Responses Of Tracheal Smooth Muscle Research Articles

Tracheal smooth muscle responses to upper airway pressure in conscious dogs

We studied the influence of changes in pressure applied to the isolated upper airway of four conscious dogs on tracheal smooth muscle tone and breathing pattern. The dogs were prepared with a permanent side-hole tracheal stoma and were trained to sleep with a snout mask hermetically sealed in place while breathing through a cuffed endotracheal tube inserted distally into the tracheal stoma. Changes in tracheal smooth muscle tone were continuously monitored by measuring the pressure in the water-filled cuff that distended the tracheal airway while pressure changes were introduced in the upper airway independently of breathing. Increases or decreases of upper airway pressure (+/- 10 cmH2O) had little effect on tracheal airway smooth muscle tone. In contrast, an oscillating pressure wave at 30 Hz and +/- 3 cmH2O amplitude (or -3 to -7 cmH2O amplitude) caused a marked increase in tracheal airway smooth muscle tone. An elevated tracheal airway tone could be maintained over many minutes when the oscillating pressure stimulus was pulsed so that there was a cycle of 0.5 s on, 0.5 s off. This stimulus did not change the functional residual capacity but resulted in coughing, swallowing, or sighing in 54% of the tests. In the remaining tests, the pressure stimulus produced a rapid, shallow, and erratic breathing pattern. The tracheal airway constrictor response (but not the ventilatory response) was completely abolished by intravenous atropine. We suggest that upper airway vibration is a potentially powerful mechanism of reflex airway smooth muscle constriction.

Effects of Lipopolysaccharide from <i>Pseudomonas aeruginosa</i> on Airway Smooth Muscle Functions in Guinea Pigs

To elucidate the mechanisms of airway hyperreactivity induced by lipopolysaccharide (LPS), we studied isolated tracheal segments from guinea pigs under isometric conditions in vitro. Guinea pigs were injected intraperitoneally with endotoxin (1 mg/kg; LPS from Pseudomonas aeruginosa, serotype 10) for 4 days, and animals treated with sterile nonpyrogenic saline served as controls. Histological examination of trachea revealed moderate structural damage of epithelial layer in the LPS-treated group. Treatment with LPS potentiated the contractile responses of tracheal smooth muscle to acetylcholine, causing a leftward displacement of dose-response curves so that the EC50 values decreased from 1.1 +/- 3.7 x 10(-5) to 4.4 +/- 3.7 x 10(-7) M (mean +/- SE, p less than 0.01). Likewise, LPS shifted the dose-response curves for histamine and substance P to lower concentrations by approximately 0.5-1.0 log U. Each of these potentiations was not affected by pretreatment of tissues with indomethacin or propranolol. Addition of isoproterenol to tracheal segments precontracted with acetylcholine caused concentration-dependent relaxation, an effect that was significantly greater in controls than in the LPS-treated group. These results suggest that airway hyperreactivity induced by LPS in guinea pigs may be attributed to a decreased ability of respiratory epithelial cells to generate a relaxing factor.

Influence of respiratory drive on airway responses to excitation of lung C-fibers.

To determine whether the responses of tracheal smooth muscle and the nasal vasculature to stimulation of lung C-fiber receptors depend on the level of respiratory drive, the effects of right atrial injection of capsaicin and phenyldiguanide were studied in chloralose-anesthetized, paralyzed, artificially ventilated cats. Studies were performed while the animals were hyperventilated to apnea and, in addition, when breathing was stimulated by inhalation of 7% CO2 or by N-methyl-D-aspartic acid (NMDA) applied to the ventral surface of the medulla. When the cats were hyperventilated to apnea with O2, injection of capsaicin into the right atrium increased tracheal tone and slightly raised nasal resistance. However, when the animals were ventilated with 7% CO2 in O2 or respiratory activity was stimulated by the application of NMDA, administration of capsaicin eliminated spontaneous phrenic nerve activity and caused an abrupt decrease in tracheal tone but still increased nasal resistance. Similar responses were also obtained with right atrial injection of phenyldiguanide. These results showed for the first time that in the cat the direction of the reflex effects on tracheal tone but not nasal resistance depends on the preexisting level of respiratory drive and on cholinergic activity to airway smooth muscle.

