The zig-zag tracheal strip

RETRACTED: Ameliorative potential of linagliptin and/or calcipotriol on bleomycin-induced lung fibrosis: In vivo and in vitro study

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted due to the authors’ plagiarism of text and images from the work of Eman Said Abd-Elkhalek, Hatem Abdel-Rahman Salem, Ghada Mohamed SuddeK, Marwa Ahmed Zaghloul and Ramy Ahmed Abdel-Salam, Faculties of Pharmacy and Medicine, Mansoura University, Mansoura, Egypt.

Synthesis, docking study and β-adrenoceptor activity of some new oxime ether derivatives

A new series of oxime ethers 4a–z was designed and synthesized to test the blocking activity against β₁ and β₂-adrenergic receptors. Docking of these ether derivatives into the active site of the identified 3D structures of β₁ and β₂-adrenergic receptors showed MolDock scores comparable to those of reference compounds. Biological results revealed that the inhibition effects on the heart rate and contractility are less than those of propranolol. Nevertheless, the two compounds 4p and 4q that displayed the highest negative MolDock score with β₂-adrenergic receptors showed β₂-antagonistic activity by decreasing salbutamol relaxation of precontracted tracheal strips, which indicates the importance of a chlorothiophene moiety in the hydrophobic region for best complementarity with β₂ receptors. On other hand, the presence of a homoveratryl moiety increases the MolDock score of the tested compounds with the β₁ receptor.

Bioassay-guided fractionation of a thymol-deprived hydrophilic thyme extract and its antispasmodic effect

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts from Thymus vulgaris L. and Thymus zygis L. are traditionally used for bronchitis, catarrhs of the respiratory tract and supportive treatment of pertussis. A potential spasmolytic effect is thought to be due to the presence of the monoterpenoid phenols thymol and carvacrol in the extract. Based on previous data the present investigation aimed to clarify if thymol-deprived thyme extracts (as been in use within German drug market) have antispasmodic activity. Additionally compounds responsible for this effect had to be identified.

MATERIALS AND METHODS

Thyme fluid extract was subsequently fractionated by FCPC, LPLC, and HPLC and compounds isolated were identified by spectroscopic methods. Bioassay testing was done by quantification of antispasmodic activity in the preconstricted rat smooth muscle trachea model against papaverin as positive control.

RESULTS

Thymol-deprived spissum extract (SE) had good antispasmodic activity (-37%, related to the maximum contraction). Bioassay-guided fractionation indicated that rosmarinic acid and apigenin do not contribute to this effect. Luteolin contributed significantly to the antispasmodic activity (-9%).

CONCLUSIONS

Thyme extracts have antispasmodic activity, which is at least due to synergistic effects of phenolic volatile oil compounds and the flavone luteolin. Specifications of thyme-containing preparations should refer to this flavone in addition to focusing on the volatile phenols.

Caffeic acid phenethyl ester attenuates IgE-induced immediate allergic reaction

Caffeic acid phenethyl ester (CAPE) is the active component of honey bee propolis extracts. The results of the current study demonstrate that CAPE attenuated immunoglobulin (Ig)E-mediated allergic response in mast cells. Oral administration of CAPE inhibited IgE-mediated passive cutaneous anaphylaxis. CAPE effectively reduced both histamine and serotonin (5-HT)-induced vascular permeability in rats. CAPE also reduced histamine and leukotrienes (LTs) release from isolated rat peritoneal mast cells. Moreover, CAPE suppressed contraction induced by histamine (3 × 10(-8)-3 × 10(-5) M), 5-HT (3 × 10(-9)-10(-6) M) and adenosine (3 × 10(-8)-10(-5) M) in guinea pig tracheal zigzag. These findings provide evidence that CAPE may serve as an effective therapeutic agent for allergic diseases.

Pharmacological and phytochemical study on a Sisymbrium officinale Scop. extract

ETHNOPHARMACOLOGICAL RELEVANCE

The aerial parts of Sisymbrium officinale Scop. are commonly used to treat airway ailments, moreover in antiquity the herbal drug was reputed to possess anticancer properties. The results obtained in present work support the traditional use and the properties ascribed to Sisymbrium officinale.

AIM OF THE STUDY

In order to give a scientific basis to the traditional uses of Sisymbrium officinale, this study was aimed to evaluate in vitro the myorelaxant activity, the antimicrobial properties and the antimutagenic effect of an aqueous dry extract of the aerial parts of the plant. A phytochemical characterization of the extract was also performed.

MATERIALS AND METHODS

The myorelaxant activity was studied against the contractions induced by carbachol, histamine and leukotriene C(4), in isolated guinea-pig trachea. The antimicrobial activity was tested against six bacteria and one yeast. The Ames test, performed by the preincubation method, was used to study the antimutagenic activity of the extract by its capability to inhibit the mutagenic effect of 2-nitrofluorene, sodium azide, methyl methanesulfonate and 2-aminoanthracene, in Salmonella typhimurium TA98, Salmonella typhimurium TA100 and Escherichia coli WP2uvrA strains. The chemical composition of the extract was analyzed by TLC and HPLC.

RESULTS

Sisymbrium officinale showed to reduce the chemically-induced contractions of isolated guinea-pig trachea with major potency against leukotriene C(4) and histamine. The extract did not show any antibacterial activity. The Ames test showed a strong antimutagenic activity against 2-aminoanthracene, in Escherichia coli WP2uvrA and in Salmonella typhimurium TA98 strains. The phytochemical study highlighted the presence of putranjivine, the glucosinolate marker of Sisymbrium officinale, and of proline.

CONCLUSIONS

The myorelaxant activity of Sisymbrium officinale offers a scientific basis to its use in traditional medicine. The strong antimutagenic effect suggests further studies to evaluate its possible chemopreventive activity.

Antispasmodic activity of an extract from Plantago lanceolata L. and some isolated compounds

An ethanolic spissum extract of the aerial parts of Plantago lanceolata L. was examined for antispasmodic activity on isolated ileum and trachea of the guinea-pig. Isolated constituents were investigated as well. The P. lanceolata extract inhibited the contractions of the guinea-pig ileum that were induced by various agonists such as acetylcholine (ACh), histamine, potassium and barium ions. Additionally the trachea contractions induced by barium ions were inhibited. The compounds luteolin, acteoside, plantamajoside an catalpol peracetate but not catalpol, isoacteoside, lavandulifolioside and aucubin inhibited the ACh-induced contractions of the guinea-pig ileum. Luteolin and acteoside reduced the barium-induced contractions of the guinea-pig trachea. Two recently isolated compounds did not show antispasmodic activity: luteolin-3',7-diglucuronide and beta-hydroxy-acteoside.

New beta-adrenergic agonists used illicitly as growth promoters in animal breeding: chemical and pharmacodynamic studies

Clenbuterol and beta-adrenergic receptor agonist drugs are illegally used as growth promoters in animal production. Pharmacologically active residues in edible tissues led to intoxication outbreaks in several countries. Pressure of official controls pulsed synthesis of new compounds to escape analytical procedures. We report two new compounds named 'A' and 'G4', found in feeding stuffs. Chemical structure was studied through nuclear magnetic resonance-imaging and infrared spectroscopy, and beta(1)- and beta(2)-adrenergic activity was evaluated on isolated guinea-pig atrium and trachea in comparison with clenbuterol. Both compounds share with clenbuterol an halogenated aromatic ring with a primary amino group. Main modifications consisted of substitution of secondary amino group with an alkyl chain in compound A and substitution of the ter-butyl group with a benzene ring in compound G4. In guinea-pig trachea these compounds showed myorelaxant potency lower than clenbuterol (EC(50) was 43.8 nM for clenbuterol, 11700 nM for compound A, 2140 nM for G4). On the contrary, in the guinea-pig atrium (heart-beat rate stimulant effect) the compounds were more potent than clenbuterol (EC(50) was 15.2 nM for clenbuterol, 3.4 nM for compound A, 2.8 nM for G4). These pharmacodynamic properties, and stronger lipophilic properties shown by the two compounds may result in increased cardiovascular risk for consumers of illicitly treated animals.

