Guinea-pig Lung Strip Research Articles

Differential relaxant responses of guinea-pig lung strips and bronchial rings to sodium nitroprusside: a mechanism independent of cGMP formation.

The biochemical mechanism subserving smooth muscle relaxant effects of sodium nitroprusside was examined on U46619, 9,11-dideoxy-9 alpha,11 alpha-methanoepoxy PGF2 alpha, precontracted guinea-pig lung strips and hilar bronchial rings. Lung strips were resistant to the relaxant action of sodium nitroprusside or sodium nitrite (NaNO2), whereas they markedly relaxed to 8-bromo-cyclic GMP (8-Br-cGMP), a membrane permeable analogue of cGMP. Precontracted bronchial rings completely relaxed to sodium nitroprusside, NaNO2, or 8-Br-cGMP in a concentration-dependent manner. Sodium nitroprusside (10 microM) substantially raised tissue cGMP level in lung strips. Conversely, sodium nitroprusside had no detectable effect on cGMP levels in bronchial rings. In the presence of 10 microM dipyridamole, an agent which preferentially inhibits cGMP-specific phosphodiesterase, cGMP levels in lung strips treated with sodium nitroprusside was significantly enhanced, but sodium nitroprusside demonstrated no relaxant effect on the preparations. However, dipyridamole potentiated sodium nitroprusside-induced precontracted bronchial ring relaxation without affecting the bronchial tissue cGMP level. In the presence of 10 microM LY83583 (6-anilino-5,8-quinoline-dione), a specific cGMP concentration-lowering agent, sodium nitroprusside-mediated elevation of cGMP level in lung strips was significantly reduced with no effect on the functional response. LY83583 demonstrated no inhibitory effect on either relaxation or cGMP level in bronchial rings treated with sodium nitroprusside. Our results suggest that precontracted smooth muscle in lung strips and in hilar bronchi respond distinctly to sodium nitroprusside. Furthermore, sodium nitroprusside mediates bronchial smooth muscle relaxation by mechanisms unrelated to cGMP.

The relation between effects of adenosine, theophylline and enprofylline on the contractility of sensitized guinea-pig lung strips

Contractile responses of lung parenchymal strips from ovalbumin-sensitized guinea-pigs to cumulative addition of antigen were significantly potentiated by 10 min pretreatment with adenosine 10 microM. This potentiation was unaffected by the adenosine uptake inhibitor, dipyridamole, 2 microM. Cumulative addition of adenosine 0.1-100 microM to parenchymal strips without antigen produced variable responses, unrelated to sensitization, some contracting, some relaxing. Theophylline 100 microM caused relaxation of parenchymal strips and significantly inhibited the antigen-induced contraction with a parallel shift of the log concentration-response line. It also inhibited the adenosine-induced potentiation of contraction. Enprofylline 100 microM caused a greater relaxation of the tissue than theophylline. While it inhibited the adenosine-induced potentiation of the response, enprofylline, in contrast to theophylline, failed to inhibit the antigen-induced contraction of guinea-pig parenchyma. At these concentrations, theophylline and enprofylline each inhibited the antigen-induced release of SRSA (leukotrienes C4, D4 and E4), and of histamine, from sensitized guinea-pig lung fragments.

Characterization of the muscarinic receptor subtype(s) mediating contraction of the guinea-pig lung strip and inhibition of acetylcholine release in the guinea-pig trachea with the selective muscarinic receptor antagonist tripitramine.