Effect of Nedocromil Sodium on Antigen-Induced Airway Responses in Allergic Sheep

We studied the effects of nedocromil sodium and sodium cromoglycate on early and late bronchial responses, the airway inflammation associated with the late response to inhaled Ascaris suum antigen in allergic sheep in vivo, and the antigen-induced contractile responses of sheep tracheal smooth muscle in vitro. In addition, we examined the effect of nedocromil sodium on the development of antigen-induced airway hyper-responsiveness in this model. Pretreatment with either nedocromil sodium or sodium cromoglycate was effective in blocking antigen-induced early and late responses in allergic sheep. Both drugs also prevented the influx of eosinophils into the airways as assessed by bronchoalveolar lavage, observed during the late response in this model. No difference in drug potency was observed in vivo, but in vitro nedocromil sodium was 10-fold more potent than sodium cromoglycate against antigen-induced contractions of sheep tracheal smooth muscle. Nedocromil sodium was effective in blocking antigen-induced late responses and the subsequent development of airway hyper-responsiveness irrespective of whether the drug was given before antigen challenge or after the immediate response to antigen but before the late response. These findings indicate that nedocromil sodium is effective in the sheep model of asthma and therefore may be beneficial in the treatment of reversible obstructive airway disease in man.

Effects of neuropeptides and capsaicin on the canine tracheal vasculature in vivo.

1. The nonadrenergic, noncholinergic nervous system may control the airway vasculature via various neuropeptides. We have perfused the cranial tracheal arteries of the anaesthetized dog and investigated the effects of neuropeptides and capsaicin (which is supposed to release neuropeptides from sensory nerve endings) on the tracheal vasculature by injecting them locally into the perfusion system. 2. Neurokinin A (NKA, 0.02-20 pmol), calcitonin gene-related peptide (CGRP, 2-200 pmol) and peptide histidine isoleucine (PHI, 0.02-2 nmol) dose-dependently decreased tracheal vascular resistance (Rtv). NKA was 10 and 100 times more potent than CGRP and PHI, respectively. The duration of the response to CGRP was greatly prolonged with larger doses. Galanin (0.2-2 nmol) had no appreciable effect on Rtv. 3. Neuropeptide Y (NPY 0.02-2 nmol) and bombesin (0.02-10 nmol) dose-dependently increased Rtv. However, the dose-response curve for bombesin was bell-shaped suggesting the development of tachyphylaxis with larger doses. In smaller doses, bombesin was twice as potent as NPY. The duration of the response to NPY was prolonged with larger doses. 4. With the exception of PHI no neuropeptide altered tracheal smooth muscle tone; PHI (1 and 2 nmol) caused small dilatations of the trachea. 5. The effects of capsaicin (2-100 nmol) were complex. Usually, the vascular response had two dose-dependent phases: a rapid vasoconstriction followed by a small, longer-lasting vasodilatation. The tracheal smooth muscle response was usually biphasic, a contraction followed by a relaxation. 6. According to previous and present data, the order of potency of the neuropeptides on the canine tracheal vasculature is for the vasodilators : NKA > vasoactive intestinal peptide (VIP) > CGRP > substance P > PHI, and for the vasoconstrictors: bombesin > NPY. The longer-acting neuropeptides (VIP, CGRP and NPY) may be more important than the shorter-acting neuropeptides (substance P, NKA, PHI and bombesin) as regulators of the airway wall blood flow.

Contractile responses of tracheal smooth muscle in organophosphate-treated swine: 1. Agonist changes.