R+-methanandamide inhibits tracheal response to endogenously released acetylcholine via capsazepine-sensitive receptors

The effects of cannabinoid drugs on the cholinergic response evoked by electrical field stimulation (0.2 ms pulse width, 20 V amplitude, 10 Hz, 7.5 s train duration) in guinea-pig tracheal preparations were investigated. The stable analogue of the endocannabinoid anandamide, R(+)-methanandamide (10(-7)-10(-4) M), produced a dose-dependent inhibition (up to 27+/-5% of control) of electrical field stimulation-mediated atropine-sensitive response. This effect was not blocked by the selective cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3 carboxamide hydrochloride (SR 141716A; 10(-6) M), and was not reproduced with the cannabinoid CB(1)/CB(2) receptor agonist R(+)-[2,3-dihydro-5-methyl-[(morpholinyl)methyl]pyrrolo [1,2,3-de]-1,4-benzoxazin-6-yl]-(1-naphthalenyl)methanone mesylate) (WIN 55,212-2; 10(-8)-10(-5) M) or the cannabinoid CB(2) receptor selective agonist 1-propyl-2-methyl-3-(1-naphthoyl)indole (JWH-015; 10(-8)-10(-5) M); it was, on the contrary, antagonized by the vanilloid antagonist 2-[2-(4-chlorophenyl)ethyl-amino-thiocarbonyl]-7,8-dihydroxy-2,3,4,5-tetrahydro-1H-2 benzazepine (capsazepine; 10(-6) M). At the postjunctional level, neither R(+)-methanandamide nor WIN 55,212-2 nor JWH-015 did affect tracheal contractions induced by exogenous acetylcholine (10(-6) M). An inhibitory vanilloid receptor-mediated effect on the cholinergic response evoked by electrical stimulation was confirmed with the vanilloid agonist capsaicin, at doses (3-6 x 10(-8) M) which poorly influenced the basal smooth muscle tone of trachea. In conclusion, our data indicate that in guinea-pig trachea (a) neither CB(1) nor CB(2) cannabinoid receptor-mediated modulation of acetylcholine release occurs; (b) vanilloid VR1-like receptors appear involved in R(+)-methanandamide inhibitory activity on the cholinergic response to electrical field stimulation.

The monoterpene alkaloid cantleyine from Strychnos trinervis root and its spasmolytic properties

Cantleyine, a monoterpene alkaloid isolated from the root bark of Strychnos trinervis, was submitted to a broad spectrum pharmacological screening, in which the principal effect observed was a nonspecific relaxation of isolated smooth muscles. Cantleyine relaxed (IC50 2.1 x 10(-4) M) the guinea-pig trachea, pre-contracted by carbachol and antagonized in a nonspecific manner; carbachol (IC50 2.1 x 10(-4) M) and histamine (IC50 1.4 x 10(-4) M) induced contractions in the guinea-pig ileum; and phenylephrine (IC50 3.8 x 10(-4) M) responses in the rat aorta. Cantleyine antagonized (pD'2, 3.82) cumulative concentration response curves to histamine in the ileum in a noncompetitive, reversible (slope, 4.84) and concentration dependent manner. The tonic contractions induced by histamine and KCl were also inhibited in a concentration-dependent and reversible manner (IC50 7.2 x 10(-5) and 1.8 x 10(-4) M, respectively), suggesting that cantleyine should be acting on voltage-dependent Ca2+ channels. This hypothesis was confirmed by the observation that cantleyine inhibited (pD'2, 3.35), in a concentration dependent manner, the CaCl2 induced contraction in depolarizing medium. These results suggest that cantleyine produces nonspecific spasmolytic effects in smooth muscle and that in guinea-pig ileum this effect is, in part, due to the inhibition of Ca+2 influx through voltage-dependent Ca2+ channels.

Anti-inflammatory and bronchodilator properties of KF19514, a phosphodiesterase 4 and 1 inhibitor

We investigated the effects of KF19514 (5-phenyl-3-(3-pyridyl)methyl-3H-imidazo[4,5-c][1,8]naphthyridin-4 (5H)-one) on bronchoconstriction and allergic inflammation in guinea pigs and on tumor necrosis factor-alpha production in mice. KF19514 inhibited phosphodiesterase 4 (IC50 = 0.40 microM) and phosphodiesterase 1 (IC50 = 0.27 microM) derived from canine tracheal smooth muscles. KF19514 relaxed contracted tracheal smooth muscle and had a potent inhibitory effect on antigen-induced bronchoconstriction (EC50 = 0.058 microM) in vitro. Intravenous administration of KF19514 inhibited histamine-induced bronchoconstriction (ID50 = 2.8 microg/kg i.v.). Moreover, oral administration of KF19514 inhibited anaphylactic bronchoconstriction (ID50 = 0.2 mg/kg p.o.), and eosinophil infiltration in airway stimulated with platelet-activating factor (PAF) or antigen. KF19514 also produced a significant inhibition of tumor necrosis factor-alpha production in mice (ID50 = 0.023 mg/kg p.o.). Finally, KF19514 completely inhibited antigen-induced hyperreactivity at 0.1 mg/kg p.o. These results demonstrate that KF19514 may have efficacy in the treatment of asthma.

Stereoselective action of (R*,R*)-(+/-)-methyl-4-[2-[2-hydroxy-2-(3-chlorophenyl)ethylamino] propyl]-phenoxyacetic acid (BRL37344) on beta-adrenoceptors and metabolic chiral inversion

Stereoisomers of BRL37344 ((R*,R*)-(+/-)-methyl-4-[2-[2-hydroxy-2 -(3-chlorophenyl)ethylamino]propyl]-phenoxyacetic acid), a beta 3-adrenoceptor agonist, were synthesized and separated with good resolution by derivatization with 1-anthroyl cyanide prior to chiral HPLC. Agonist effects on rat right atria, guinea pig trachea, and rat brown adipocytes were due principally to the (RR) isomer, while other isomers (SS, RS, and SR) were much less potent or inactive. Since the racemate (RR +/- SS) was half as potent as the (RR) isomer in all specimens tested, the (SS) isomer does not appear to have antagonistic effects. When [14C](RR)BRL35135A ((R*,R*)-(+/-)-methyl-4-[2-[2-hydroxy-2-(3-chlorophenyl)ethylamino]propy l] -phenoxyacetate hydrobromide), the HBr salt of the methyl ester of BRL37344, was administered orally to male Wistar rats, both the (RR) and (SR) isomers of [14C]BRL37344 were detected in plasma, while only the (SS) isomer of [14C]BRL37344 was detected after [14C](SS)BRL35135A administration. These findings indicate that there is clear stereoselectivity in the effects of BRL37344 on beta-adrenoceptors, and that stereoselective chiral inversion from the RR isomer to the SR isomer occurs in rats.