1. The muscarinic receptor subtypes mediating contraction of the guinea-pig lung strip and inhibition of the release of acetylcholine from cholinergic vagus nerve endings in the guinea-pig trachea in vitro have previously been characterized as M2-like, i.e. having antagonist affinity profiles that are qualitatively similar but quantitatively dissimilar compared to cardiac M2 receptors. The present study sought to establish definitely the identity of these receptor subtypes by using the selective muscarinic receptor antagonist, tripitramine. Guinea-pig atria and guinea-pig trachea (postjunctional contractile response) were included for reference. 2. It was found that tripitramine antagonized methacholine-induced contractions of the guinea-pig lung strip with pKB value of 8.76 +/- 0.05. Both the parallel shifts of the concentration-response curves and the slope of the Schild plot begin not significantly different from unity (when antagonist preincubation was for 2 h) indicated the involvement of a single population of receptors in the contractile response. From the pKB values obtained with tripitramine and a range of other selective muscarinic receptor antagonists (cf. Roffel et al., 1993), this single population of receptors can only be classified as M2-like. 3. Tripitramine antagonized methacholine-induced chronotropic and inotropic responses in guinea-pig right and left atria with apparent pKB values of 9.4-9.6. However, such values were only obtained when antagonist preincubation was relatively long and/or antagonist concentration relatively high (e.g with 1 h at 100 or 300 nM but 3 h at 30 nM). It thus appears that low concentrations of tripitramine do not readily equilibrate with M2 receptors in guinea-pig atria nor with M2-like receptors in the guinea-pig lung strip. 4. Tripitramine increased electrical field stimulation-induced cholinergic twitch contractions in guinea-pig trachea in concentrations of 0.3-100 nM, by blocking prejunctional muscarinic inhibitory autoreceptors; with higher concentrations, twitch contractions were progressively diminished, as a result of blocking postjunctional M3 receptors (apparent pKB value 6.07 +/- 0.15). The pEC20 value (-log concentration that increases twitch by 20% maximum) was 8.29 +/- 0.08, which would suggest that M4 receptors are involved in this response. 5. Oxotremorine-induced inhibition of the release of prelabelled [3H]-acetylcholine from guinea-pig trachea, under conditions where there is no auto-feedback, was blocked by tripitramine (2 h preincubation) with a pKB value of 8.56 +/- 0.06. The slope of the corresponding Schild plot was not significantly different from unity, which together with the parallel shifts of the concentration-response curves indicated the involvement of a single muscarinic receptor subtype. 6. Since the pKB value for tripitramine at prejunctional receptors in guinea-pig trachea is in between the affinities towards M2 and M4 receptors, correlation plots were constructed to compare the pKB values obtained with tripitramine and a range of other selective muscarinic receptor antagonists (cf. Kilbinger et al., 1995) to reported affinities at M1-M4 receptors. This showed rather similar distribution patterns of the data points around the line of equality in the case of M2 and M4 receptor subtypes. However, the correlation coefficient was markedly better for M2 (0.9667) than for M4 (0.5976). Since recent evidence suggests that M4 receptors are not expressed in cholinergic nerves from guinea-pig trachea, it is concluded that prejunctional muscarinic autoinhibitory receptors in this tissue exhibit an atypical M2 type character, with a pharmacological profile distinct from cardiac M2 receptors.

A new type of bradykinin B2 receptor antagonists: bradykinin analogs with N-alkyl amino acids at position 2

It is commonly assumed that bradykinin B2 receptor antagonists bind to a receptor site partially different from that for agonists. Thus, it is likely that there exists more than one key modification to convert bradykinin receptor agonists into antagonists. In this respect, [L-NMePhe2]-BK represents the basic structure of a new type of bradykinin B2 receptor antagonists without any replacement at position 7. This compound inhibits both in vitro bradykinin-induced contraction of the guinea pig lung strip and in vivo bradykinin-induced bronchoconstriction. Furthermore, this analog shows analgesic activity, blocks in a dose-dependent manner the bradykinin-induced Ca2+ release from macrophages and inhibits at a concentration of 10−13 M the bradykinin-induced cytokine release from mononuclear cells. Combinations with structural modifications previously performed for other B2 receptor antagonists rather reduce than enhance the potency.

Bombesin-induced contractions of guinea pig lung strips are modulated by endogenous nitric oxide.