1. Male weanling swine were injected daily for up to 14 days with the organophosphate cholinesterase inhibitors, diisopropylfluorophosphate (DFP) or sarin. The clinical signs of poisoning disappeared or were attenuated by 7 days after starting the DFP treatment, indicating the development of tolerance to DFP toxicity. 2. A significant decrease in acetylcholinesterase activity (85-98%) occurred over the course of this treatment followed by a decrease in the maximal density (Bmax) of [3H] quinuclidinyl benzilate ([3H]QNB) and [3H] N-methylscopolamine ([3H]-NMS) binding sites in isolated cells. The affinity of the muscarinic receptors (KD) for [3H]QNB and [3H]NMS binding, however, remained unaffected. 3. Dose-response curves for ACh-induced increase in isometric tension of tracheal smooth muscle (TSM) showed a leftward shift from control, 2 h after DFP injection. Twenty-four hours after the last DFP treatment, for animals receiving 1 or up to 14 daily injections of DFP, all the dose-response curves were shifted to the left to approximately the same ACh sensitivity when compared with that for control tissue. 4. In vitro treatment of the muscle with 10(-4) M DFP shifted the dose-response curves leftward, in both control and injected animals, and rendered the muscles from control, 1- and 3-day injected animals sensitive to ACh concentrations as low as 10(-10) M. Sensitivity to 10(-10) M ACh was eliminated by carefully cleaning the smooth muscle of adherent connective tissue containing nerves and ganglia and after subacute treatment of swine for 7 days with DFP. DFP-induced spontaneous contractions were also eliminated by careful cleaning. 5. Subacute DFP treatment caused a small leftward shift in the dose-response curve for bethanechol at 2 h and a rightward shift at 1,3 and 7 days, compared to controls. 6. Dose-response curves for K+ were shifted to the right after 1 and 3 days of DFP treatment, but shifted back towards the control after 7 days of treatment. The muscle cells were hyperpolarized by approximately 5 mV after 7 days of DFP or sarin injections. The membrane potential was slightly more sensitive to changes in K+ concentration after 7 days of sarin injection. 7. Subacute treatment of swine with organophosphates modifies the response of neural elements in swine TSM to ACh. Chronic cholinesterase inhibition causes a reduction in the sensitivity of the neural elements to ACh. The decrease in muscarinic receptor density which occurs with chronic cholinesterase inhibition is not sufficient to explain tolerance to organophosphates since TSM maintains an almost normal responsiveness to ACh.

Contractile responses of tracheal smooth muscle in organophosphate‐treated swine: 2. Effects of antagonists

1. Swine tracheal smooth muscles (TSM) developed spontaneous contractions following the acute administration of DFP in vivo and/or in vitro which could be blocked pharmacologically using atropine (2 x 10(-7) M), pirenzepine (3 x 10(-7) M), or hemicholinium 3 (HC3, 5 x 10(-6) M). 2. Treatment of TSM in vitro with DFP caused them to become responsive to ACh concentrations as low as 10(-10) M. 3. Atropine and pirenzepine (at 2 and 3 x 10(-7) M respectively) increased the EC50 concentrations for ACh approximately 300- and 8-fold respectively. The shifts caused by atropine and pirenzepine in the dose-response curves for ACh were not parallel after in vitro treatment of the muscle with DFP. By contrast, the shifts in the dose-response curves were parallel when muscles from swine injected for 7 days with DFP were used. 4. HC3 had no effect on the control dose-response curve for ACh, but steepened the dose-response curve after in vitro treatment of the muscle with DFP. The ACh dose-response curve obtained in the presence of HC3 and DFP was identical to that obtained using muscles from swine treated for 7 days with DFP. 5. McN-A-343, a partial agonist at muscarinic receptors, also induced contraction although the maximal tension induced was 56% of the maximal tension obtained using ACh. In vitro treatment of the muscle with DFP caused a leftward shift in the dose-response curve for McN-A-343. The muscles from animals treated for 7 days with DFP did not respond to McN-A-343 at doses up to 10(-3) M. 6. McN-A-343 competition for [3H]QNB binding suggested that the loss of the contractile response can be correlated with the loss of a high affinity site for McN-A-343 from the muscle. 7. We conclude that tolerance to DFP with subacute treatment results in part from the reduction in sensitivity of neural elements associated with swine tracheal smooth muscle to ACh. In addition the response to the partial agonist McN-A-343 is lost after subacute DFP treatment.