Acetylcholine-induced bronchoconstriction modified by noise exposure in normal but not in sensitized guinea-pigs

1. The acute (6h) exposure of guinea-pigs to white noise (110 dB) as a stress stimulus, reduced bronchial reactivity to acetylcholine (Ach) (3-1000 micrograms kg-1 i.v.) in anaesthetized animals. 2. The hyporesponsiveness to Ach in stressed animals was not confirmed in vitro on tracheal preparations (Ach 1 x 10(-9)-1 x 10(-4) g ml-1) and disappeared in vivo when the animals were sensitized with ovalbumin (OA, 100 mg kg-1 i.p. + 100 mg kg-1 s.c.). The hyporesponsiveness was also absent in ovalbumin sensitized guinea-pigs exposed to an aerosol of ovalbumin 60 min before testing with Ach. 3. In non-sensitized guinea-pigs, pretreatment with butoxamine (1 mg kg-1 i.v.) or with theophylline (25 mg kg-1 i.v.), completely abolished the effect of noise-exposure. In contrast, pretreatment with L-NG-nitro-arginine methyl ester (L-NAME, 10 mg kg-1 i.v.), alpha-chymotrypsin (2 U kg-1 i.v.) or with enprofylline (10 mg kg-1 i.v.), did not affect it. 4. In conclusion, our experiments reveal inhibitory mechanisms upon Ach-induced bronchoconstriction activated by a stress stimulus and this is absent in sensitized animals. These mechanisms seem to be linked to the adrenergic beta 2-receptors and a role for the purinergic system (via A-receptors) may also be present.

Involvement of the M2 muscarinic receptor in contractions of the guinea pig trachea, guinea pig esophagus, and rat fundus

The involvement of the M2 muscarinic receptor in contractile responses of the guinea pig trachea, guinea pig esophagus, and rat fundus was investigated. In the standard assay, oxotremorine-M elicited contractions of the trachea with an EC50 value of approximately 73 nanoM.--2- -(Diethylamino)methyl- -1-piperidinyl-acetyl--5,11- dihydro-6H-pyrido-2,3-b--1,4- benzodiazepine-6-one (AF-DX 116) at 1 and 10 microM antagonized these contractions by 2.1- and 9.0-fold increases in the EC50 value for oxotremorine-M. These effects are consistent with antagonism of an M3-mediated contractile response. In subsequent experiments, the M3 receptors were first inactivated selectively by incubation with N-(2-chloroethyl)-4- piperidinyl diphenylacetate (4-DAMP mustard) (40 nanoM) for 1 hr in the presence of AF-DX 116 (1 microM) followed by extensive washing. In 4-DAMP mustard treated trachea, oxotremorine-M elicited contractions with an EC50 value of 0.31 microM in the presence of histamine (10 microM) and forskolin (4 microM). Under these conditions, AF-DX 116 at 1 and 10 microM antagonized contractions to oxotremorine-M by 8- and 59-fold increases in the EC50, respectively, while para- fluorohexahydrosiladiphenidol(p-F-HHSiD) (0.1 microM) had no effect. These effects are consistent with a contraction being mediated by an M2 receptor. In the guinea pig esophagus and rat fundus, AF-DX 116 and p-F-HHSiD blocked contractions measured under similar conditions with magnitudes intermediate between what would be expected from an M2 and an M3 receptor, suggesting that perhaps both subtypes contribute to the overall contractile response under these conditions. In addition, contractions of the guinea pig trachea measured in the presence of histamine and forskolin were pertussis toxin sensitive. These results that, in the trachea, M2 receptors can dominate the contractile response after a majority of the M3 receptors have been inactivated, whereas in the guinea pig esophagus and rat fundus, M2 receptors may contribute to, but do not play a dominant role in the overall response.

The (S)-(+)-enantiomer of dimethindene: a novel M2-selective muscarinic receptor antagonist

The present study was designed to determine to determine the in vitro affinity profile of (R)-(-)-dimethindene and (S)-(+)-dimethindene at muscarinic receptor subtypes using both functional and binding assays. In addition, the racemate was investigated in functional studies. The functional muscarinic receptors studied were putative M1 receptors in rabbit vas deferens and rat duodenum, M2 receptors in guinea-pig left atria and rabbit vas deferens, as well as M3 receptors in guinea-pig ileum and trachea. Furthermore, the histamine H1 antagonism by (R)-(-)- and (S)-(+)-dimethindene has been examined in guinea-pig ileum. Muscarinic binding selectivity was assessed in homogenates from human neuroblastoma NB-OF 1 cells (M1), rat heart (M2), pancreas (3) and striatum (M4). The results demonstrate that (S)-(+)-dimethindene is a potent M2-selective muscarinic receptor antagonist (pA2 = 7.86/7.74; pKi = 7.78) with lower affinities for the muscarinic M1 (pA2 = 6.83/6.36; pKi = 7.08), the M3 (pA2 = 6.92/6.96; pKi = 6.70) and the M4 receptors (pKi = 7.00), respectively. The (S)-(+)-enantiomer was more potent (up to 41-fold) than the (R)-(-)-enantiomer in all muscarinic assays. In contrast, the stereoselectivity was inverse at histamine H1 receptors, the (R)-(-)-enantiomer being the eutomer (pA2 = 9.42; pA2/(S)-isomer = 7.48). In conclusion, (S)-(+)-dimethindene is a useful tool to investigate muscarinic receptor heterogeneity. In addition, this lipophilic compound might become the starting point for the development of M2-selective muscarinic receptor antagonists useful as diagnostic tools for quantifying muscarinic M2 receptors in the central nervous system with positron emission tomography imaging, and to test the hypothesis that muscarinic M2 receptor antagonists show beneficial effects in the treatment of cognitive disorders.

Beta-adrenoceptor regulation and functional responses in the guinea-pig following chronic administration of the long-acting beta 2-adrenoceptor agonist formoterol

Formoterol is a long acting beta 2-adrenoceptor agonist designed for the alleviation of the symptoms of asthma. This study examined the effects of 14 day administration of formoterol (200 micrograms/kg/day i.p.) on beta 1- and beta 2-adrenoceptors in guinea-pig cardiac and lung tissue. Quantitative autoradiography was used to measure changes in receptor density and organ bath studies determined alterations in functional response. Formoterol treatment produced marked reductions of between 43% and 77% in beta 2-adrenoceptor density in all regions of the heart (atrioventricular node, bundle of His, right and left bundle branches, interventricular and interatrial septa, right and left atria, ventricles and apex) and lung (bronchial and vascular smooth muscle and parenchyma) (P < 0.01, n = 6). beta 1-Adrenoceptor density remained unchanged in all cardiac and lung regions. In functional studies (-)-isoprenaline was 4 fold less potent at causing relaxation of carbachol (1 microM) precontracted tracheal smooth muscle (pD2: control 8.49 +/- 0.03, formoterol 7.91 +/- 0.10, P < 0.001, n = 4), but formoterol treatment did not change the ability of (-)-isoprenaline to elicit a maximum response. The pKB values for ICI 118,551, 7.33 +/- 0.08 in the control and 7.20 +/- 0.01 in formoterol treated animals, were between those expected for beta 1- and beta 2-adrenoceptors suggesting involvement of both subtypes in the response. In spontaneously beating right atria and electrically paced left atria, tissues in which responses are largely mediated by beta 1-adrenoceptors, there was no significant change in responses to (-)-isoprenaline (right atria pD2: control 8.45 +/- 0.02; formoterol 8.42 +/- 0.11; P = 0.77, n = 4) (left atria pD2: control 8.25 +/- 0.03; formoterol 8.47 +/- 0.08; P = 0.09, n = 4). In the presence of CGP 20712A (100 nM) the pKB values did not change with formoterol treatment (left atria: control 9.59 +/- 0.12, formoterol 9.66 +/- 0.12; P = 0.70, n = 4) (right atria: control 8.93 +/- 0.11, formoterol 9.11 +/- 0.07; P = 0.25, n = 4). The doses and route of administration of formoterol used in this study differs from those used clinically. However, this study demonstrates that chronic formoterol administration produces selective down-regulation of beta 2-adrenoceptors in the lung and heart. The changes in the lung are accompanied by a shift to the right in the concentration-response curve to beta-agonist stimulation with no change in the maximum response.

