Guinea Pig Tracheal Strips Research Articles

Mineral Dust Exposure and Free Radical-Mediated Lung Damage

Chronic exposure to several types of mineral dust particles induces an inflammatory reaction in the lung. Dust particles activate alveolar macrophages and prime leukocytes (neutrophils, eosinophils, and basophils), leading to an enhanced release of reactive oxygen species. Sometimes mineral dust particles also contain radicals. Reactive oxygen species (superoxide anion radical, hydrogen peroxide, hydroxyl radical, and singlet oxygen) may lead to tissue damage. These are able to break DNA strands, to destroy proteins, and to induce the process of lipid peroxidation. The effects of oxygen radicals on the beta-adrenergic and muscarinic receptor response of the guinea pig and rat tracheal strip are described. The beta-adrenergic receptor response appeared to be more susceptible to oxidative stress than the muscarinic receptor response. This may lead to an autonomic imbalance on exposure to oxygen radicals. The lipid peroxidation product 4-hydroxy-2,3-trans-nonenal diminished the beta-adrenergic responsiveness in guinea pig tracheal preparations. Histologic examinations indicated that at low concentrations of cumene hydroperoxide (10(-4) M) the epithelial layer of rat trachea was already destroyed, whereas no effect on the muscarinic response was found. Oxygen radical-mediated damage in lung tissue may lead to lung emphysema, hyperresponsiveness, and hypersensitivity. Pharmacotherapeutic interventions that prevent initiation or propagation of these free radical reactions may have a beneficial effect in mineral dust-associated lung disease.

Quinones. 4. Novel eicosanoid antagonists: synthesis and pharmacological evaluation.

A new series of omega-phenyl-omega-quinonylalkanoic acids and related compounds was synthesized. The compounds were tested for their inhibitory effects on U-44069-induced contraction of the rabbit aorta. (+/- )-7-(3,5,6-Trimethyl-1,4-benzoquinon-2-yl)-7-phenylheptanoic acid (4d) (AA-2414) with pA2 value of 8.28 was one of the most potent compounds. Compound 4d inhibited U-46619-induced contraction of the guinea pig lung (pA2 = 8.29) and U-44069-induced aggregation of the guinea pig platelet (IC50 = 3.5 x 10(-7) M). Compound 4d displaced the binding of [3H]U-46619 to guinea pig platelets (IC50 = 7.4 x 10(-9) M). Compound 4d also showed very potent inhibitory effects with an MED of 0.3 mg/kg (po) on U-46619-, LTD4-, PAF-, or IgG1-induced bronchoconstriction in guinea pigs. The enantiomers of 4d were prepared. The R-(+) isomer 8a was active in both in vitro and in vivo tests, but the S-(-) isomer 8b was much less active. We concluded that the antiasthmatic effects of 4d were based mainly on the TXA2 receptor antagonistic action. In addition, compound 4d showed potent inhibitory effects on PGD2-, PGF2 alpha-, and 11-epi-PGF2 alpha-induced contraction of the guinea pig tracheal strips. The diverse inhibitory effects might be expressed in terms of eicosanoid-antagonistic activity.

A novel anti-asthmatic quinone derivative, AA-2414 with a potent antagonistic activity against a variety of spasmogenic prostanoids

The anti-asthmatic activity of AA-2414 [(±)-7-(3,5,6-trimethyl-1,4-benzoquinon-2-yl-7-phenylheptanoic acid)] has been studied in vivo and in vitro. Experimental allergic asthma was inhibited by orally administered AA-2414 in a dose-dependent manner. AA-2414, 0.08∼1.25 mg/kg (p.o.), inhibited the bronchoconstriction in guinea pigs induced by a prostaglandin endoperoxide analogue (U-46619), leukotriene D 4 (LTD 4), and platelet activitating factor (PAF) with a long duration of action. The compound did not inhibit histamine-induced bronchoconstriction. AA-2414 reduced the induction of pulmonary inflation caused by LTD 4 aerosol inhalation. AA-2414 competitively inhibited the contractile response to U-46619 in guinea pig tracheal and parenchymal strips and dog saphenous vein strips with pA2 values of 7.69, 8.29 and 6.79, respectively. Furthermore, the contractile responses of guinea pig tracheal strip to PGD 2, 9 a, 11ß-PGF 2 and PGF 2 a were inhibited with pA2 values of 7.20, 7.79 and 5.71, respectively. These results suggest that AA-2414, a quinone derivative, is a novel, potent and orally active antagonist of a variety of spasmogenic prostanoids.