We have investigated the effects of a nitric oxide (NO) biosynthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on the bombesin-evoked contraction of guinea pig parenchymal lung strips. The bombesin-induced contractions of lung strips were significantly increased after L-NAME (300 micro)) pre-treatment. The maximal response was increased (P < 0.01) by 37% after L-NAME treatment when compared with the control group. The pD2 value was not influenced by L-NAME pre-treatment. The enhancement of the bombesin-induced contraction caused by L-NAME was reversed by addition of an excess of the NO precursor L-arginine (600 microM) but not by the addition of its inactive enantiomer D-arginine (600 microM). Like L-NAME, methylene blue (1 microM), an agent that inhibits the soluble guanylyl cyclase activated by NO, significantly increased (P < 0.01) the maximal contraction induced by bombesin (183 +/- 16 mg) when compared with the control group (141 +/- 15 mg). When tested against other agonist-induced contractions, L-NAME did not change the responsiveness of parenchymal lung strips to bradykinin or carbachol but significantly increased lung contraction induced by histamine. NO synthesis inhibition resulted in a pronounced increase in the bombesin-induced contraction of guinea-pig lung strips. Our results suggest that bombesin contributes to NO synthesis and release which then acts to reduce the contraction of the lungstrip in response to bombesin.

New cyclic bradykinin antagonists containing disulfide and lactam bridges at the N-terminal sequence.

Continuing our studies of the bioactive conformation of bradykinin (BK) antagonists, we synthesized a first series of analogues with side-chain cyclization in the N-terminal sequence. Through this conformational constraint it should be possible to gain insight into their three-dimensional structure. The cycles were proposed on the basis of existing ideas and hypotheses about the receptor bound conformation of BK and its antagonists. The reported peptides contain D-Phe at position 7 or D-Tic-Oic (D-Tetrahydroisoquinoline-3 -carboxyl-octahydroindole-2-carboxylic acid) at positions 7 and 8, respectively, and a disulfide or lactam bridge between positions 0 and 6. Syntheses, including cyclization reactions, were carried out on PAM resin. The biological activity of the lead compound [DPhe7]-BK, the linear precursors and the cyclic peptides, as estimated on isolated rat uterus, guinea pig ileum and lung strips, are in the same range. The conformational properties of the new cyclic analogues were studied through energy minimization on a model compound. The results of the calculations support the existence of low-energy structures containing a beta-turn. Therefore, such a turn in the N-terminal segment of the molecule can be proposed as an important structural feature of the bioactive conformation of BK antagonists.

Tachykinin receptors mediating contraction of guinea pig lung strips

The aim of this study was to determine which tachykinin receptors mediate contraction in guinea pig lung parenchymal strips in vitro. Contraction caused by selective neurokinin-1 (NK-1), neurokinin-2 (NK-2), and neurokinin-3 (NK-3) receptor agonists and the natural agonists substance P (SP) and neurokinin A (NKA) was measured in the absence or presence of the NK-1 antagonist CP-96,345 and/or the NK-2 antagonist SR 48968. The NK-1 agonist [Sar 9, Met(O 2) 11]-substance P and the NK-2 agonist [Nle 10]-neurokinin A 4–10 caused similar concentration-dependent contractions that were inhibited by CP-96,345 and SR 48968, respectively. The NK-3 agonist [MePhe 7]-neurokinin B also caused contraction, albeit at 10-fold higher concentrations, and this contraction was unaffected by either the NK-1 or NK-2 antagonist or the combination of both antagonists. Either CP-96,345 or SR 48968 alone had little effect on NKA-mediated contraction but administration of both antagonists virtually eliminated force generation. SP-induced tension was partially inhibited by SR 48968 and unaffected by CP-96,345. A second NK-1 receptor antagonist CP-99,994 also had no effect on SP-mediated tension. Therefore, NK-1, NK-2, and NK-3 agonists can all cause contraction in guinea pig lung strips, NKA-induced tension is mediated by both NK-1 and NK-2 receptors, and SP-induced contraction is mediated in part by NK-2 receptors. Both the SP and the [MePhe 7]-neurokinin B data suggest that activation of a third neurokinin receptor subtype that is unaffected by an NK-1 receptor antagonist or an NK-2 receptor antagonist can cause contraction in guinea pig lung strips.

In vitro characterization of tripitramine, a polymethylene tetraamine displaying high selectivity and affinity for muscarinic M2 receptors.