A pharmacological analysis of receptors mediating the excitatory response to 5-hydroxytryptamine in the guinea-pig isolated trachea

1. Experiments were carried out to characterize the receptors mediating the indirect excitatory response to 5-hydroxytryptamine (5-HT) in the guinea-pig isolated trachea. 2. 5-HT caused concentration-dependent contractions of tracheal strips, and the resulting concentration-response curve was biphasic in nature. The first phase was obtained with agonist concentrations in the range of 0.01-3 nM and achieved a maximum which was 30% of the total 5-HT response, while the second phase was in the range 10 nM-1 microM. 3. Atropine (0.1 microM) and tetrodotoxin (TTX: 0.3 microM) significantly reduced both phases of the 5-HT curve. Morphine (10 microM), which can act to inhibit neuronal acetylcholine release, abolished the first phase and reduced the second phase. This suggests that the first phase is mainly neurogenic (cholinergic) in nature, while the second phase is in part neurogenic and in part due to direct activation of the effector cells. 4. The 5-HT2A receptor antagonist, ketanserin (0.01, 0.1 microM) markedly depressed the first phase and shifted the second phase to the right in a parallel manner, with some depression of the 5-HT response maximum. The less selective (5-HT1/5-HT2A) antagonist, methiothepin (0.1 microM) mimicked the action of ketanserin, albeit with less potency. Concomitant administration of ketanserin and methiothepin (each at 0.1 microM) produced an antagonism similar to that caused by ketanserin (0.1 microM) alone. 5. The 5-HT3 receptor antagonists, ondansetron (0.1 microM) and granisetron (0.01 microM) slightly but significantly inhibited the first phase of the 5-HT curve without altering the second phase. SDZ 205,557(0.3 MicroM), a 5-HT4 receptor antagonist, was ineffective.6. Our results suggest that neural 5-HT2A and, to a lesser extent, 5-HT3 receptor subtypes mediate the first phase of the 5-HT curve in the guinea-pig trachea. The second phase is mediated by 5-HT2Areceptors, which are probably located at both the neural and muscular level. No evidence for the participation of 5-HT1 receptors in the 5-HT response has been obtained.

Selectivity of LG50643 for postjunctional muscarinic-receptor subtype in the guinea-pig trachea

The effects of (+/-)-LG50643, a new N-quaternary tropinic ester of phenylcyclohexene carboxylic acid, endowed with a potent antimuscarinic activity, have been investigated on muscarinic receptor-mediated responses of the guinea-pig trachea to electrical field stimulation. An isolated preparation which allows the simultaneous measurement of tritiated acetylcholine release (prejunctional effect) and smooth muscle contraction (postjunctional effect) was used. The guinea-pig epithelium-deprived trachea was stimulated with 500 pulses (20 Hz, 1 ms, 9 V for 5 s, 30 s apart) in the presence of indomethacin (1 microM). Three successive pre- and postjunctional responses were observed. The potencies (-logEC50) of (+/-)-LG50643 for pre- and postjunctional muscarinic receptors were determined and compared with those of selective muscarinic antagonists. In addition, the affinity values of (+/-)-LG50643 for muscarinic-receptor subtypes were determined in radioligand binding experiments in cerebral cortex, heart and salivary glands of rat as target tissues for M1, M2 and M3 receptors, respectively. The results obtained in both functional and binding assays indicate (+/-)-LG50643 is a potent and selective antagonist for the M3-receptor subtype.

Pharmacological studies on Aristolochia papillaris Mast. (Aristolochiaceae)

The non-specific and reversible smooth muscle relaxant activities of the ethanolic extract (EE) of Aristolochia papillaris Mast., a fraction of EE containing tertiary alkaloids (TAF) and of 3 compounds isolated from TAF are reported. In the non-pregnant rat uterus, EE and TAF inhibited both the oxytocin-induced contractions and the amplitude of rhythmic spontaneous contractions. The IC50 values for EE and TAF were 0.91 and 0.22 microgram/ml, respectively in the first experiments while the corresponding values were 1.0 and 0.17 microgram/ml in the second case. The rhythmic contractions of the uterus obtained from 21-day pregnant rats were also reduced by EE and TAF with IC50 values of 25.5 and 11.2 micrograms/ml, respectively. The relaxation of isolated guinea pig trachea produced by EE and TAF were also observed with the compounds moupinamide, coclaurine and isoboldine isolated from TAF. The IC50 values of these compounds were 1.58 x 10(-4) M, 3.98 x 10(-4) M and 7.10 x 10(-4) M, respectively. Propranolol significantly antagonized the effects of coclaurine and isoboldine but failed to inhibit the responses to moupinamide which suggests that the plant constituents produce muscle relaxation by beta-adrenoceptor-dependent and -independent mechanisms.

Antagonist effect of losartan on angiotensin II induced contraction in five isolated smooth muscle assays

Antagonist effect of losartan, a nonpeptide antagonist of angiotensin II, on angiotensin II induced contractile response was studied in five isolated smooth muscle assays. In the rabbit aorta and guinea-pig stomach assays, losartan competed with angiotensin II for the angiotensin receptors in an apparently simple manner, that is compliance with the basic criteria of Schild analysis for simple competition. Noncompliance, however, was observed in the guinea-pig ileum, rat ileum and guinea-pig trachea assays where losartan induced nonparallel rightward shifts of angiotensin II E/log[A] curves and the Schild plots were found to have slopes greater than unity. The observed deviations from simple competitive antagonism appeared to be different from those reported earlier, and a possible explanation involving tissue-dependent noncompetitive factor(s) is discussed.

Inhibition of beta-adrenoceptor agonist relaxation of airway smooth muscle by Ca(2+)-activated K+ channel blockers

In isolated guinea pig trachea contracted by 0.5 mM acetylcholine, the cumulative relaxant concentration-response curves to the beta 2-adrenoceptor agonist, salbutamol, were shifted to the right by depolarizing concentrations of KCl, as well as by charybdotoxin, iberiotoxin and tetraethylammonium ion, which are antagonists of the high-conductance Ca(2+)-activated K+ channel. The shifts produced by KCl (40 mM), charybdotoxin (100 nM), iberiotoxin (50 nM), and tetraethylammonium ion (2 mM) were approximately 230-fold, 10-fold, 78-fold, and 8-fold, respectively. The blockade of beta 2-adrenoceptor agonist-induced relaxation by these agents was totally reversed by 0.3 microM nifedipine. Similar reversal was obtained with either 100 microM CdCl2, or low Ca2+ (50 microM) Krebs medium. These data suggest that charybdotoxin, iberiotoxin and tetraethylammonium ion, like KCl, cause membrane depolarization which in turn activates voltage-dependent Ca2+ channels. The influx of Ca2+ via these channels provides an additional mode to that of release of intracellular Ca2+ evoked by acetylcholine for maintaining cell Ca2+ concentration at a high level. This is apparently sufficient to account functionally for the blockade of beta 2-adrenoceptor agonist-induced relaxation. In view of this interpretation regarding the action of Ca(2+)-activated K+ channel antagonists, earlier proposals ascribing the relaxant effect of beta 2-adrenoceptor agonists strictly to activation of these channels must be reevaluated.

