Role of 1,2-sn diacylglycerol in airway smooth muscle stimulated by carbachol

Activation of muscarinic receptors in airway smooth muscle leads to breakdown of membrane polyphosphoinositides. In agreement with others, we show here that muscarinic stimulation elicits inositol-1,4,5-triphosphate formation. In addition, we show that carbachol also elicits total diacylglycerol and 1,2-sn diacylglycerol accumulation in a specific and dose-dependent manner (EC50 values: 2.1 x 10(-8) M for 1,2-sn diacylglycerol). The time-course of inositol-1,4,5-triphosphate accumulation is compatible with that of the clonic phase of muscle contraction. Since this derivative can mobilize intracellular Ca2+ stores, it may play a second-messenger role in the initial phase of contraction. The time-course of diacylglycerol accumulation is compatible with the muscarinic-induced tonic phase of smooth-muscle contraction. Carbachol induces similar dose-dependent reductions in isoproterenol-induced muscle relaxation (EC50 values for relaxation concentration-response curves to isoproterenol: 3 x 10(-6) M and 2.1 x 10(-5) M, with carbachol at 10(-7) M and 10(-4) M, respectively), and increases in adenylate cyclase activity (EC50 values for the concentration-response to isoproterenol: 1.2 x 10(-6) M and 1.5 x 10(-5) M, with carbachol at 10(-7) M and 10(-4) M, respectively). Since it is known that carbachol-induced uncoupling of beta 2-adrenergic receptors is proportional to the breakdown of polyphosphoinositides, and that 1,2-sn diacylglycerol is a potent activator of protein kinase C, 1,2-sn diacylglycerol could be mediating the uncoupling of beta 2-adrenergic receptors, via activation of alpha-protein kinase C and subsequent phosphorylation of receptor, and/or cyclase, and/or G proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Furosemide inhibits bradykinin-induced contraction of human bronchi: role of thromboxane A2 receptor antagonism

Bradykinin contracts human isolated small bronchi through prostanoid release and subsequent TP receptor stimulation. Furosemide 10(-4) to 10(-3) M concentration dependently inhibited bradykinin- and the stable TP receptor agonist U-46619-induced contraction of human isolated small airways. The inhibitory effect of furosemide on U-46619-induced contraction involves competitive antagonism at TP receptors. Such an inhibition of TP receptors could a least partly explain the inhibitory effect of furosemide on bradykinin-induced contraction, and could be one of the mechanisms of the protective effect of furosemide in asthma.

Role of thromboxane A2 in bradykinin-induced human isolated small bronchi contraction

We previously demonstrated that the bradykinin-induced contraction of human isolated small bronchi is inhibited by indomethacin, capsaicin (N-methyl-N-6-nonenamide) and ruthenium red but not by tachykinin receptor antagonists. The thromboxane A2 receptor (TP receptor) antagonist GR32191 ((1R-(1 alpha(Z),2 beta,3 beta,5 alpha))-(+)-7-(5-(((1,1'-biphenyl)-4-yl)- methoxy)-3-hydroxy-2-(1-piperidinyl)cyclopentyl)-4-heptenoic acid, hydrochloride) (10(-10) to 10(-8) M) dose dependently inhibited the effect of bradykinin, suggesting the mediation of the TP receptor in the action of bradykinin. With higher concentrations of GR32191 (10(-7) and 10(-6) M) bradykinin induced a relaxation which was inhibited by indomethacin and by the bradykinin B2 receptor antagonist Hoe 140 (D-Arg0[Hyp3,Thi-5,D-Tic7,Oic8]bradykinin). The thromboxane A2 synthase inhibitor dazoxiben (4-(-2-(1H-imidazol-1-yl)ethoxy) benzoic acid hydrochloride) 10(-6) M inhibited the bradykinin-induced contraction, suggesting that thromboxane A2 was involved in TP receptor stimulation. The thromboxane A2 mimetic U-46619 (9,11-dideoxy-11 alpha,9 alpha-epoxy-methano-prostaglandin F2 alpha)-induced contraction of human distal bronchi was not inhibited by capsaicin and ruthenium red. Our data suggest that bradykinin contracts human isolated small bronchi through thromboxane A2 release. The inhibitory effect of ruthenium red and capsaicin on the bradykinin response may be due to inhibition of thromboxane A2 release or arachidonic mobilisation.