The classification of prostaglandin DP‐receptors in platelets and vasculature using BW A868C, a novel, selective and potent competitive antagonist

1. BW A868C, a novel compound, behaved as a simple competitive antagonist in a human washed platelet aggregation assay. Anti-aggregatory concentration-effect curves to BW 245C were displaced in a parallel manner. The shifts accorded with a Schild plot slope of unity and a pKB of 9.26. 2. Inhibition of platelet aggregation by prostaglandin D2 (PGD2) was antagonized with a similar potency, as were the relaxation effects of BW 245C and PGD2 in the rabbit jugular vein. BW A868C can, therefore, be classified as a DP-receptor antagonist. 3. Actions of BW A868C at other prostaglandin receptors (IP, EP1, EP2, TP and FP) were excluded at concentrations up to 1,000 times higher than the DP-receptor affinity. 4. Analyses of BW 245C- and PGD2-mediated effects were complicated by additional agonist receptor interactions which were revealed by BW A868C. In rabbit jugular vein a resistant phase of agonism was detectable, indicating that both agonists exerted effects through another receptor (possibly EP2). Also, PGD2, in addition to its anti-aggregatory effect on platelets, demonstrated a pro-aggregatory action in the presence of BW A868C. 5. The contractile effects of PGD2 in guinea-pig tracheal strips were resistant to 10 microM BW A868C indicating that they were not mediated through DP-receptors. 6. To our knowledge this is the first account of a well-classified competitive antagonist at the DP-receptor. Its potency and selectivity make it an important new tool in prostanoid receptor classification and identification.

Contraction of guinea pig trachea by epidermal growth factor--urogastrone.

To evaluate further the action of epidermal growth factor - urogastrone (EGF-URO) in smooth muscle systems, we examined the effect of the peptide on guinea pig tracheal strips. The cumulative addition of EGF-URO to the organ bath resulted in a concentration-dependent tonic contraction without tachyphylaxis. The half-maximal contraction was obtained at 13 +/- 3 ng/mL EGF-URO (2 nM). The maximum contraction at 100 ng/mL approached 60% of that induced by 1 microM histamine. No significant difference in the EGF-URO-induced contraction was observed in the presence or absence of a functional epithelium. Preincubation with 1 microM indomethacin for 20 min abolished the action of EGF-URO. The contractile effect of EGF-URO was not affected by yohimbine, propranolol, atropine, tetrodotoxin, and esculetin. However, mepacrine caused inhibition by 37 +/- 7% (mean +/- SEM for n = 3). Verapamil (10 microM) inhibited the EGF-induced response by 62 +/- 5% (mean +/- SEM for n = 4); the response was also absent in Ca-free (1 mM EGTA) buffer. However, the response was restored after the readdition of calcium. Our results suggest that EGF-URO can modulate tracheal smooth muscle contractility via a cyclooxygenase product and raise the possibility that EGF-URO might play a role in controlling pulmonary smooth muscle tone in vivo.

Structure-activity profile of a series of novel triazoloquinazoline adenosine antagonists.

During a search for benzodiazepine receptor modulators, a highly potent adenosine antagonist (CGS 15943) was discovered. The compound was defined as a resonance-stabilized hybrid of the canonical structures 9-chloro-2-(2-furyl)[1,2,4]triazolo[1,5-c]quinazolin-5-amine (2a) and 9-chloro-2-(2-furyl)-5,6-dihydro[1,2,4]triazolo[1,5-c]-quinazolin- 5-imine (2b). Spectroscopic evidence and chemical reactivity in polar media favor the amine form 2a as the major contributor of the two canonical structures. The synthesis of 2 and some of its analogues and the structure-activity relationships in four biological test systems are described. Replacement of the 9-chloro group by hydrogen, hydroxyl, or methoxyl gave compounds with comparable binding potency at the A1 and A2 receptors but much less activity as antagonists of 2-chloroadenosine in guinea pig tracheal strips. Alkylation of the 5-amino group caused, in general, a loss of binding activity, particularly at the A2 receptor, as well as complete loss of activity in the tracheal model. Modification of the 2-furyl group caused a pronounced loss of activity in all of the test systems.

Phenylephrine derivatives as leukotriene D4 antagonists.