Characterization of the interaction of the cervane alkaloid, imperialine, at muscarinic receptors in vitro

The action of the cervane alkaloid, imperialine, has been assessed at M1, M2 and M3 receptors in functional assays and at M1, M2, M3 and putative M4 sites in binding studies. In functional studies, imperialine acted as a selective surmountable antagonist at M2 receptors in guinea-pig isolated atria and uterus (-log KB = 7.7 and 7.4, respectively), in comparison to M1 receptors in canine isolated saphenous vein (-log KB = 6.9) or M3 receptors in a range of guinea-pig isolated smooth muscles including ileum, trachea, fundus, seminal vesicle or oesophagus (-log KB = 6.6-6.8). In rat aorta, the -log KB value at the M3 receptor (5.9) was slightly, but significantly, lower. In competition radioligand binding studies, imperialine was also selective toward to M2 sites in rat myocardium (-log Ki = 7.2) with respect to M1 and M3 sites (rat cerebral cortex, rat submaxillary gland; -log Ki = 6.1 and 5.7, respectively). However, it did not significantly discriminate between rat cardiac M2 sites and putative M4 sites in rabbit lung (-log Ki = 6.9). Imperialine resembles the alkaloid himbacine in terms of its pharmacological profile at muscarinic receptor subtypes in that it acts as an M2 selective antagonist with respect to M1 or M3 sites. It may also provide a second, commercially available, antagonist with which to discriminate between M1 and M4 receptors.

Effects of vasoactive intestinal peptide, helodermin and galanin on responses of guinea-pig lung parenchyma to histamine, acetylcholine and leukotriene D4

1. The effect of vasoactive intestinal peptide (VIP) was studied on the contractile response of guinea-pig lung parenchymal strips (GPP) induced by bronchoconstrictor agonists, such as leukotriene D4 (LTD4), histamine and acetylcholine (ACh). This effect of VIP was compared with helodermin, a peptide that is structurally related to VIP, and galanin, another neuropeptide that is thought to co-exist with VIP. 2. VIP (10 nM) induced a potent and reversible inhibition of the contractions of GPP induced by LTD4 (1-30 pmol) but did not affect those due to ACh (1-100 nmol) or histamine (1-30 nmol). A ten fold higher concentration of VIP (100 nM) did not further inhibit LTD4-induced responses or reduce those induced by histamine or ACh. 3. Helodermin (10 nM) had a similar inhibitory effect on contractions of GPP induced by LTD4 (3-30 pmol) but did not affect contractions induced by histamine (1-10 nmol). 4. Indomethacin (2.8 microM) and salbutamol (10 nM) significantly reduced responses elicited by LTD4 and histamine but not those due to ACh. A ten fold higher concentration of salbutamol (100 nM) further inhibited the contractions due to LTD4 and histamine and at this concentration responses induced by ACh were inhibited. 5. VIP (10 nM) and helodermin (10 nM) significantly reduced the LTD4-induced release of thromboxane A2 (TXA2), measured as TxB2 by radioimmunoassay, from GPP. The smaller release of TxA2 induced by histamine was not significantly reduced in the presence of VIP. 6. In comparative studies, galanin (10-100 nM) did not affect contractions of GPP induced by either LTD4, histamine or ACh. In contrast to VIP and helodermin, both at 0.1-3 nmol, which induced doserelated relaxations of guinea-pig trachea, galanin was inactive on this preparation in doses of up to 3 nmol.7. In conclusion, our results show that contractions of GPP induced by LTD4 are more sensitive to inhibition by VIP and helodermin than are contractions due to histamine or ACh. This inhibition appears to be associated with the different contribution of released TxA2 to contractions evoked by the agonists. VIP and helodermin inhibit the cyclo-oxygenase-dependent component of the LTD4-induced response, as in the case of indomethacin.

Tracheal relaxing effects and beta 2-selectivity of TA-2005, a newly developed bronchodilating agent, in isolated guinea pig tissues

Tracheal relaxing effects and beta 2-selectivity of TA-2005 were investigated by functional experiments and radioligand binding assay in guinea pigs in comparison with those of other beta-agonists, isoproterenol, procaterol, formoterol and salbutamol. The relaxing activity of TA-2005 on histamine-induced contraction in the isolated trachea was most potent among the five agonists, and it was blocked by a beta 2-selective antagonist (ICI 118,551) but not by a beta 1-selective antagonist (bisoprolol). The potency of the relaxing effect was in the order of TA-2005 (pD2 = 9.79) greater than formoterol greater than procaterol greater than isoproterenol greater than or equal to salbutamol. The positive chronotropic effect of TA-2005 was similar to that of isoproterenol; and it was more potent than those of formoterol, procaterol and salbutamol in the isolated atria. The selectivity for tracheal muscle to atria of these agonists were in the order of procaterol greater than greater than or equal to formoterol greater than TA-2005 greater than salbutamol much greater than isoproterenol. A radioligand binding experiment using guinea pig lung and cardiac ventricle as beta 2- and beta 1-adrenoceptor sources, respectively, has also demonstrated that TA-2005 possesses extremely high affinity (IC50 = 1.04 nM) and selectivity (38-fold) to beta 2-adrenoceptors. By addition of GTP, the competition curve of [125I]iodocyanopindolol shifted rightward, indicating the agonist property. These results confirmed that TA-2005 is a highly beta 2-selective agonist that exerts a potent tracheal relaxing effect.

The influence of L-NG-nitro-arginine on field stimulation induced contractions and acetylcholine release in guinea pig isolated tracheal smooth muscle

The interaction between parasympathetic and inhibitory non-adrenergic, non-cholinergic nerves in tracheal smooth muscle was investigated by determining the effects of the NO-synthase inhibitor L-NG-nitro-arginine (L-NOARG) on contractions and the associated acetylcholine release elicited by field stimulation of the muscle. At frequencies above 2Hz contractile responses to field stimulation were potentiated by L-NOARG (50 microM). alpha-chymotrypsin pre-treatment potentiated contractile responses at all frequencies, but the effects of L-NOARG were unaltered. The effect of L-NOARG on responses to 5Hz electrical stimulation was not mimicked by D-NOARG, was reversed by L-, but not D-arginine and was unaffected by epithelium removal. L-NOARG did not affect responses to exogenous acetylcholine nor the overflow of 3H from tissues previously loaded with [3H]-choline. It is therefore concluded that field stimulation of tracheal smooth muscle induces the release of an endogenous nitrate, which, by an inhibitory action on smooth muscle, functionally antagonises the concomitantly released parasympathetic neurotransmitter.