1. The antimuscarinic effects of tripitramine were investigated in vitro in isolated driven left (force) and spontaneously beating right (force and rate) atria as well as in the ileum of guinea-pig and rat and in the trachea and lung strip of guinea-pig and compared with the effects of methoctramine. 2. Tripitramine was a potent competitive antagonist of muscarinic M2 receptors in right and left atria. The pA2 values ranged from 9.14 to 9.85. However, in the guinea-pig and rat left atria but not in guinea-pig right atria, tripitramine at lower concentrations (3-10 nM) produced a less than proportional displacement to the right of agonist-induced responses owing to the presence of a possible saturable removal process. 3. Tripitramine was about three orders of magnitude less potent in ileal and tracheal than in atrial preparations (pA2 values ranging from 6.34 to 6.81) which makes it more potent and more selective than methoctramine. 4. Another intriguing finding was the observation that the pA2 value of 7.91 observed for tripitramine in guinea-pig lung does not correlate with that found at both muscarinic M2 and M3 receptor subtypes, which clearly indicates that the contraction of guinea-pig lung strip is not mediated by these muscarinic receptor subtypes. 5. A combination of tripitramine with atropine resulted in addition of the dose-ratios for left atria as required for two antagonists interacting competitively with the same receptor site, whereas the same combination gave a supra-additive antagonism on guinea-pig ileum which suggests that tripitramine interacts with a second interdependent site. 6. Tripitramine was more specific than methoctramine since, in addition to muscarinic receptors, it inhibited only frog rectus abdominis muscular (pIC50 value of 6.14) and rat duodenum neuronal (pIC50 value of 4.87) nicotinic receptors among receptor systems investigated, namely alpha 1-, alpha 2-, and beta 1-adrenoceptors, H1- and H2-histamine receptors, and muscular and neuronal nicotinic receptors.

Cholinergic contraction of the guinea pig lung strip is mediated by muscarinic M 2-like receptors

The muscarinic receptor subtype mediating contraction of the guinea pig lung strip preparation was investigated and compared with that in guinea pig tracheal and human peripheral airway (small bronchi) smooth muscle preparations, using a number of subtype selective muscarinic receptor antagonists. It was found that guinea pig lung strip contraction was not mediated by a homogenous class of muscarinic M 3 receptors, in contrast to guinea pig tracheal and human peripheral airway smooth muscle. The affinities of the M 1- and M 3/M 2-selective muscarinic receptor antagonists on the guinea pig lung strip were between 0.35 and 1.94 log units lower than in the M 3 receptor tissues (respective pA 2 values on guinea pig lung strip and trachea: pirenzepine 6.36/6.71, AF-DX 474 6.39/7.11, AQ-RA 721 6.93/7.96, DAU 5884 6.78/8.72, UH-AH 371 7.04/8.20), whereas the affinities of the M 2/M 3-selective antagonists were between 0.63 and 1.97 log units higher (AF-DX 116 6.63/6.00, AQ-RA 741 7.48/6.63, gallamine 5.44/3.47, methoctramine 7.30/5.38). As a result, a good correlation was obtained when pA 2 values from guinea pig lung strip were compared to p K i values towards bovine cardiac muscarinic M 2 receptors, though it was noticed that pirenzepine and the M 3/M 2-selective antagonists showed a closer relationship than the M 2-selective compounds. These results suggest that cholinergic contraction of the guinea pig lung strip is mediated by muscarinic M 2-like receptors, possibly representing a novel subtype or a mixture of M 2 (cardiac) and M 3 (or M 4) subtypes. It remains to be established, however, on what structure in the lung these contractile M 2-like receptors are located and also by which transduction mechanism they produce contraction.

The thromboxane receptors of rat and guinea-pig lung

The thromboxane (TXA 2) receptors on rat and guinea-pig lung strips were compared using TXA 2 agonists and TXA 2 receptor antagonists. On rat lung strip several TXA 2 mimetics were full agonists whilst the primary prostanoids lacked agonist activity. On guinea-pig lung strip the same agonists displayed markedly different efficacies. Both preparations contained homogenous populations of TXA 2 receptors as evidenced by BAY u3405 giving comparable pA 2 values against four TXA 2 mimetics. However, the observed pA 2's of nine different TXA 2 receptor antagonists, determined against U46619, did not correlate between the two preparations. These results point to the existence of TXA 2 receptor subtypes.