Two series of phenylephrine derivatives were prepared and tested as inhibitors of leukotriene D4 (LTD4) induced and ovalbumin-induced bronchospasm in the guinea pig. The most potent compound of the urea series, (R)-N,N-diethyl-N-[2-hydroxy-2-[3-(2-quinolinylmethoxy)phenyl]ethyl]-N- methylurea (3, Wy-47,120), was orally active with ED50's of 56 mg/kg vs. LTD4 and 55 mg/kg vs. ovalbumin. When tested as an antagonist of LTD4-induced contraction of isolated guinea pig tracheal strips, 3 was a competitive inhibitor with a p kappa B value of 5.22. In the second series, (R)-3-methyl-5-[3-(2-quinolinylmethoxy)phenyl]-2-oxazolidinone (26, Wy-47,674) had oral ED50's of 36 mg/kg against LTD4 and 95 mg/kg against ovalbumin. Compound 26 selectively antagonized contractile responses of guinea pig trachea evoked by LTD4 (p kappa B = 6.09). In the cat coronary artery, 3 dilated the preparation and blocked the coronary constrictor effect of LTD4. Compound 3 (0.13 mg/kg, iv) also preserved myocardial integrity in rats 48 h after coronary artery ligation. When tested in the rat alcohol-induced gastric lesion model, 3 and 26 manifested a dose-dependent mucosal protection against ethanol.

Neurokinin A as a potent bronchoconstrictor.

Neurokinin A (NKA) and B (NKB) were more potent bronchoconstrictive agents than substance P (SP) in guinea pig tracheal strips. The content of NKA in guinea pig lung homogenate was 2.26 +/- 1.09 pmol/g wet lung, which was approximately half that of SP (4.46 +/- 1.33 pmol/g wet lung); NKB was not detected in the guinea pig lung homogenate (less than 0.01 pmol/g wet lung). Histologically, NKA-immunoreactive fibers were distributed in the bronchial smooth muscle layers. Pulmonary arteries and veins were also found to be innervated by NKA-immunoreactive nerves. In addition, a few fibers were observed in the trachea, bronchioles, and alveoli. These findings suggest that NKA may be one of the neurotransmitters of the noncholinergic bronchoconstrictive nerves.

Pharmacologic profile of chemically stable analogs of peptide leukotrienes

Peptide leukotrienes are potent constrictors of airway smooth muscle but lack chemical stability. Replacement of the natural triene backbone of leukotrienes with 9-(x-heptylphenyl)-7-nonenoic acid ( x = 2, 3, or 4) renders these analogs chemically stable and pharmacologically active. The para, meta and ortho substitutions of the heptyl (C 7H 15) moiety were combined with the different leukotriene peptide substitutions of glutathionyl, C-peptide of leukotriene C 4, cysteinylglycinyl, D-peptide of leukotriene D 4, and cysteinyl, E-peptide of leukotriene E 4 rendering nine active analogs. The pharmacology of these analogs was evaluated in isolated guinea-pig tracheal strips. The para-substituted C-peptide analog was the most potent; however, it was 100-fold less potent than leukotriene C 4. The contractile activities of the para- and meta-substituted C-peptide analogs were enhanced by L-serine borate (45 mM), indicating they were substrates for γ-glutamyl transpeptidase. FPL55712 (10 μM) failed to antagonize the substituted C-peptide analogs independent of the presence of L-serine borate. The contractile activities of the three substituted D-peptide analogs were enhanced by L-cysteine, indicating they are all substrates for aminopeptidase. The para-substituted D-peptide analog was the most potent D-peptide analog, but it was 10- and 1000-fold less active than the para-substituted C-peptide analog and leukotriene D 4, respectively. The para- and meta-substituted E-peptide analogs were approximately 1 000-fold less potent than leukotriene E 4, and like the substituted D-peptide analogs, they were antagonized by FPL55712. In contrast, the ortho-substituted E-peptide analog was devoid of intrinsic activity but antagonized leukotriene E 4-induced contractions. This investigation demonstrates that relatively potent, stable analogs which possess either agonist or antagonist activities can be developed. The pharmacologic profile of these analogs was qualitatively similar to that of the natural leukotrienes and lends further support for a distinct leukotriene C 4 receptor.