Pharmacological analysis of agonist-antagonist interactions at acetylcholine muscarinic receptors in a new urinary bladder assay

1. Agonist-antagonist interactions at acetylcholine (ACh) muscarinic receptors have been analysed by use of an improved urinary bladder assay, isolated and intact, from the mouse. With 5-methylfurmethide as agonist, validated cumulative concentration-effect curves were obtained in less than 7 min by re-dosing before the response plateaux began to fade. 2. The pKB value estimated for pirenzepine was 6.76. The pKB values estimated for atropine and N-methylatropine from data obtained at concentrations which produced dose-ratios greater than 20 and 60 were 8.90 and 9.58, respectively. 3. The deviation from simple competitive behaviour at low dose-ratios with atropine and N-methylatropine was consistent with the operation of saturable antagonist removal processes. The deviation observed with atropine was corrected by pre-incubation with methylbutyrate, an alternative substrate for 'atropine esterase'. 4. The simple competitive behaviour of N-methylatropine was restored following pre-incubation with the neuronal choline uptake blocker hemicholinium-3 (HC-3). However, the pKB estimated for N-methylatropine under these conditions was low. This latter result could be accounted for by the observed behaviour of HC-3 as a competitive antagonist of ACh muscarinic receptors (pKB = 4.01). 5. We conclude that the modified mouse urinary bladder assay is suitable for the quantitative analysis of muscarinic receptor interactions. In addition, we postulate the existence of a previously undescribed uptake mechanism for quaternary muscarinic receptor antagonists.

Evidence that part of the NANC relaxant response of guinea-pig trachea to electrical field stimulation is mediated by nitric oxide

1. The nitric oxide (NO) synthesis inhibitors NG-monomethyl L-arginine (L-NMMA) and L-nitroarginine methyl ester (L-NAME) reduced relaxations of guinea-pig tracheal smooth muscle elicited by stimulation of intramural non-adrenergic, non-cholinergic (NANC) nerves, but D-NMMA had no effect. L-NAME was 10-30 times more potent than L-NMMA. Relaxations produced by sodium nitroprusside and vasoactive intestinal polypeptide (VIP) were not affected by L-NMMA or L-NAME. 2. The inhibitory effect of L-NMMA on NANC-mediated relaxations was partially reversed by L-arginine but was not affected by D-arginine. 3. VIP antibody and alpha-chymotrypsin abolished or greatly reduced the relaxant action of VIP and reduced relaxations elicited by stimulation of NANC nerves; the residual NANC relaxation was further reduced by L-NAME. 4. The results suggest that NO and VIP are mediators of NANC-induced relaxations of guinea-pig tracheal smooth muscle. We propose the term 'nitrergic' to describe transmission processes which are mediated by NO.

The role of the epithelium in modulating the responses of guinea-pig trachea induced by bradykinin in vitro

1. The effect of removing the epithelium on the responses of the guinea-pig isolated trachea (GPT) to bradykinin (BK) and prostaglandin E2 (PGE2) was investigated. 2. BK (3 pmol-10 nmol) induced dose-related relaxations of the intact (with epithelium), and contracted the rubbed (without epithelium) preparation of GPT. Similar responses were also obtained with PGE2 (0.3-3.0 nmol). 3. Indomethacin (1.4 microM) modified the BK-induced response of intact GPT, from a relaxation to a contraction, but inhibited the BK-induced contraction of the rubbed GPT. 4. There was a significant increase in PGE2 release from the intact GPT following stimulation with BK. 5. Removal of the epithelium from the GPT significantly reduced both basal and BK-induced generation of PGE2. 6. The induction of tone in the rubbed GPT by addition of acetylcholine (ACh) caused BK and PGE2 (0.3 nmol-3 nmol) to produce relaxations of the tissue. 7. Salbutamol (10(-8) M-10(-6) M) reduced the relaxations induced by BK on intact GPT, in a concentration-dependent manner. 8. These results suggest that both tone and an epithelial-dependent cyclo-oxygenase mechanism are important in modulating BK-induced responses of GPT.

Beta-adrenoceptor desensitization induced by antigen challenge in guinea-pig trachea

As beta-adrenoceptor function in the lung could be relevant in asthma, we carried out a functional and biochemical study of the possible occurrence of beta-receptor desensitization after the anaphylactic reaction induced in vitro in actively sensitized guinea-pig tracheas. The relaxing effect of epinephrine and vasoactive intestinal polypeptide (VIP) was tested in tracheal strips. Binding was studied with tracheal membranes and 125I-cyanopindolol. Antigen challenge resulted in a marked decrease of epinephrine-induced relaxation paralleled by a 50% reduction in beta-receptor number. The adrenergic system was specifically affected since VIP-induced relaxation was not modified by the anaphylactic reaction. In some experiments tissues were pretreated with hydrocortisone or indomethacin. Both these drugs prevented antigen exposure from impairing epinephrine relaxation, suggesting the involvement of eicosanoids in this phenomenon. Our data clearly indicate the occurrence of beta-receptor desensitization as a consequence of the anaphylactic reaction, thus impairment of the adrenergic system might play a role in asthma.

Effects of cularine and other isoquinoline alkaloids on guinea-pig trachea and human bronchus

The relaxant effects of the isoquinoline alkaloids, cularine, antioquine, obaberine and 6, 7-dimethoxy-1, 2, 3, 4-tetrahydroisoquinoline, with structures related to that of papaverine, have been studied on the guinea-pig isolated trachea and human bronchus against contractions induced by acetylcholine (ACh), histamine, neurokinin A (NKA) and KCl. These effects were compared with those of papaverine and theophylline. Among the alkaloids tested, the most potent was cularine, the relaxant activity of which, in terms of pD2, was between those of papaverine and theophylline. The results showed that for the guinea-pig isolated trachea and the human bronchus, the cularine concentrations required to inhibit K(+)-induced contractions were close to those necessary to counteract ACh-, histamine- and NKA-induced contractions. The relaxant activity of cularine was not modified when it was tested on tracheal preparations under resting tone or after epithelium removal. In addition, cularine was able to inhibit Ca2(+)-induced contractions in a Ca2(+)-free, K(+)-enriched solution at the same concentrations as those which inhibited the action of the different contractile agents in normal Krebs solution. All these data show that cularine displays non-specific antispasmogenic activity on guinea-pig and human airways. The lower relaxant activity (pD2) of cularine compared with papaverine suggests the importance of free rotation of the isoquinoline-benzyl ring linkage as well as of the degree of hydrogenation of the heterocyclic ring in the spasmolytic effects of isoquinoline compounds.