In vitro effects of HOE 140 in human bronchial and vascular tissue

Bradykinin is a potent inflammatory mediator which may be involved in various airway diseases. A selective and potent antagonist of the bradykinin B2 receptor has recently been discovered (HOE 140: D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin). The purpose of this study was to evaluate the potency of this compound in isolated human tissue (bronchus, pulmonary artery endothelium, umbilical artery and vein smooth muscle). Bradykinin induced contractions of the isolated human bronchus and umbilical artery and vein (the umbilical vessels were pretreated with indomethacin and L-nitro-arginine to inhibit prostaglandin and nitric oxide synthesis). It provoked an endothelium-dependent relaxation in the human pulmonary artery. HOE 140 was a non-competitive antagonist in human bronchial tissue (pKB: 8.19 +/- 0.30) and a competitive one in vascular tissue (pA2: 7.97 +/- 0.12, 8.16 +/- 0.16 and 8.00 +/- 0.11 in human pulmonary artery, umbilical artery and vein respectively). The effect of HOE 140 was selective as it did not influence the umbilical vein contractile response to serotonin and histamine. HOE 140 up to 3 x 10(-6) M was devoid of residual agonistic activity in the various human preparations studied. Furthermore, although the effects of HOE 140 were fully reversible, in isolated bronchial airways and umbilical veins, HOE 140 (10(-6) M) still possessed activity 1 h after being washed out in both tissues. Our results indicate that HOE 140 is a potent and potentially long-acting antagonist of the human bradykinin B2 receptor.

Beta 3-adrenoceptor agonists, BRL 37344 and SR 58611A, do not induce relaxation of human, sheep and guinea-pig airway smooth muscle in vitro

The existence of atypical- or beta 3-adrenoceptors has now been generally accepted. These receptors have been shown to be abundant in adipose tissue and in a number of gastrointestinal smooth muscle preparations. A recent study reported that beta 3-adrenoceptor stimulation mediated relaxation of isolated canine bronchial smooth muscle. The aim of the present study was to extend this observation to other species. We investigated the in vitro responses of guinea-pig, human and sheep bronchial smooth muscle to isoprenaline, salbutamol (a selective beta 2-adrenoceptor agonist), and BRL 37344 and SR 58611A (two presumably selective beta 3-adrenoceptor agonists). The preparations were precontracted to 60-70% of maximal tension with histamine 10(-6) M for guinea-pig and human bronchi, or acetylcholine 10(-6) M for sheep bronchi. In each species, SR 58611A produced a slight fall in tension of about 10% of the effects of theophylline (3 mM), but this decrease in tension was not significantly different from the spontaneous and weak relaxation observed with saline addition during the same duration of the experiment. These relaxations were not modified by either the nonselective beta-adrenoceptor antagonist propranolol or the selective beta 2-adrenoceptor antagonist ICI 118,551. In contrast, BRL 37344 induced a significant concentration-dependent fall in tension induced by both spasmogens. Its relaxant effects were inhibited both by propranolol and ICI 118,551 in human and guinea-pig airways, whereas on the isolated sheep bronchus BRL 37344-induced relaxations were only slightly, albeit significantly, reduced with either of the beta-adrenoceptor antagonists tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of okadaic acid on the human isolated bronchus

The effects of okadaic acid, a polyether derivative of a 38-carbon monocarboxylic fatty acid obtained from a culture of the marine dinoflagellate, Prorocentrum lima, were studied on the human isolated bronchus. In low concentrations (0.01 and 0.03 microM), okadaic acid had no significant effect of its own on the human isolated bronchus, but in higher concentrations (0.1-10 microM) it induced a series of contractions and relaxations. The first contraction was of low intensity (5% of maximum response to acetylcholine 3 mM) and occurred early. The second contraction had a higher amplitude (30% of maximum response to acetylcholine 3 mM) and reached its peak with okadaic acid 0.3 microM. At higher concentrations (1-10 microM), following a relaxation phase, a later rebound contraction occurred between 70 and 120 min and corresponded to 40% of the maximum response to acetylcholine 3 mM. In addition, okadaic acid inhibited or abolished the contractile response evoked by either KCl 60 mM or acetylcholine 3 mM with IC50 of 0.04 and 0.12 microM, respectively. The second contraction evoked by 0.3 microM okadaic acid was partially inhibited in the presence of the Ca2+ channel blocker, nicardipine 1 microM, or after incubation of the human bronchus in a Ca(2+)-free solution and it was completely abolished in the presence of CdSO4 0.1 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxant effects and durations of action of formoterol and salmeterol on the isolated human bronchus