The inhibition of [ 3H]leukotriene D 4 binding to guinea-pig lung membranes. The correlation of binding affinity with activity on the guinea-pig ileum

Guinea-pig lung membranes contain high affinity (K D = 0.8 nM) binding sites for [ 3H]leukotriene D 4 ([ 3H]LTD 4). The binding is inhibited by leukotriene antagonists, such as ICI 198615 and SK & F 104353, in a manner consistent with the Law of Mass Action at a single site. It is also inhibited by a range of leukotriene analogues in a dose-related manner. Inhibition by some of these e.g. LTC 4 suggests that the [ 3H]LTD 4 binding sites are heterogeneous. The binding affinity of the leukotriene analogues is significantly correlated (P < 0.001) to their spasmogenic activity on guinea-pig ileum but not on guinea-pig lung strip. The binding affinity of the leukotriene antagonists is also correlated to their antagonist activity on guinea-pig ileum (P < 0.05) but not on guinea-pig lung. These results indicate that the [ 3H]LTD 4 binding site in guinea-pig lung is similar to the leukotriene receptor activated by LTD 4 and LTE 4 on guinea-pig ileum. The contractile response of guinea-pig lung strips to leukotrienes, in the presence of indomethacin, is mediated by a distinct type of leukotriene receptor.

Identification and biological activity of dihydro-leukotriene B4: A prominent metabolite of leukotriene B4 in the human lung

Exogenous [3H]leukotriene B4 (LTB4) was converted into several polar and non-polar metabolites in the chopped human lung. One of the major metabolites was identified as 5(S),12-dihydroxy-6,8,14-eicosatrienoic acid (10,11-dihydro-LTB4) by means of co-chromatography with authentic standards, ultraviolet spectrometry and gas chromatography-mass spectrometry. Analysis on chiral straight phase HPLC revealed the presence of both the 12(S) and 12(R) epimers of dihydro-LTB4. Dihydro-LTB4 was also formed from endogenously generated LTB4 in ionophore A23187 stimulated incubations. The dihydro metabolites were approximately 100 times less potent than LTB4 in causing guinea pig lung strip contraction and leukocyte-dependent inflammation in the hamster cheek pouch in vivo.

Essential thiol and disulphide groups in the histamine H1-receptor signal transfer of guinea-pig parenchymal lung strips

Guinea-pig parenchymal lung strips contract after H1-receptor stimulation and membrane depolarisation with KCl. Contractions after 50 mM KCl were similar to the maximal histamine response. Treatment of lung strips with micromolar concentrations of the thiol-alkylator N-ethylmaleimide markedly affects both histamine H1-receptor mediated and 50 mM KCl-induced contractions. The H1-receptor response was only affected via a decrease in the maximal response. The response to 50 mM KCl was also inhibited after thiol-alkylation. However, H1-receptor responses appeared to be slightly more sensitive towards thiol-alkylation compared to KCl-responses. Reduction of disulphide groups with 1,4-dithiothreitol also modified the contractile responses to both stimuli. It is concluded that both thiol- and disulphide moieties play important roles in the regulation of histamine H1-receptor activity.

Inhibition of histamine release from human lung and rat peritoneal mast cells by cyclosporin-A

Cyclosporin A (CS-A) partly inhibited IgE-mediated histamine release from human lung tissue in vitro (chopped and collagenase-dispersed preparations). Inhibition started at concentrations within the clinical blood level of the drug, but the IC50 was much higher (10-50 microM; 50% inhibition reached only in some experiments). CS-A also inhibited histamine release from rat peritoneal mast cells (RPMC) induced by antigen, concanavalin-A (Con-A), compound 48/80 and ionophore A23187. The IC50 values were 0.3, 23.0, and 33.0 microM for Con-A, A23187 and ovalbumin respectively. Inhibition of 48/80-induced release did not reach 50%. By comparison with human basophils the human lung and RPMC were less sensitive to the inhibitory action of CS-A. The IgE-mediated Schultz-Dale reaction in human lung strips was slightly and inconsistently inhibited by CS-A, but IgG1-mediated reaction in guinea-pig lung strips was potentiated by the drug.