Peripheral type benzodiazepine receptors and response to adenosine on the guinea-pig isolated trachea

It has been reported that dipyridamole, an adenosine uptake inhibitor, and some benzodiazepines potentiate the responses to adenosine in peripheral organs and in particular, on guinea-pig isolated atria. In this paper, we have examined the potentiation of responses to adenosine produced by dipyridamole, diazepam and four compounds with selective agonistic activity towards the central (clonazepam) or peripheral (Ro5-4864) type benzodiazepine receptors or antagonistic activity towards the central (flumazenil) or peripheral (PK 11195) benzodiazepine receptors in guinea-pig trachea in vitro. In preparations under basal tone and in the absence of adenosine, dipyridamole (10(-5) M) and benzodiazepines (10(-4) M) with the exception of flumazenil induced a relaxation of the airway smooth muscle. In addition, diazepam (10(-4) M) attenuated the phasic response to histamine (10(-5) M). Dipyridamole, and the benzodiazepine agonists diazepam, Ro5-4864 and clonazepam (10(-5) to 10(-4) M) produced potentiation of the tracheal response to adenosine, the rank order of potency being dipyridamole (pKi = 7.77 +/- 0.12, n = 8) greater than Ro5-4864 (pKi = 5.43 +/- 0.18, n = 6) greater than or equal to diazepam greater than clonazepam (pKi = 4.84 +/- 0.11, n = 6). The two benzodiazepine receptor antagonists, flumazenil and PK 11195, gave a significant but small potentiation to adenosine only at 10(-4) M. In the presence of dipyridamole (10(-5) M), diazepam (10(-4) M) did not cause any further potentiation to adenosine. Additionally, the potentiation produced by diazepam was not antagonised by flumazenil, whereas it was potently antagonised by PK 11195. Similarly, PK 11195 potently inhibited the adenosine potentiation produced by Ro5-4864.(ABSTRACT TRUNCATED AT 250 WORDS)

Passive cigarette smoke exposure induces airway hyperreactivity to histamine but not to acetylcholine in guinea-pigs

We have investigated the changes in airway reactivity induced in guinea-pigs by passive cigarette smoke exposure. In particular, we studied the development of airway hyperresponsiveness both in vivo and in vitro after passive exposure of the animals to cigarette smoke in a plexiglass box. Passive smoke exposure significantly (p less than 0.01) increased histamine induced bronchoconstriction. The dose-ratio calculated between histamine dose-response curves constructed in control and smoke exposed animals was 2.13 (95% confidence limits: 1.46-3.09). Acetylcholine induced bronchoconstriction was not potentiated after the same smoke exposure, indicating some specificity of the mediators involved in the airway hyperresponsiveness triggered by passive smoke exposure. The airway hyperreactivity induced by smoke exposure was associated with a specific increase in histamine contraction induced in vitro in lung parenchymal strips but not in tracheae or pulmonary arteries. Maximal histamine contraction in parenchymal strips taken from smoke exposed animals was significantly (p less than 0.01) enhanced by approximately 110% when compared to control. There was a significant (p less than 0.01) increase in the number of macrophages and eosinophils in the bronchoalveolar lavage fluid of animals passively exposed to cigarette smoke, but no mucus hypersecretion was evident. Our data demonstrate the occurrence of airway hyperreactivity induced by passive cigarette smoke exposure, which involves increased smooth muscle reactivity and cell recruitment.

Beta-adrenoceptor reactivity after epithelium removal in guinea-pig trachea in vitro

In guinea-pig isolated tracheae precontracted with pilocarpine (2 x 10(-5)M) mechanical removal of the epithelium did not significantly modify the degree of relaxation induced by three different adrenergic agonists: epinephrine (adrenaline), isoproterenol (isoprenaline) and salbutamol. The failure of epithelium removal to modify isoproterenol relaxant activity was observed in both spontaneous tone and pilocarpine precontracted tracheae. In tracheae obtained from actively sensitized (ovalbumin) guinea-pigs, log-concentration response curves of epinephrine and salbutamol were unchanged by epithelium damage, whereas that of isoproterenol was slightly shifted to the left. In ovalbumin sensitized tracheae exposed to the antigen (ovalbumin, 50 micrograms/ml) epithelium removal enhanced the relaxant activity of the three adrenergic agonists used. Beta-adrenoceptor desensitization (isoproterenol, 10(-6)M for 20 min twice) carried out in ovalbumin actively sensitized tracheae with or without epithelium, shifted the log-concentration response curves of isoproterenol to a similar rightward position. The present data suggest that the airway epithelium plays a minor role in the regulation of guinea-pig tracheal sensitivity to beta-adrenoceptor agonists, which is evident only in a classical model of experimental asthma.

Characterization of the prostanoid receptor profile of enprostil and isomers in smooth muscle and platelets in vitro

1. Enprostil is composed, in approximately equal proportions, of 4 allenic isomers which are prostanoids structurally related to prostaglandin E2 (PGE2). The isomers are denoted as RS-86505-007, RS-86812-007 which are in the 'natural' R and S configuration (with respect to PGE2) and RS-86505-008 and RS-86812-008 which are in the 'unnatural' R and S configuration. In the present study we have characterized their activity at prostanoid receptors, in vitro. 2. Enprostil acted as a highly potent (-log EC50 = 8.30 +/- 0.08; mean +/- s.e.mean, n = 6) EP3 receptor agonist in the guinea-pig vas deferens, although no activity was observed at guinea-pig tracheal EP2 receptors at concentrations up to and including 10 microM. Attempts to study the action of enprostil at EP1 receptors were complicated by a general increase in the spontaneous activity of the guinea-pig isolated ileum. This response was stereospecific (i.e. observed, with the 'natural' R and S isomers only) and was not mediated through EP1, FP or TP receptors. 3. Enprostil also exhibited a potent agonist effect at FP and TP receptors in the rat colon and guinea-pig aorta (-log EC50 values = 7.34 +/- 0.11 and 6.54 +/- 0.07, mean +/- s.e. mean, n = 4-8 respectively). No activity at concentrations up to and including 10 microM was observed at DP or IP receptors in the guinea-pig platelet mediating inhibition of ADP-induced aggregation. 4. A similar profile was observed with the 'natural' R and S allenic isomers of enprostil (RS-86505- 007 and RS-86812-007, respectively); RS-86505-007 was between 4 and 10 fold more potent than the racemic enprostil. The 'unnatural' allenic R and S isomers of enprostil were much less potent than enprostil, with the latter being virtually inactive. 5. Enprostil and the 'natural' R and S isomers, therefore, were EP3, FP and TP agonists, being most potent at the EP3 receptor. The preferred configurations for these receptors appears to be the R, and to a lesser extent the S, form of the natural allenic isomer. The effect of enprostil at EP1 receptors was not characterized in view of the presence of excitatory EP3 receptors in the guineapig ileum. These data were in accordance with the pharmacological activity of enprostil, including inhibition of gastric acid secretion (possibly EP3) and diaorrhea (possibly TP).