The objective of this study was to evaluate the potency and efficacy (intrinsic activity) of formoterol and salmeterol and their duration of action in comparison with other beta-adrenoceptor agonists in isolated human bronchi. Human bronchi were obtained at thoracotomy from patients with lung cancer. Potency (-log of the concentration of drug inducing 50% of maximal relaxation (-log EC50)) and efficacy (maximal effect (Emax), % of response to theophylline 3 x 10(-3) mol.l-1) were determined by analysis of cumulative isometric concentration-response curves to beta 2-adrenoceptor agonists in bronchial rings at resting tone or contracted maximally with acetylcholine 10(-3) mol.l-1 to induce functional antagonism. The onset and duration of action of beta-adrenoceptor agonists were measured by assessing the relaxant activity of drugs on the basal tone of isolated bronchi. In terms of potency, the rank order of the substances studied was formoterol > fenoterol > or = salmeterol > or = isoprenaline > or = salbutamol > or = adrenaline > or = terbutaline. Formoterol was 150-200 times more potent than isoprenaline. On preparations contracted with acetylcholine 10(-3) mol.l-1 the intrinsic activity (IA) of salbutamol, terbutaline and salmeterol compared with that of isoprenaline ranged 0.62-0.66. Intrinsic activity was higher with formoterol (0.84) and fenoterol (0.75). The onset of action of formoterol (2.14 +/- 0.55 min, n = 11) was not significantly different from that of salbutamol (1.90 +/- 0.24 min, n = 8) but shorter than that of salmeterol (6.40 +/- 1.40 min, n = 10).(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxant effects and durations of action of formoterol and salmeterol on the isolated human bronchus

The objective of this study was to evaluate the potency and efficacy (intrinsic activity) of formoterol and salmeterol and their duration of action in comparison with other beta-adrenoceptor agonists in isolated human bronchi. Human bronchi were obtained at thoracotomy from patients with lung cancer. Potency (-log of the concentration of drug inducing 50% of maximal relaxation (-log EC50)) and efficacy (maximal effect (Emax), % of response to theophylline 3 x 10(-3) mol.l-1) were determined by analysis of cumulative isometric concentration-response curves to beta 2-adrenoceptor agonists in bronchial rings at resting tone or contracted maximally with acetylcholine 10(-3) mol.l-1 to induce functional antagonism. The onset and duration of action of beta-adrenoceptor agonists were measured by assessing the relaxant activity of drugs on the basal tone of isolated bronchi. In terms of potency, the rank order of the substances studied was formoterol > fenoterol > or = salmeterol > or = isoprenaline > or = salbutamol > or = adrenaline > or = terbutaline. Formoterol was 150-200 times more potent than isoprenaline. On preparations contracted with acetylcholine 10(-3) mol.l-1 the intrinsic activity (IA) of salbutamol, terbutaline and salmeterol compared with that of isoprenaline ranged 0.62-0.66. Intrinsic activity was higher with formoterol (0.84) and fenoterol (0.75). The onset of action of formoterol (2.14 +/- 0.55 min, n = 11) was not significantly different from that of salbutamol (1.90 +/- 0.24 min, n = 8) but shorter than that of salmeterol (6.40 +/- 1.40 min, n = 10).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of furosemide on prostaglandin synthesis by human nasal and bronchial epithelial cells in culture

Inhaled furosemide protects asthmatic subjects against bronchial obstruction caused by indirect provocants. We have attempted to correlate the protective effect of furosemide with its ability to alter prostaglandin (PG) synthesis by the airway epithelium. Human epithelial cells from nasal polyps and bronchi were cultured in DME-Ham's F12 medium with 10% fetal calf serum. Confluent cells (days 6 through 8) were incubated for 30 min in fresh medium, and the PGs in the supernatant were measured by radioimmunoassay. Spontaneous output (ng.ml-1.mg-1 cell protein) was as follows (mean +/- SEM): PGE2 = 7.74 +/- 2.10 (n = 12), PGF2 alpha = 1.66 +/- 0.12 (n = 15), 6-keto-PGF1 alpha = 4.32 +/- 1.37 (n = 11), PGD2 = 0.73 +/- 0.16 (n = 11) for bronchial cells and PGE2 = 7.24 +/- 0.80 (n = 32), PGF2 alpha = 1.38 +/- 0.12 (n = 17), 6-keto-PGF1 alpha = 6.79 +/- 2.50 (n = 15), PGD2 = 0.42 +/- 0.07 (n = 17) for nasal cells. Incubation with arachidonic acid (25 micrograms/ml) for 30 min significantly increased the amounts of the four PGs. Incubation with furosemide (10(-4) M) for 30 min caused a marked reduction in both basal and arachidonic acid-stimulated production of PGE2 and PGF2 alpha but did not reduce production of 6-keto-PGF1 alpha and PGD2. Incubation with bumetanide (10(-4) M) for 30 min did not modify the PGE2 synthesis by nasal epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotensin modulates cholinergic and noncholinergic neurotransmission in guinea-pig main bronchi in vitro