Pharmacological comparison of L-serine borate and glutathione as inhibitors of metabolism of LTC 4 to LTD 4 by the isolated guinea pig trachea

Cumulative dose-response curyes to leukotriene C 4 (LTC 4) and leukotriene D 4 (LTD) 4 were obtained on indomethacin (5 μM) treated isolated guinea pig tracheal spiral strips. LTC 4 curves, in the presence of either glutathione (GSH; 10 mM) or L-serine borate (SB; 45 mM), were not antagonized by FPL-55712 (3 μM), a selective LTD 4 receptor antagonist. LTC 4 curves on trachea treated with a lower concentration of GSH (1 mM), and LTD 4 curves were competitively antagonized by FPL-55712. LTC, curves on GSH (10 mM) treated trachea were 2 fold to the left of those on SB treated tissues. This effect of GSH was blocked by pretreatment with nordihydro-guiaretic acid (30 μM), an inhibitor of 5-lipoxygenase. GSH (10 μM) and SB (45 mM) are effective inhibitors of conversion of LTC 4 into functionally important levels of LTD 4 by the guinea pig trachea. In addition, GSH appeares to enhance LTC 4 responsiveness by increasing synthesis of a contractile 5-lipoxygenase product(s), possibly LTC 4. From the data it is suggested that for inhibition of LTC 4 metabolism, SB may be more usefull when examining responses to exogenously applied LTC 4, while GSH (10 mM) may be useful when examining responses to endogenously generated LTC 4.

The development of tone in the smooth muscle of guinea-pig isolated tracheal preparations may be influenced by prostanoids released from the adjacent airway cartilage

Guinea-pig tracheal strip preparations containing cartilage, placed under an applied load in vitro , develop tone spontaneously. The finding that spontaneous tone is reduced by indomethacin suggests that one or more prostanoids are involved in the development of spontaneous tone in this species. In this study we examined the effects of removing the cartilage component of the preparations on changes in tone induced by indomethacin and isoproterenol. In contrast to preparations containing cartilage, tissues devoid of cartilage, did not develop tone after the application of an initial 1 g resting load. Indomethacin (1 μM) reduced resting tone by 0.62 ± 0.14 g in cartilage-containing tissues but, in contrast, reduced tone by only 0.03 ± 0.01 g in tissues devoid of cartilage. Furthermore, relaxation responses (0.38 ± 0.05 g) to isoproterenol (1 μM) could be produced in cartilage-containing preparations but not in cartilage-free preparations. Radioimmunoassays indicated that the release of PGE 2, PGF 2α and 6-keto PGF 1α, the end-product of PGI 2 breakdown, was diminished in preparations lacking cartilage. Thus, in guinea-pig airway preparations cartilage is apparently a source of sufficient prostanoids to induce spontaneous tone

Effects of aerosol antigen challenge in vivo on responsiveness of guinea pig tracheal and parenchymal strips in vitro to contractile agonists.

Guinea pigs sensitized to produce IgG-like antibodies were challenged with aerosol antigen in vivo. The following day responses in vitro to histamine and carbachol of tracheal and lung parenchymal strips (LPS) from challenged animals and unchallenged controls were compared. Responses of LPS to both histamine and carbachol were increased in challenged animals but tracheal strips from challenged guinea pigs did not display increased sensitivity to histamine or carbachol compared with controls. Moreover, the sensitivity of tracheal strips to carbachol decreased in challenged animals. The increased sensitivity of LPS from challenged animals may be due to the release of chemical mediators and down regulation of postsynaptic muscarinic receptors may account for the decreased sensitivity of tracheal strips.

Antagonistic effect of KC-404, a new anti-asthmatic agent, on leukotriene D 4-induced contractile responses in isolated guinea pig smooth muscles