Is the epithelium-derived inhibitory factor in guinea-pig trachea a prostanoid?

To examine further the possible prostanoid involvement in the influence of the epithelium on guinea-pig tracheal smooth muscle responsiveness, we have analyzed the effects of LTD 4, methacholine and histamine on the level of airway smooth muscle tone and on the amounts of PGE 2α and PGI 2 (determined by radioimmunoassay) in the presence and absence of the epithelium. Removal of the epithelium increased the sensitivity of guinea-pig trachea to the contractile effects of LTD 4, methacholine and histamine. LTD 4 (3–100 nM), methacoline (0.1–10 μM) or histamine (0.3–30 μM) did not increase prostanoid release above control values in either the presence or absence of the epithelium. The unstimulated release of PGE 2 and PGF 2α but not PGI 2, was decreased in tissues lacking epithelium. Indomethacin (1 μM) reduced the baseline tone to a smaller extent in the absence of epithelium. In the presence but not the absence of the epithelium, indomethacin increased the sensitivity of preparations to the contractile effect of methacholine. The results support the postulate of an epithelium-derived inhibitory factor modulating guinea-pig tracheal smooth muscle responsiveness. The identity of this factor is not known but is not PGI 2 and is unlikely to be PGF 2α or PGE 2. However, the possibility remains that the basal release of PGE 2 and/or PGF 2α derived from the epithelium may markedly affect the responsiveness of guinea-pig tracheal smooth muscle. Furthermore, the epithelium is a significant source of PGE 2 and PGF 2α which may be involved in the maintenance of baseline tone.

Epithelium selectively controls hypersensitization of the response of smooth muscle to leukotriene D4 by endogenous prostanoid(s) in guinea-pig trachea.

The effect of epithelium removal on the sensitivity of smooth muscle to carbachol and leukotriene D4 (LTD4) was investigated in guinea-pig isolated tracheal preparations untreated and treated with a cyclooxygenase inhibitor, flurbiprofen (1 mumol/l). The pD2 value of carbachol was not changed by epithelium removal or by flurbiprofen-treatment, alone or in combination. On the other hand, the pD2 of LTD4 was higher in the tracheal strips without epithelium than in the intact preparations. In preparations devoid of epithelium, the pD2 value of LTD4 was decreased by treatment with flurbiprofen, suggesting that the sensitivity of the smooth muscle (namely, epithelium-free preparations) to LTD4 is enhanced by intramurally produced excitatory prostaglandin(s) [PG(s)]. However, in intact preparations with epithelium, no such sensitized response to LTD4 was observed. After flurbiprofen-treatment, in the continued presence of prostaglandin F2 alpha (PGF2 alpha, 200 nmol/l), the sensitivity to LTD4 was partially recovered in the epithelium-free preparations, but not in the intact ones. These results suggest that epithelium diminishes the sensitizing effect of intramural excitatory PG(s) on responsiveness of tracheal smooth muscle to LTD4, possible via a non-prostanoid substance(s).

Relationship between in vivo airway reactivity and in vitro responsiveness of tracheal smooth muscle in inbred rats.