Ebselen inhibits contractile responses of guinea-pig parenchymal lung strips

Ebselen is a new anti-inflammatory drug with a wide spectrum of pharmacological activities. Since this compound might be useful in diseases related to airway inflammation we evaluated the effects of ebselen on the contractile responses of guinea-pig parenchymal lung strip. Ebselen and its sulfur analogue RP 62373 depressed both histamine H 1-receptor-mediated and KCl-induced (50 mM) contractions of guinea-pig lung strips equipotently. The responses to histamine were only affected via depression of the maximal response; treatment with 3 μM ebselen for 30 min resulted in depression to 77 ± 5% of the control value, whereas 10 and 30 μM inhibited the contractions to 53 ± 4 and 52 ± 4% of the control value respectively. The responses after membrane depolarisation (50 mM KCl) were less sensitive to ebselen pretreatment; 10 μM ebselen inhibited contractions by only 20%, whereas 30 and 100 μM depressed the response by approximately 50%. These observations were evaluated in the context of the activities of ebselen already described. The effects of lipoxygenase, cyclooxygenase, protein kinase C inhibition and thiol alkylation were studied, using established agents. However, although interaction with critical thiol groups might explain our data, the mode of action of ebselen is yet not fully elucidated.

Effect of Stobadine and Histamine H&lt;sub&gt;1&lt;/sub&gt; and H&lt;sub&gt;2&lt;/sub&gt; Blockers on Histamine–Induced Contraction of Guinea Pig Airways in vitro

Histamine, a nonselective histamine receptor agonist, activates simultaneously both H1 and H2 receptors in the guinea pig trachea and lung strip. The resulting contraction is due to the prevalence of H1 receptors, because they are blocked by the selective H1 antagonist diphenhydramine. The H2 receptor antagonists cimetidine and ranitidine increased the sensitivity of both tissues to histamine by affecting primarily the amplitude of contractions induced by high histamine concentrations. Since the lung strips were more sensitized by ranitidine and low concentrations of the other studied antagonists (diphenhydramine, dithiadene, stobadine) than the tracheal smooth muscle, it is inferred that the density of H2 receptors is higher in peripheral than central airways. From all the studied histamine receptor antagonists only dithiadene was able to unmask the relaxation induced by H2 receptor activation indicative of its highest H1 selectivity. In the light of the concentration-dependent antihistaminic effect of stobadine, i.e. potentiation in low and inhibition in high concentrations, stobadine is suggested to belong to antihistaminics with no histamine receptor subtype selectivity.

Identification of a novel 7- cis-11- trans-lipoxin A 4 generated by human neutrophils: total synthesis, spasmogenic activities and comparison with other geometric isomers of lipoxins A 4 and B 4

Addition of (15 S)-hydroxy-5,8,11- cis-13- trans-eicosatetraenoic acid (15-HETE) and the ionophore A23187 (2.5 μM) to human neutrophils led to the formation of both lipoxin A 4 and lipoxin B 4 as well as a novel 3,6,15-trihydroxyeicosatetraenoic acid. The new compound was identified using an improved isolation and detection system and its basic structure was determined by physical methods. On the basis of biosynthetic considerations, geometric isomers of lipoxin A 4 and lipoxin B 4 were prepared by total synthesis. Comparison of these synthetic materials with the neutrophil-derived product showed that the new compound is (5 S,6 R,15 S)-trihydroxy-9,11,13- trans-7- cis-eicosatetraenoic acid or the 7- cis-11- trans-isomer of LXA 4 (7- cis-11- trans-LXA 4). LXA 4, 11- trans-LXA 4, 7- cis-LXA 4 and 7- cis-11- trans-LXA 4 all evoked dose-dependent (0.1–10 μM) contractions of the guinea pig lung strip, whereas 6- cis-LXB 4 and 6- cis-8- trans-LXB 4 relaxed this preparation. LXA 4 and 7- cis-LXA 4 were approx. 10-times more potent than the compounds with 11- trans geometry. However, all four double-bond isomers of LXA 4 caused contractions which, based upon pharmacological evidence, appeared to involve specific activation of the same site as cysteinyl-containing leukotrienes. In conclusion, 7- cis-11- trans-LXA 4 was isolated and identified as a novel biologically active eicosanoid formed by human neutrophils.