The inhibitory effects of KC-404, a novel clinically available anti-asthmatic drug, on leukotriene (LT) D 4-, LTC 4, histamine- and acetylcholine (Ach)-induced contractile responses in isolated guinea pig lung parenchymal, tracheal and ileal longitudinal strips were compared using an organ bath system. In lung parenchyma, KC-404 antagonized LTD 4 in a competitive fashion, whereas it antagonized histamine noncompetitively. The pA 2 value against LTD 4 was 7.39. KC-404 hardly antagonized LTC 4 and ACh. A ranked order of potency estimated from its minimum effective concentrations (MEC) was LTD 4 > histamine > LTC 4 > ACh. In trachea, KC-404 antagonized LTC 4 and LTD 4 in a competitive fashion, while it antagonized histamine noncompetitively. The pA 2 values against LTC 4 and LTD 4 were 5.99 and 6.51, respectively. KC-404 hardly antagonized ACh. A ranked order of the potency estimated from MEC was LTD 4 > LTC 4 > histamine > ACh. The pA 2 values of KC-404 against LTD 4 in lung parenchyma and trachea were little or not altered, while its inhibitory effect on histamine-induced contraction in trachea was markedly diminished by the pretreatment of tissues with indomethacin. In ileum, KC-404 noncompetitively antagonized all of the agonists used. A ranked order of the potency estimated from pD 2 values was LTD 4 ≒ LTC 4 > histamine > ACh. These results suggest that KC-404 is a selective antagonist of LTD 4 and that it might interact with LTD 4 receptor in airway smooth muscles but not in ileum. Another possibility that the drug might interact with LTD 4 specific excitation-contraction coupling mechanism was also discussed.

Synthesis and antiallergic activity of a novel series of 5-lipoxygenase inhibitors.

A series of novel substituted [[(phenoxymethyl)phenyl]amino]oxoalkanoic acid esters have been synthesized. These compounds were tested in vitro for their ability to inhibit the synthesis of 5-hydroxyeicosatetraenoic acid and leukotriene (LT) B4 from rat polymorphonuclear leukocytes (PMN) and in vivo as inhibitors ovalbumin- (OA) and LTD4-induced bronchospasm in the guinea pig. Compounds 5-12 and 25 had IC50's between 1 and 5.6 microM in the rat PMN 5-lipoxygenase assay. Compounds 1, 3, and 16 inhibited OA-induced bronchoconstriction (61%, 64%, and 57%, respectively), but only 1 showed activity against LTD4-induced bronchoconstriction. When tested against LTD4-induced contraction of isolated guinea pig tracheal spiral strips, 1 was a competitive inhibitor with a pKB of 4.94.

A note on responses of isolated guinea-pig tracheal strip preparation to electrical stimulation.

Authors observed the mechanical response of the tracheal muscle to electrical stimulation using only one transverse strip preparation of isolated guinea-pig trachea, 4-5 mm in width, which included only one tracheal muscle strip. The effects of various pharmacological agents on these responses were also investigated. A biphasic response which is a contractile response followed by a relaxing response usually appeared when the preparation was stimulated with rectangular pulses (50 volt, 0.5 msec) at 40 Hz for a period of 5 sec. A monophasic contractile response also appeared, only rarely but this response was shifted to the biphasic response as the resting tonus level of the preparation gradually increased in the course of the experiment. When the preparation was stimulated electrically at intervals of 15 min, the resting tonus level of the preparation gradually decreased and it subsequently reached a stable state. Then the amplitude of contractile response and depth of relaxing response in the biphasic response evoked by electrical stimulation of constant condition were, respectively, almost constant, whenever the preparation was stimulated at intervals of 15 min. The amplitude of monophasic contractile response which appeared only rarely was relatively constant to every trial of electrical stimulation throughout the experiment. The amplitude of contractile response and depth of relaxing response in the biphasic response were 283 +/- 65 mg (mean +/- SD, n = 10) and 293 +/- 93 mg (mean +/- SD, n = 10), respectively. The monophasic contractile response was abolished by atropine (5 X 10(-7) g/ml) or tetrodotoxin (2 X 10(-7) g/ml). The contractile response in the biphasic response was abolished by atropine (5 X 10(-7) g/ml). In the presence of atropine (5 X 10(-7) g/ml), therefore, only the relaxing response appeared. This relaxing response was respectively reduced by guanethidine (1 X 10(-5) g/ml-1 X 10(-6) g/ml) and propranolol (1 X 10(-5) g/ml-1 X 10(-6) g/ml), but complete inhibition was never seen. These findings suggest that the excitatory innervation is cholinergic and the inhibitory innervation is both adrenergic and non-adrenergic. In addition, from the results of this work it is clear that the preparation used by the authors are good enough to observe the electrical stimulation-induced response of the preparation.