Guinea-pig main bronchi were stimulated transmurally in vitro by electrical field stimulation in the presence of indomethacin 10(-6) M, propranolol 10(-6) M and phosphoramidon 10(-5) M. Two contractile neurogenic responses were successively observed. The second noncholinergic contraction was concentration dependently inhibited or abolished by neurotensin whereas the first cholinergic contraction was only partially inhibited. SR 48692, a novel antagonist of neurotensin receptors, reduced the inhibition induced by neurotensin (pKB = 9.75) whereas levocabastine, an antagonist of low-affinity neurotensin receptors, did not significantly modify the inhibitory effects of neurotensin on both neurally-mediated contractions. These results demonstrate that neurotensin exerts an inhibitory effect on neurotransmission in guinea-pig airways. Furthermore, the present study shows that the newly developed neurotensin receptors antagonist, SR 48692, is a potent inhibitor of the neurotensin inhibitory effects on cholinergic and noncholinergic contractions induced by electrical field stimulation of the guinea-pig isolated main bronchus.

Effects of SR 48968 on the neuropeptide gamma-induced contraction of the human isolated bronchus

Neuropeptide gamma (NP gamma) induced a contractile response of the human isolated bronchus which was potentiated by the neutral endopeptidase inhibitor, phosphoramidon, but was not modified by atropine and indomethacin. NP gamma was 3.31-fold more potent than NKA. Contractile response curves to NP gamma were shifted to the right and maximal responses reduced by the non-peptide NK2-receptor antagonist, SR 48968. The pKB of SR 48968 (8.94 +/- 0.18, n = 15), calculated according to Kenakin (1987) was very close to that reported for [Nle10]-NKA (4-10), a specific agonist of neurokinin NK2-receptors (8.86 +/- 0.13, n = 13), suggesting that the contractile effects of NP gamma on the human isolated bronchus were mediated through NK2A-receptors.

The nicardipine-isoprenaline interaction in human and guinea-pig isolated airways

The effects of the dihydropyridine calcium antagonist nicardipine on the concentration-response curves of relaxant compounds acting through the adenylate-cyclase/cAMP system (isoprenaline, forskolin, adenosine and theophylline) or by the cGMP pathway (sodium nitroprusside) were studied on human isolated bronchus and guinea-pig isolated trachea. These effects were compared with those of nifedipine (a dihydropyridine derivative) and theophylline (a non-selective phosphodiesterase inhibitor). Nicardipine, in the range of 0.01 to 1 microM, significantly potentiated the relaxant effects of isoprenaline, forskolin, adenosine and theophylline, whereas the effects of sodium nitroprusside were significantly potentiated at 10 microM only. These results suggest that nicardipine behaves as an inhibitor of phosphodiesterases III and IV. One such effect may be involved in the potentiation of the isoprenaline relaxation of human and guinea-pig isolated airways.

Contractile effects of bradykinin on the isolated human small bronchus

Bradykinin (Bk) induced a contraction in all small bronchi samples (diameter, 0.5 to 1 mm) from 20 patients. pD2 was 7.7 +/- 0.1 (pD2 = -log EC50) and maximal effect (Emax) was 36.2 +/- 4.7% of the maximal response to acetylcholine. The B2 agonist [Hyp3TyrMe8]Bk contracted airway smooth muscle with a pD2 of 7.8 +/- 0.2 and an Emax of 39 +/- 9%. The B1 agonist [Sar1dPhe8desArg9]Bk induced only a weak contraction at 10(-6) M. The effect of Bk was abolished by the B2 (Hoe 140) but not by the B1 [Leu8desArg9]Bk receptor antagonist. Indomethacin 10(-6) M abolished Bk-induced contraction, suggesting that cyclooxygenase products are involved in Bk action. Capsaicin 10(-5) M, which selectively depletes C fibers from airway mediators through the ruthenium red pathway, and ruthenium red 10(-5) M significantly inhibited the concentration-response curves to Bk. However, tetrodotoxin (+/-)-CP-96,345, SR 48968, and atropine did not significantly affect Bk concentration-response curves, suggesting that nerve conduction, substance P (SP), neurokinin A (NKA), and acetylcholine release are not involved in Bk action. Our data indicate that Bk contracts human distal airway smooth muscle through the Bk B2 receptor and a cyclooxygenase pathway. This effect appears to involve capsaicin and ruthenium red pathways but neither acetylcholine nor NKA and SP release.