Involvement of protein kinase C in the histamine H1-receptor mediated contraction of guinea-pig lung parenchymal strips.

In this study we investigated the role of protein kinase C (PKC) in the histamine H1-receptor mediated contraction of guinea-pig parenchymal lung strips. Lung strips contract after administration of the PKC activators phorbol-12-myristate-13-acetate (PMA) and dioctanoylglycerol. Prolonged stimulation (45 min.) with a high concentration of PMA abolished subsequent responses to PMA whereas H1-responses were only partially reduced. Administration of a PKC inhibitor (H-7) also led to an inhibition of H1-responses. Experiments with combined incubations with the PKC inhibitor H-7 and the Ca2+-entry blocker verapamil suggest that the PKC contribution to the response is possibly mediated via regulation of Ca2+ influx.

Effects of thromboxane A2 synthetase inhibitor, DP-1904 on the action of vasoactive substances in guinea pig trachea and lung tissue strips

Thromboxane A2 (TxA2) is a potent platelet aggregator and vascular or bronchial constrictor. DP-1904, a newly synthesized imidazol TxA2 synthetase inhibitor, is a potent and long-acting agent. The present investigation was conducted to explore the effect of DP-1904 on the contractile or relaxing responses in guinea pig trachea and lung tissue strips induced by various vasoactive substances. Fourteen guinea pigs, weighing 300-350 g, were sacrificed. Trachea and lungs were removed, cut spirally, set up in bioassay glass jackets and superfused with Krebs-Henseleit solution at 37 degrees C, saturated with oxygen and carbon dioxide. Contraction of tissues was detected by an isotonic transducer and displayed on a polyrecorder. Arachidonic acid-induced relaxing responses in guinea pig trachea strips were attenuated significantly by the continuous infusion of DP-1904 in a dose-dependent fashion. Arachidonic acid-induced contractile responses in guinea pig lung strips were attenuated significantly by the continuous infusion of DP-1904, dose-dependently. Acetylcholine-, histamine- and prostaglandin F2 alpha-induced contractile responses in guinea pig lung and trachea strips were attenuated significantly by the continuous infusion of DP-1904, dose-dependently. The above results suggest that DP-1904 might be a useful therapeutic agent for the treatment of chronic obstructive lung diseases.

Blockade by methylation inhibitors of the anaphylactic response of guinea‐pig lung strips

1. The combination of two methylation inhibitors 3-deazaadenosine (10(-4) or 4 x 10(-4) M) plus L-homocysteine (2 x 10(-4) M) caused a time-dependent inhibition of antigen-induced contraction, formation of thromboxane B2 (TxB2) and release of histamine from lung parenchyma strips taken from guinea-pigs actively sensitized with ovalbumin (OA). 2. The methylation inhibitors also prevented the lung strip contractions induced by the mediators platelet-activating factor (Paf-acether, 10(-6) M), leukotriene D4 (LTD4, 10(-8) and 3 x 10(-8) M), and in part to arachidonic acid (10(-6) and 10(-5) M), under conditions where the contractions to histamine (10(-6)-10(-4) M) were virtually unaffected. 3. TxB2 formation induced by these mediators or by OA was more affected by the methylation inhibitors than the lung strip contractions, indicating that prostaglandin formation is more sensitive to these inhibitors than the myotropic activity. In contrast, the suppressive effect of the methylation inhibitors on histamine secretion by parenchyma lung strips induced by OA followed the inhibition of the contraction. 4. These results show that inhibitors of methyltransferases interfere with the myotropic responses and with the release of mediators by actively sensitized guinea-pig lung strips stimulated with antigen, and suggest a major role for a methylation process in mediating the contraction of and mediator release by the lung parenchyma.