EFFECT OF KETOTIFEN CN IN-VTTRO BRCNCHOCCNSTRICTION

Ketotifen has been used in the treatment of asthma for over six years, but its place in management remains controversial. We aimed to reappraise the efficacy of ketotifen at concentrations of 10−4 and 10−6M, on two in-vitro models of bronchoconstriction: actively sensitized guinea pig tracheal strips (G.P.T.), and passively sensitized human bronchial muscle strips (H.B.M.). Experiments were performed on matched pairs of tissues. An initial maximal acetyl choline induced response was obtained for each tissue, and all other contractions expressed as a percentage of this. Cumulative dose response curves [C.D.R.C] to histamine or acetylcholine were constructed, and repeated with or without ketotifen. Maximal antigen induced contractions were also compared. Results were analysed using paired t-tests. Contraction of G.P.T. by histamine and acetylcholine was inhibited by ketotifen, but antigen challenge was not affected. Contraction of H.B.M. by acetyl choline and antigen was inhibited by ketotifen. We were unable to obtain reproducible histamine C.D.R.C.'s for H.B.M. In both models the effect of ketotifen was dose related, with attenuation or loss of efficacy at 10−6M, a level close to that attained in clinical practice. These results support the concept of dose dependancy of clinical efficacy of ketotifen, and suggest that therapeutic trials of even higher doses may be warranted.

Bronchorelaxing Activity of Lithium In Vitro

The potential value of lithium as a bronchodilator has been evaluated by in vitro methods using guinea pig tracheal spirals and lung parenchymal strips. The use of twin spirals and strips prepared by splitting the tissues longitudinally into two equal halves has been used to minimize animal variations. The cumulative concentration–effect relationships of isoproterenol have been determined on these twin tissues contracted submaximally with histamine. The responses of the twin tissues did not significantly differ. The cumulative concentration–effect relationships of lithium on guinea pig tracheal spirals and lung parenchymal strips have been evaluated and compared with those of isoproterenol. Lithium showed a dose-dependent relaxation on both tissues. However, the potency of lithium to produce a relaxant effect was significantly lower than isoproterenol. The relaxing effect of lithium on parenchyma was significantly higher than that on the trachea. The lithium-induced inhibitory effect on the contractile responses of tracheal spirals and lung parenchymal strips to histamine before and after incubating the tissues with lithium for 15min has been determined. Lithium significantly reduced the contractile effect of histamine on both tissues. These findings suggest a potential clinical applicability of lithium for treating airway hyperresponsiveness.

Application of the operational model of agonism to establish conditions when functional antagonism may be used to estimate agonist dissociation constants.

The operational model of agonism (Black & Leff, 1983) has been used to analyse comparatively functional antagonism and irreversible antagonism as methods for estimating agonist dissociation constants (KAs). A general condition is established in terms of the model parameters which defines the type of experimental interventions at the receptor and the post-receptor level that allow valid KA estimation. It is shown that functional antagonism and other post-receptor interventions may produce changes in agonist-concentration effect curves which are qualitatively indistinguishable but quantitatively distinct, from those produced by irreversible antagonism. Experimental data obtained with the guinea-pig tracheal strip preparation are in keeping with the theoretical predictions and show how studies using functional antagonism may overestimate agonist affinity. In general, functional antagonism, unlike irreversible antagonism, is in principle an unreliable method for quantifying agonism.

Interaction of various leukotrienes in guinea pig tracheal and lung parenchymal strips

Interaction of various leukotrienes in guinea pig tracheal and lung parenchymal strips

Effects of Verapamil on Histamine and Carbachol-Induced Contraction of Pulmonary Tissues in Vitro

It has been hypothesized that calcium antagonists may be useful in the management of airway hyperreactivity. In these studies, we evaluated the effects of verapamil on guinea pig tracheal spirals and parenchymal lung strips in vitro. Preincubation of both tissues with verapamil caused concentration-dependent inhibition of contraction with significant effects noted at a 10 micromolar concentration. At this concentration of verapamil, approximately fivefold greater concentrations of either histamine or carbachol were required to produce contraction of tracheal spirals; and 21-fold greater concentrations of histamine and 630-fold greater concentrations of carbachol were required to contract parenchymal strips. We also assessed the ability of verapamil to reverse contraction. Significant reversal of both histamine- and carbachol induced contraction was observed with concentrations of 3 micromolar verapamil and contraction was nearly abolished with a 100 micromolar concentration. These data demonstrate that verapamil can both inhibit airway contraction and reverse contraction once it is present and further suggest that verapamil or other calcium antagonists may prove useful in the management of airway hyperreactivity.