We evaluated the in vivo and in vitro airway responses to cholinergic stimulation in two highly inbred strains of rats. Five Fisher and six Lewis rats inhaled aerosols of doubling concentrations of methacholine (MCh). Pulmonary resistance (RL) was measured before and after each MCh inhalation. The concentration of MCh required to double RL (EC200RL MCh) was calculated. Spirally cut tracheal strips were suspended in an organ bath and the isometric tension was recorded. Cumulative concentration-response curves to carbachol were obtained using concentrations ranging from 10(-9) to 10(-3) M in half-log increments. The maximum tension (Tmax) developed and the negative log of the molar concentration required to induce 50% of Tmax (pD2) were calculated. The geometric mean of ED200RL MCh for the Fisher group was significantly lower than that for the Lewis group (0.68 and 2.66 mg/ml, respectively; p less than 0.05). No significant difference was found for Tmax (0.67 +/- 0.11 vs. 0.50 +/- 0.11 g) and pD2 value (6.24 +/- 0.08 vs. 6.21 +/- 0.22 -log M), indicating a similar contraction of tracheal smooth muscle. We therefore conclude that (1) in vivo airway responsiveness is strain-related and genetically determined in the rat; (2) that there is no correlation between in vivo and in vitro airway response to cholinergic stimulation and (3) that intrinsic properties of airway smooth muscle do not account for the differences observed in airway responsiveness in vivo.

The Effect of Nedocromil Sodium and Cromolyn Sodium on Antigen-Induced Responses in Allergic Sheep in Vivo and in Vitro

We studied the effects of nedocromil sodium and cromolyn sodium on early and late bronchial responses to inhaled Ascaris suum antigen in allergic sheep in vivo, and the antigen-induced contractile responses of sheep tracheal smooth muscle in vitro. For the in vivo studies the sheep were pretreated with aerosols of placebo (buffered saline solution), 20 mg of nedocromil sodium, or 20 mg of cromolyn sodium (both dissolved in 3 ml of buffered saline solution) and then challenged with aerosol antigen. Specific pulmonary resistance (SRL) was measured before and after challenge to document the responses of the airways. In the trial with placebo, challenge with antigen resulted in significant early and late increases in SRL. Treatment with nedocromil sodium significantly reduced the early response to antigen and blocked the late response. Cromolyn sodium gave the same results; there were no statistical differences between the responses of the airways for the two dogs. In vitro nedocromil sodium at doses of 10(-6)M and 10(-5)M inhibited significantly the contractile responses of sheep tracheal smooth muscle to A suum. Cromolyn sodium only showed efficacy at 10(-5)M. These results suggest that nedocromil sodium may be potentially useful in the treatment of reversible allergic disease of the airways.

Local anaesthetics inhibit cholinergic and non-cholinergic neural and muscular contractions in avian tracheal smooth muscle.

The effects of five different local anaesthetics: lignocaine, prilocaine, etidocaine, mepivacaine, bupivacaine, on tone, contractility, and on cholinergic and non-cholinergic responses of chick tracheal smooth muscle were studied and compared in vitro. The cholinergic and non-cholinergic contractions of the tracheal smooth muscle were elicited by electrical field stimulation, at a maximal voltage with 0.2 Hz and 0.2 ms square pulse duration, in the presence of adrenergic blockers, guanethidine, propranolol, and other drugs, e.g. indomethacin. Atropine was used to reduce the cholinergic responses due to electrical field stimulation and to applied acetylcholine (ACh). Lignocaine, in low concentrations, reduced these responses and also those produced by electrical field stimulation in the presence of atropine. In high concentration (greater than 100 times clinical concentrations), lignocaine abolished all the responses and produced a sustained contracture in the muscle. Among the local anaesthetics studied, bupivacaine and lignocaine were found to be more effective than mepivacaine, prilocaine and etidocaine, in reducing the cholinergic contractions produced by electrical field stimulation and by exogenous ACh. It was suggested that lignocaine, and other local anaesthetic drugs, may have an anti-spasmic effect on the tracheal smooth muscle, in that they inhibited the contractions induced by electrical field stimulation and by depolarizing agents.

Epithelial modulation of tracheal smooth muscle response to antigenic stimulation.