Effects of two beta 3-adrenoceptor agonists, SR 58611A and BRL 37344, and of salbutamol on cholinergic and NANC neural contraction in guinea-pig main bronchi in vitro

1. The aim of the present study was to investigate the type of adrenoceptor which modulates constriction of the guinea-pig isolated main bronchus in response to electrical field stimulation (EFS). Drugs used were salbutamol and two agonists reportedly selective for the putative beta 3-adrenoceptor: BRL 37344 and SR 58611A. 2. At basal tone, all three drugs induced relaxation, however, SR 58611A and BRL 37344 (10(-9) to 10(-6) M) relaxed guinea-pig isolated main bronchus more weakly than salbutamol (10(-9) to 10(-6) M). The effects observed at 10(-6) M were 43% +/- 9%, 63% +/- 4% and 98% +/- 1% of the maximal effect induced by theophylline (3 x 10(-3) M) for SR 58611A, BRL 37344 and salbutamol, respectively. 3. SR 58611A and BRL 37344 (10(-8) to 10(-6) M) did not significantly modify the cholinergic component of the response to EFS, but caused a concentration-dependent reduction of the nonadrenergic non-cholinergic (NANC) excitatory component (41.8% +/- 10.1% and 56.8% +/- 7.4% respectively at 10(-6) M, n = 6-7). Salbutamol (10(-9) to 10(-7) M) strongly inhibited both components, with 91.1% +/- 4.2% of inhibition for the NANC contraction and 62.0% +/- 5.2% of inhibition for the cholinergic contraction (10(-7) M, n = 7). 4. Whereas the inhibitory effects of salbutamol were strongly inhibited by both propranolol (10(-6) M) and ICI 118,551 (10(-6) M), those of BRL 37344 were only slightly, albeit significantly reduced by both propranolol and ICI 118,551, and those of SR 58611A were unaffected by treatment with either beta-adrenoceptor antagonist. An alpha2-adrenoceptor antagonist, yohimbine, did not influence the inhibitory effects of any of the beta-adrenoceptor agonists tested.5. Concentration-response curves to acetylcholine (10-8 to 10-3 M), [Nle10]NKA(4-10) (10-10 to10-6 M) and substance P (10- to 3 x 10-6 M) were also significantly shifted to the right by salbutamol(10-6 M), whereas SR58611A and BRL37344 (10-6 M) had no effect.6. These results suggest that the stimulation of putative beta 3-adrenoceptors exerts a specific prejunctional inhibitory action on NANC excitatory response induced by EFS of the isolated main bronchus of the guinea-pig. They also suggest that a beta2-adrenoceptor agonistic component may be involved in the effects of BRL 37344.

Antitussive effect of SR 48968, a non-peptide tachykinin NK2 receptor antagonist

The antitussive effects of SR 48968, a non-peptide tachykinin NK2 receptor antagonist, were investigated on citric acid-induced cough in the unanesthetized guinea-pig and compared with the effects of codeine. SR 48968 (0.01-0.3 mg/kg i.p.) inhibited in a dose-dependent manner the number of coughs induced by inhalation of an aqueous solution of citric acid with an ED50 of 0.1 mg/kg (0.17 mumol/kg). Under similar conditions, the codeine ED50 was 8 mg/kg (27 mumol/kg). Naloxone, an opioid receptor antagonist, abolished the effects of codeine but did not modify the effects of SR 48968. These data suggest that NK2 receptor stimulation might play an important role in the regulation of the cough reflex and that SR 48968 could be a potential antitussive agent.

Effects of rolipram and siguazodan on the human isolated bronchus and their interaction with isoprenaline and sodium nitroprusside

1 The effects of the selective inhibitors of cyclic AMP phosphodiesterase type IV (rolipram) and type III (siguazodan) and their interactions with isoprenaline and sodium nitroprusside have been studied in the human isolated bronchus. 2 On bronchi under resting tone rolipram was, in terms of potency (pD2 = 7.77 +/- 0.14, n = 8), very similar to isoprenaline (pD2 = 7.31 +/- 0.12, n = 12) and salbutamol (pD2 = 7.12 +/- 0.17, n = 10) and approximately 10 fold more potent than siguazodan (pD2 = 6.80 +/- 0.12, n = 6). In terms of efficacy (Emax, expressed as percentage of maximal effect induced by theophylline 3 mM), both rolipram and siguazodan were less efficient (Emax = 74 +/- 6.7%, n = 8 and 66 +/- 7.5%, n = 6, respectively) than isoprenaline (Emax = 98 +/- 0.4%, n = 12) and salbutamol (Emax = 83 +/- 2.4%, n = 10). 3 During precontraction induced by methacholine (3 x 10(-7) M) or acetylcholine (10(-3) M), concentration-response curves to rolipram and siguazodan were shifted to the right and maximal effects reduced. Rolipram was more potent than siguazodan and, in terms of efficacy, it was less active. 4. Rolipram 10(-8) and 10(-7) M but not siguazodan potentiated the effects of isoprenaline as shown by the shift to the left of the concentration-response curve to isoprenaline. Sodium nitroprusside-induced relaxation was not modified by either drug. 5. These results show that rolipram is a potent relaxant of the human isolated bronchus, potentiating the effects of beta-adrenoceptor stimulation and suggest that, as previously demonstrated in other species(guinea-pig, cow) (Tomkinson et al., 1993), there may be a connection between the beta2-adrenoceptor subtype, which predominate in human airway smooth muscle, and the cyclic AMP phosphodiesterase type IV.

