea pig bronchus, EFS stimulation had no effect on either histamine release or contraction induced by ovalbumin. These results demonstrate that in the guinea pig trachea nerve stimulation can significantly antagonize antigen-induced contractions and suggest that this is due to a functional antagonism by adrenergic and nonadrenergic relaxant neurotransmitters at the level of the airway smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)