The role of the epithelium has been studied in the contractile responses of rat trachea. The different modulations observed are discussed in respect to vagal components of the epithelial layer. Responses of rat trachea to immunologic stimulation are shown to be dependent on the presence of the epithelium, which prolongs the relaxation stage without affecting the contractions. This prolongation is abolished by neonatal capsaicin pretreatment, whereas substance P induces a significantly greater relaxation of serotonin-precontracted intact than deepithelialized trachea. Serotonin concentration-response curves are shifted to the right in intact preparations, which is partly reversed by neonatal capsaicin pretreatment, but a hyporeactivity of the tissue exists. A relaxing factor released by the epithelium is hypothesized, possibly dependent on substance P-ergic innervation. Muscarinic cholinergic innervation slightly modulates the contractions but not the relaxations in antigen-induced responses, independently on the presence of the epithelial layer. 4-Aminopyridine induces epithelium-dependent potentiations of contractions to antigen and to serotonin, which involves acetylcholine at one step of the reaction cascade. Epithelial-dependent contracting and relaxing factors are thus suggested in rat trachea.

Effects of extracellular calcium on canine tracheal smooth muscle.

Strips of canine tracheal smooth muscle were studied in vitro to determine the effects of changes in the extracellular calcium (Cao) concentration on tonic contractions induced by acetylcholine and 5-hydroxytryptamine. Strips were contracted with graded concentrations of the above agents in 2.4 mM Ca, after which CaCl2 was administered to achieve final concentrations of 5.0, 10.0, and 20.0 mM. Increases in Cao to 5 mM or above caused significant relaxation of muscles contracted with 5-hydroxytryptamine but did not significantly relax muscles contracted with acetylcholine. Increases in Cao also caused significant relaxation of muscles contracted with low concentrations of K+ (20 or 30 mM). However, in 60 or 120 mM K+, increases in Cao resulted predominantly in muscle contraction. Inhibition of the Na+-K+-ATPase by ouabain (10(-5) M) or K+ depletion reversed the effects of Cao from relaxation to contraction in tissues contracted with 5-hydroxytryptamine. Increases in Cao also caused contraction rather than relaxation in the presence of verapamil (10(-6) M). We conclude that calcium has both excitatory and inhibitory effects on the contractile responses of canine tracheal smooth muscle. The inhibitory effects of Ca2+ appear to be linked to the activity of the membrane Na+-K+-ATPase.

Endogenous modulation of alpha-adrenergic contraction in canine tracheal muscle.

We studied the effect of passive stretch on the contraction of canine tracheal smooth muscle (TSM) to alpha-adrenergic agonists and acetylcholine (ACh) in 211 epithelium-free TSM strips from 42 dogs in vitro. Passive stretch at a resting tension of 100 g/cm2 caused a time-dependent decrease in the contractile response to alpha-adrenergic agonists after beta-adrenergic blockade with propranolol. Initial contraction elicited by 10(-3) M phenylephrine (PE) and clonidine (CLO) decreased at 2 h by 31 and 100%, respectively. Decrease in alpha-adrenergic contractility did not result from tachyphylaxis; no contraction was elicited by PE or CLO given for the first time after 4-h passive stretch at 100 g/cm2. The TSM response to ACh was unchanged over the same time in the same strips. When TSM strips were incubated at zero resting tension for 6 h, some attenuation of the alpha-adrenergic contractile still occurred but was not substantial. Similarly, when strips were incubated with 10(-6) M indomethacin (INDO) or 10(-5) M mefenamic acid (MEF) at 100 g/cm2 resting tension, time-dependent attenuation of the response to PE and CLO was reduced for at least 6 h, and initial contraction elicited by PE was augmented. Response of TSM to ACh was not affected by prostaglandin synthetase inhibition with INDO. We conclude that passive stretch of canine TSM in vitro leads to decreased responsiveness to alpha-adrenergic stimulation that can be prevented with INDO or MEF. These data are consistent with the synthesis of an inhibitory eicosanoid in epithelium-free canine TSM that may be activated by mechanical deformation of the muscle.