Effect of molsidomine and linsidomine on the human isolated bronchus and the guinea-pig isolated trachea

The effects of molsidomine and its metabolite linsidomine were studied on the guinea-pig isolated trachea and on the human isolated bronchus. These effects were compared with those of nitrate derivatives (sodium nitroprusside, isosorbide dinitrate), theophylline, zardaverine and isoprenaline. Linsidomine exerted a relaxant effect similar to that of sodium nitroprusside on the two types of preparations precontracted with acetylcholine, histamine or potassium chloride. Molsidomine was about one-hundredth as potent as linsidomine, and less efficacious. The effects of the two substances were not modified by removal of the human bronchial epithelium. The concentration-response curves of linsidomine and sodium nitroprusside were significantly shifted to the right by methylene blue (3 x 10(-5) M) but the effects of isoprenaline were unmodified. The effects of linsidomine and sodium nitroprusside were potentiated specifically by zaprinast (10(-6)-10(-5) M), an inhibitor of type Ia or V phosphodiesterases, whereas the effects of isoprenaline were potentiated by zardaverine (10(-9)-10(-8) M), an inhibitor of class III and IV phosphodiesterases. The effects of all three substances (linsidomine, isoprenaline and sodium nitroprusside) were potentiated equally by theophylline (10(-5)-10(-4) M), a nonspecific inhibitor of phosphodiesterases. It is concluded that linsidomine is a potent relaxant of the smooth muscle of the guinea-pig isolated trachea and human isolated bronchus. In terms of potency and efficacy, its effect is much superior to that of the parent compound molsidomine. It is suggested that linsidomine acts, like nitrate derivatives, through the guanylate cyclase-cGMP system.

Influence of (+/-)-CP-96,345 and SR 48968 on electrical field stimulation of the isolated guinea-pig main bronchus

The aim of this study was to investigate the effects of (+/-)-CP-96,345 and SR 48968, two new nonpeptide antagonists of neurokinin NK1 and NK2 receptors, respectively, on the response of isolated guinea pig main bronchi to electrical field stimulation (EFS). Bronchi were stimulated transmurally with biphasic pulses (16 Hz, 1 ms, 320 mA for 10 s) in the presence of indomethacin (10(-6) M) and propranolol (10(-6) M). Two successive contractile responses were observed. Both responses were abolished by tetrodotoxin (10(-6) M) whereas only the first rapid phase was abolished by atropine (10(-6) M). The late and prolonged second phase was strongly reduced by the neurokinin A (NK2) receptor antagonist SR 48968 (10(-11) to 10(-8) M) with an EC50 of 0.056 nM and a maximal inhibition of 83.3 +/- 10.8% (10(-8) M, n = 4). This second response was partially inhibited by the substance P (NK1) receptors antagonist (+/-)-CP-96,345 (10(-8) to 10(-6) M). An incubation of 2 h was necessary for SR 48968 to inhibit the EFS-evoked noncholinergic contraction. These results confirm that EFS of guinea-pig bronchi involves stimulation of cholinergic and noncholinergic excitatory nerves and demonstrate that the new developed tachykinin receptors nonpeptide antagonists (+/-)-CP-96,345 and especially SR 48968 are potent inhibitors of the noncholinergic contraction induced by EFS of the isolated guinea-pig main bronchus.

Effects on the isolated human bronchus of SR 48968, a potent and selective nonpeptide antagonist of the neurokinin A (NK2) receptors

Tachykinins produce concentration-dependent contraction of the human isolated bronchus by stimulation of receptors that belong to the NK2 type. The aim of this study was to investigate the inhibitory effects of a new, potent, and selective nonpeptide antagonist of the neurokinin A (NKA) (NK2) receptors, SR 48968 [(S)-N-methyl-N-[4-acetylamino-4-phenylpiperidino-2-(3,4-dichlorophenyl) butyl]benzamide] on human isolated airways. Our experiments were performed on human isolated bronchi obtained from patients with lung cancer. Phosphoramidon, 10(-5) M, was added to the bath to inhibit neurokinin metabolism. SR 48968 induced a parallel shift to the right of the concentration-response (C/R) curves to [Nle10]-NKA(4-10), a specific NK2 receptor agonist. The antagonism was of the competitive type, with a pA2 of 9.40 +/- 0.19 (slope = 0.95 +/- 0.08, n = 13). The (R)-enantiomer of SR 48968 was 100-fold less potent and a noncompetitive antagonist (slope = 0.56 +/- 0.11, n = 8); pA2 and slope of the racemate were 8.86 +/- 0.21 and 1.09 +/- 0.21 (n = 7), respectively. Under similar conditions, racemic CP-96,345, a nonpeptide NK1 antagonist, did not modify the C/R curves to [Nle10]-NKA(4-10) until 10(-7) M. SR 48968 did not modify C/R curves to acetylcholine, histamine, KCI, or PGF2 alpha on the human isolated bronchus. Finally, SR 48968 shifted to the right C/R curves to substance P on isolated human bronchi, whereas racemic CP-96,345 was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Formoterol and salbutamol inhibit bradykinin- and histamine-induced airway microvascular leakage in guinea-pig

1. The effects of the beta 2-adrenoceptor agonists, salbutamol and formoterol, on the increase of microvascular permeability induced by histamine or bradykinin in guinea-pig airways have been studied in vivo. Extravasation of intravenously injected Evans blue dye was used as an index of permeability. The effects of salbutamol and formoterol on the increase in pulmonary airway resistance induced by histamine or bradykinin have also been studied. 2. The increase in pulmonary airway resistance induced by histamine or bradykinin was totally inhibited by salbutamol and formoterol. The ED50 of the two mediators were 0.59 +/- 0.21 (n = 5) and 0.20 +/- 0.14 (n = 5) micrograms kg-1 respectively for salbutamol, and 0.13 +/- 0.12 (n = 6) and 0.02 +/- 0.01 (n = 6) micrograms kg-1 respectively for formoterol. 3. Salbutamol (10 and 30 micrograms kg-1) and formoterol (1 and 10 micrograms kg-1) inhibited the increase of microvascular permeability induced by histamine (30 micrograms kg-1) in the guinea-pig airways. The inhibitory effect was predominant in the trachea and the main bronchi, with a maximum inhibition of 20 to 50%. The two drugs had little or no inhibitory effect on the other structures studied, viz. nasal mucosa, larynx, proximal and distal intrapulmonary airways. 4. Salbutamol and formoterol (1 and 10 micrograms kg-1) abolished the increase in microvascular permeability induced by bradykinin (0.3 micrograms kg-1). This inhibitory effect of two beta-adrenoceptor stimulants was predominant in the trachea and the nasal mucosa where it was observed with 1 microgram kg-1 of the beta-adrenoceptor agonists.In the main bronchi, and in the proximal and distal intrapulmonary airways, the effects of bradykinin were abolished by 10 pg kg- of formoterol and salbutamol.5. The effects of bradykinin, but not those of histamine, were significantly reduced (nasal mucosa, main bronchi and distal intrapulmonary airways) or abolished (trachea, proximal intrapulmonary airways) by morphine 10mgkg-1, i.v. These results suggest that an indirect effect, through non-adrenergic noncholinergic (NANC) nerves is involved in the action of bradykinin on the microvascular permeability.6. In conclusion, intravenously injected beta-adrenoceptor stimulants can inhibit, partially or totally, the increase of airways microvascular permeability induced by intravenous histamine or bradykinin. However, these effects require doses that are higher than those that inhibit the increase in pulmonary airway resistance induced by these mediators. As suggested by the results obtained with morphine, the higher efficacy of beta2-adrenoceptor agonists versus bradykinin may occur through activation of presynaptic receptors of the non-adrenergic non-cholinergic (NANC) nerves preventing release of inflammatory neuropeptides such as substance P and neurokinin A.

Contractile activity of big endothelin-1 on the human isolated bronchus

1. We have studied the contractile activity of the 39 amino acid precursor of endothelin-1 (ET-1), big endothelin-1 (big ET-1), on human isolated bronchi. The contribution of the metalloproteases, neutral endopeptidase (NEP) and angiotensin converting enzyme (ACE), in the presence or absence of the epithelium lining, by use of specific inhibitors, was also evaluated on the effects of big ET-1. 2. Big ET-1 elicited a potent contraction of human isolated bronchus. The -log EC50 value for big ET-1 was 7.53 +/- 0.08 (n = 11) and Emax 78.5 +/- 3.8% (% of ACh 3mM). 3. Incubation of human isolated bronchi with the NEP inhibitor phosphoramidon (10(-5) M) induced a rightward shift of the concentration-response curve induced by big ET-1 (10(-9) M to 3 x 10(-7) M). Similar results were observed when human bronchi were incubated with thiorphan (10(-5) M), but the shift to the right was significantly less (P less than 0.01) than that observed in the case of phosphoramidon (-0.35 +/- 0.05 vs -0.67 +/- 0.07 log unit). 4. The two inhibitors of angiotensin I converting enzyme (ACE), captopril or enalapril diacid, did not affect the concentration-response curve for contraction induced by big ET-1. 5. When the epithelium was removed, a leftward shift of the concentration-response curve of big ET-1 (10(-9) M to 3 x 10(-7) M) was observed. Incubation of human isolated bronchi with phosphoramidon or thiorphan (10-5M) or with enalapril diacid or captopril did not modify the leftward shift of the concentration-response curve for big ET-1 after epithelium removal.6. These results suggest that big ET-1 elicits potent contractile activity in the human isolated bronchus and that its effect is the consequence of the conversion to ET-1 by a phosphoramidon-sensitive metalloprotease which, although different from NEP and ACE, appears to be similar to the endothelinconverting enzyme (ECE) described in other studies in animals.