K+-induced alterations in airway muscle responsiveness to electrical field stimulation.

We investigated possible pre- and postsynaptic effects of K+-induced depolarization on ferret tracheal smooth muscle (TSM) responsiveness to cholinergic stimulation. To assess electromechanical activity, cell membrane potential (Em) and tension (Tm) were simultaneously recorded in buffer containing 6, 12, 18, or 24 mM K+ before and after electrical field stimulation (EFS) or exogenous acetylcholine (ACh). In 6 mM K+, Em was -58.1 +/- 1.0 mV (mean +/- SE). In 12 mM K+, Em was depolarized to -52.3 +/- 0.9 mV, basal Tm did not change, and both excitatory junctional potentials and contractile responses to EFS at short stimulus duration were larger than in 6 mM K+. No such potentiation occurred at a higher K+, although resting Em and Tm increased progressively above 12 mM K+. The sensitivity of ferret TSM to exogenous ACh appeared unaffected by K+. To determine whether the hyperresponsiveness in 12 mM K+ was due, in part, to augmented ACh release from intramural airway nerves, experiments were done using TSM preparations incubated with [3H]choline to measure [3H]ACh release at rest and during EFS. Although resting [3H]ACh release increased progressively in higher K+, release evoked by EFS was maximal in 12 mM K+ and declined in higher concentrations. We conclude that small elevations in the extracellular K+ concentration augment responsiveness of the airways, by increasing the release of ACh both at rest and during EFS from intramural cholinergic nerve terminals. Larger increases in K+ appear to be inhibitory, possibly due to voltage-dependent effects that occur both pre- and postsynaptically.

Increased in vitro airway responsiveness in sheep following repeated exposure to antigen in vivo.

We have studied the effect of repeated in vivo antigen exposure on in vitro airway responsiveness in sensitized sheep. Fourteen sheep underwent five biweekly exposures to aerosolized Ascaris suum antigen or saline. Following this exposure regimen, the animals were killed and tracheal smooth muscle and lung parenchymal strips were prepared for in vitro studies of isometric contraction in response to histamine, methacholine, prostaglandin F2 alpha, and a thromboxane A2 analogue. No alteration in tracheal smooth muscle responsiveness was observed between saline- and antigen-exposed tissue. In contrast, by use of lung parenchymal strips as an index of peripheral airway responsiveness, significant increases in responsiveness to histamine and a thromboxane A2 analogue (10(-6) and 10(-5) M) were observed in antigen-exposed tissue compared with saline controls. These results demonstrate that repeated antigen exposure in vivo selectively increase the responsiveness of peripheral lung smooth muscle to certain chemical mediators of anaphylaxis.

Endogenous prostaglandins modulate histamine-induced contraction in canine tracheal smooth muscle.

We studied the role of endogenous prostaglandins in modulating the histamine response of canine tracheal smooth muscle (TSM) in vitro. Indomethacin (INDO) (10(-7) - 10(-5) M), a cyclooxygenase and prostaglandin synthesis inhibitor, significantly increased maximum histamine-induced tension (Tmax) and decreased the concentration of histamine required to produce 50% of Tmax (EC50). Acetylsalicylic acid (10(-5) -5 X 10(-4) M), another less potent cyclooxygenase inhibitor, also decreased EC50. Neither the lipoxygenase inhibitor nordihydroguaiaretic acid nor the leukotriene antagonist FPL 55712 had any effect on histamine-induced tension in INDO-pretreated TSM. INDO reduced the standard deviation of EC50 from 0.47 in control TSM (n = 51) to 0.26 in INDO-pretreated TSM (n = 31) (P less than 0.02). High-pressure liquid chromatography established prostacyclin (PGI2), through its degradation product 6-oxo-PGF1 alpha, as the predominant prostaglandin produced by canine TSM. Exogenous PGI2 caused a concentration-dependent relaxation of histamine-contracted TSM. In the tissue bath, spontaneous efflux of 6-oxo-PGF1 alpha from TSM, as measured by radioimmunoassay, averaged 4.7 ng . g muscle-1 . min-1 and increased to 10 ng/g muscle (n = 10, P less than 0.001) with administration of histamine. The isometric tension produced by histamine (10(-4) M) was inversely linearly correlated with the log concentration of endogenous 6-oxo-PGF1 alpha (r = 0.81, P less than 0.01). Our results are consistent with an important role for endogenous bronchodilating prostaglandins, probably prostacyclin, in determining both the histamine sensitivity of canine TSM in vitro and its variability among individual animals.

Mechanism of leukotriene-induced contraction of isolated guinea pig tracheal smooth muscle.

The mechanical response of guinea pig tracheal smooth muscle to leukotriene (LT) B4, C4, D4 and E4 was investigated, and the effects of several agents on LT-induced contraction were determined. Agents used in the present study were: verapamil, a Ca-channel blocker; dibutyryl cyclic-AMP (DBcAMP); aminophylline; N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7), a calmodulin antagonist; N-(6-aminohexyl)-1-naphthalene-sulfonamide hydrochloride (W-5), resembling W-7 in structure but without calmodulin antagonism. The results were as follows: 1) LTB4 had a contractile activity, dependent on the [Ca]o concentration; it was suppressed by a [Mg]o increase to 1.2 mM and over. Little effect was observed from other drugs. 2) Contractile activities of LTC4, D4 and E4 were dose-dependent, depending upon [Ca]o as well as LTB4. 3) Verapamil (5×10−6−10−3 M), DBcAMP (3×10−6−3×10−3 M) and aminophylline (3×10−8−3×10−3 M) suppressed LTs (C4, D4, and E4, 10−8 M)-induced contraction dose-dependently. However, W-7 and W-5 did not suppress LT-induced contraction. These results suggest that the LTC4-, D4-and E4-induced responses could be explained by the effect of LTC4, D4 and E4 on increasing Ca influx through the plasma membrane.

Static contraction of hindlimb muscles in cats reflexly relaxes tracheal smooth muscle

Static contraction of skeletal muscle is associated with increased ventilation. Although chemical stimulation of afferents from skeletal muscle causes relaxation of tracheal smooth muscle, it is not known if skeletal muscle contraction also causes tracheal relaxation. Therefore, in 10 chloralose-anesthetized cats, I examined the hemodynamic and tracheal smooth muscle responses to hindlimb skeletal muscle contraction induced by stimulating the L7 and S1 ventral roots. Isometric tension was measured in the transverse cervical trachea. During contraction average gastrocnemius tension increased from 0.7 +/- 0.1 to 4.9 +/- 0.6 kg, blood pressure and heart rate increased from 100 +/- 8 to 128 +/- 9 mmHg and from 192 +/- 11 to 202 +/- 13 beats/min, respectively, whereas tracheal tension decreased from 19.7 +/- 0.4 to 17.5 +/- 0.7 g (all P less than 0.02). There were significant (P less than 0.01) linear correlations between change in tracheal tension and maximal developed tension (r = -0.65), tension time (r = -0.68), and average developed tension (r = -0.76). Transection of the L7 and S1 dorsal roots in six cats reduced the tracheal relaxation associated with muscle contraction (pre: 19.9 +/- 0.3 to 17.5 +/- 0.3 g vs. post: 20.3 +/- 0.4 to 20.3 +/- 0.6 g) while average developed gastrocnemius muscle tension was not altered (pre: 1.1 +/- 0.1 to 6.4 +/- 1.1 kg vs. post: 1.2 +/- 0.2 to 6.8 +/- 1.2 kg). Thus static contraction of hindlimb muscles in cats reflexly lowers tracheal tension. This response is related to muscle mass and total tension generated by the contracting skeletal muscle.