Neurokinin A (NK2) receptor revisited with SR 48968, a potent non-peptide antagonist

SR 48968, a new non-peptide antagonist of NK2 receptors, has been tested in a variety of isolated smooth muscle preparations from rats, guinea pigs, rabbits, hamsters and men, in order to assess its selectivity for NK2 receptors as well as its competitivity and specificity. The compound has been found to be inactive as a stimulant or relaxant in all preparations but to exert a potent, competitive antagonism, particularly in tissues obtained from rabbits (pA2 9.8-10.3), guinea pigs (10.5), rats (9.4-9.6), men (9.36-9.6) and hamsters (7.45-8.6). SR 48968 is therefore more active on the NK2A than on the NK2B receptor subtype and the human receptor is close to the NK2A subtype. SR 48968 exerts an antagonism of the competitive type and is therefore suitable for receptor classification despite its slow reversibility in vitro. The sensitivity of NK2A receptors to SR 48968 is at least 1000 times higher than those of NK1 and NK3 receptors. The compound does not affect the effects of bradykinin, angiotensin or bombesin. Because of its activity in human tissues, its potency and long duration of action, SR 48968 is a new promising pharmacologic and possibly therapeutic agent.

Separation and identification of the 4-hydroxyantipyrine sulphoconjugate

In a previous study we observed, during separation of total antipyrine metabolites by high-performance liquid chromatography and after enzymatic hydrolysis, an unidentified peak corresponding to an ionic compound with pyrazolinone features. In the present study, this compound was identified as the 4-hydroxyantipyrine sulphoconjugate, and its structure was definitively confirmed by gas chromatographic-mass spectrometric analysis and by the use of pure synthetic substance. We also demonstrated the inhibitory effect of sodium metabisulphite, a necessary preservative of urinary samples, on hydrolysis of this conjugate in the presence of sulphatases from Helix pomatia or Aerobacter aerogenes. This inhibitory effect makes it impossible to perform a global assay of antipyrine metabolites after enzymatic or chemical hydrolysis and confirms the value of direct assay of the 4-hydroxyantipyrine sulphoconjugate.

Influence of benzodiazepines on the response of the guinea-pig isolated trachea to the contractile action of adenosine

The effects of diazepam and other agonists of central or peripheral benzodiazepine receptors were studied on the contractile action of adenosine, 2-chloroadenosine and R-PIA (N6-(L-2-phenylisopropyl)-adenosine) on the guinea-pig isolated trachea. These effects were compared to those of dipyridamole. Diazepam 10(-7) to 10(-5) M potentiated the efficacy of adenosine; the maximal contractile effect of adenosine (% vs. acetylcholine 10(-3) M) was 20.4 +/- 4.2 (n = 21) in control conditions and 45.5 +/- 3.7 (n = 6; P less than 0.001) in the presence of diazepam 10(-5) M. Ro5-4864 (10(-7) to 10(-5) M) or alpidem (10(-7) to 10(-5) M), both agonists of peripheral benzodiazepine receptors, potentiated the contractile effects of adenosine to the same extent as diazepam. Clonazepam and zopiclone, both agonists of central benzodiazepine receptors, did not modify these effects. Antagonists of central (flumazenil) or peripheral (RP 52028) benzodiazepine receptors had no influence on the interaction between diazepam or Ro5-4864 and adenosine. Conversely, dipyridamole significantly reduced (10(-7) M) or suppressed (10(-6) M) the contractile effects of adenosine. The contractile effects of 2-chloroadenosine and R-PIA were weakly affected in presence of high concentrations of diazepam and dipyridamole. Epithelium removal potentiated the contractile effect of adenosine on the guinea-pig isolated trachea and increased the potentiating effect of diazepam. It is concluded that benzodiazepines and related compounds can potentiate the contractile effect of adenosine on the guinea-pig isolated trachea through the activation of a peripheral receptor for the benzodiazepines and the resulting inhibition of adenosine uptake.