The pharmacological properties of the peptide, endothelin

1. The effect of endothelin (ET-1) has been studied on isolated vascular and non-vascular preparations, using both functional and competition radioligand binding techniques. The effects of endothelin on blood pressure were studied in both anaesthetised, chemically denervated normotensive and spontaneously hypertensive rats (SHR). 2. Endothelin elicited contractile responses in the rat thoracic aorta, perfused mesenteric bed, rabbit mesenteric artery and portal vein. The maximal responses in the rat aorta were enhanced by removal of the endothelium, and were reduced in the presence of either a cyclo-oxygenase inhibitor (indomethacin) or a thromboxane receptor antagonist (SQ 29,548). In terms of potency, the most sensitive preparation was the rat endothelium-denuded aorta and rat perfused mesenteric bed (-log EC50 values = 8.2 +/- 0.07 and 8.2 +/- 0.12, mean +/- s.e.mean, n = 4, respectively). In the perfused mesenteric bed of the rat the maximum response to endothelin (219 +/- 12 mmHg, n = 4) was greater than that to either phenylephrine (maximal response = 67 +/- 9 mmHg; n = 4) or KCl (maximal response = 110 +/- 6 mmHg, n = 4). 3. Endothelin elicited contractile responses of the guinea-pig isolated ileum, oesophageal muscularis mucosae and uterus. Responses were also observed in the rat fundic strip and paced left atria. The guinea-pig urinary bladder, trachea, rat vas deferens and anococcygeus exhibited little or no response to endothelin at the concentrations studied (1 x 10(-12)-3.2 x 10(-8) M). Of the above preparations, the ileum and oesophageal muscularis mucosae were the most sensitive to endothelin (-log EC50 = 8.5 +/- 0.11 and 8.4 +/- 0.06, n = 6, respectively), exhibiting potencies similar to those observed in the endothelium-denuded aorta of the rat. 4. In competition-radioligand binding studies, endothelin did not displace either [3H]-PN 210-100 or [125I]-(-)-omega-conotoxin GVIA from binding sites in membranes from rat cerebral cortex and, skeletal muscle or from guinea-pig cerebral cortex and hippocampus, respectively. This indicates a lack of direct interaction of endothelin at the dihydropyridine binding site and the N-type calcium channel, respectively. However, in functional studies, contractile responses to endothelin (1 x 10(-8) M) in the endothelium-denuded aorta of the rat were potently reversed by nifedipine, verapamil, and prenylamine (-log IC50 values = 8.0 +/- 0.13, 7.2 +/- 0.09 and 6.6 +/- 0.08, n = 4-8, respectively). In addition, the responses to endothelin were virtually abolished in the presence of Krebs physiological salt solution containing no calcium but with 1 x 10-M EDTA added. Preequilibration with either (-)-w-conotoxin (1 x 10-6M) or tetrodotoxin (1 x 10-6M) did not affect responses to endothelin. 5. In chemically denervated rats, endothelin (1pmolkg-'-10nmolkg- , i.v.) exhibited pressor responses, which were unaffected by a 3 h pretreatment with indomethacin. In the SHR, the effects on blood pressure were not significantly different from those observed in normotensive animals at any of the doses studied. A transient (duration < 30 s) depressor response was also observed in all groups studied at a dose of 0.1-1 nmol kg-1 i.v. 6. In conclusion, endothelin is a potent contractile agonist in both vascular and non-vascular muscle. It appears to elicit responses partly via the entry of extracellular calcium (by a mechanism distinct from that of other calcium facilitators) and partly by release of endoperoxides.

RS-61756-007: a potent and selective thromboxane receptor (TP) agonist

The activity of RS-61756-007 (methyl-9-oxo, 15 alpha-hydroxy, 16-phenoxy, 17,18,19,20-tetranor prosta 4,5, 13(E) trienoate, 4,5,6(R), 8(R)) has been assessed at prostanoid receptors (DP, EP1, EP2, FP, IP and TP) in-vitro. The activity profile of RS-61756-007 resembles that of U46619, in that agonism was observed at TP and to a lesser extent at FP receptors, but there was no activity at the remaining subtypes. The actions of both RS-61756-007 and U46619 were antagonized in a similar manner by the TP antagonist SQ 29,548. We conclude that RS-61756-007 is a highly potent TP agonist.

Active sensitisation modifies beta-adrenoceptor reactivity in guinea-pig trachea

The occurrence of beta-adrenoceptor desensitisation in clinical experience, after long term therapy with specific beta 2-agonists, is still an open question, even if this phenomenon is easily observed in different experimental models. Since the majority of these experiments have been performed in normal animals, we investigated the possible occurrence of beta-adrenoceptor desensitisation in the ovalbumin actively sensitised guinea-pig model of experimental asthma. The isoproterenol concentration-response curves performed in pilocarpine contracted guinea-pig trachea in vitro were shifted to the right by the beta-adrenoceptor desensitisation procedure, which was achieved by the in vitro administration of isoproterenol (10(-5) M x 2 times x 20 min each) both in normal and ovalbumin sensitised tissues. The same desensitisation procedure markedly affected epinephrine-relaxing capacity in both normal and ovalbumin actively sensitised guinea-pig tracheae. However, the ovalbumin sensitised tissue seemed to be more sensitive than normal to the specific beta 2-agonist procaterol; in parallel the beta 2-mediated relaxation was more impaired by isoproterenol-induced beta-adrenoceptor down regulation in ovalbumin sensitised trachea when compared to normal. Similar results have been obtained using salbutamol as the beta 2-adrenoceptor desensitising agent. The changes in beta-adrenoceptor reactivity between normal and ovalbumin sensitised guinea-pig tracheae seemed to depend on the active sensitisation process. No difference in the degree of beta-adrenoceptor down regulation was observed in passively ovalbumin sensitised guinea-pig trachea as compared to normal. These data suggest that, in this model of experimental asthma, beta-adrenoceptor reactivity is in some way modified and that this phenomenon might contribute to the genesis of asthma.

Problems associated with the application of the Cheng-Prusoff relationship to estimate atropine affinity constants using functional tissue responses

We have studied problems associated with the application of the Cheng-Prusoff relationship to the estimation of atropine dissociation constants from isolated guinea-pig tracheal responses. The values obtained have been compared to dissociation constants derived using Schild analysis. It was observed that when either carbachol (an agonist of high efficacy) or pilocarpine (an agonist of low efficacy) was used the dissociation constants estimated for atropine using the Schild analysis were very similar to those estimated using the Cheng-Prusoff relationship. In these latter experiments the agonist concentration used was the EC80. When the agonist concentration used was increased to supramaximal concentrations (3-fold greater than the EC100) the dissociation constants derived were overestimations by approximately 10-fold. It is concluded that in certain circumstances the results obtained using both the Cheng-Prusoff relationship and Schild analysis are comparable. However, it is unlikely that the Cheng-Prusoff relationship is generally applicable and that Schild analysis is clearly preferable in determining antagonist dissociation constants.

The interaction of methoctramine and himbacine at atrial, smooth muscle and endothelial muscarinic receptors in vitro

1. The action of methoctramine and himbacine at muscarinic receptors has been studied using guinea-pig isolated trachea, oesophageal muscularis mucosae, paced left atria, and rat aortic preparations. 2. Methoctramine (1 x 10(-6)-3.2 x 10(-4) M), but not himbacine, elicited positive inotropic responses. These responses were enhanced by pretreating the animals with reserpine. The responses in reserpine-treated animals were not antagonized by phentolamine (1 x 10(-6) M) but were antagonized by propranolol (1 x 10(-6) M). 3. Methoctramine, but not himbacine, exhibited allosteric inhibitory effects at cardiac muscarinic receptors, resulting in a curvilinear Schild plot. Deviations from competitive antagonism were also observed in combination dose-ratio experiments using atropine and methoctramine. At 1 x 10(-6) M, the pKB value for methoctramine was 7.88 +/- 0.15 (mean +/- s.e.mean, n = 5). The pA2 value for himbacine at cardiac muscarinic receptors was 8.52 +/- 0.06 (n = 3). 4. At tracheal and oesophageal muscularis mucosal smooth muscle receptors, the Schild plots for both antagonists were linear. The pA2 values for methoctramine at receptors in these two preparations were similar (6.08 +/- 0.05 and 6.03 +/- 0.09 respectively, n = 4) and were approximately 60 fold less than those values observed at atrial receptors. Himbacine, also exhibited similar values at muscarinic receptors in the trachea and oesophageal muscularis mucosae (7.61 +/- 0.05 and 7.57 +/- 0.04 respectively, n = 4). 5. Muscarinic receptors mediating relaxation of the rat aortic endothelium exhibited pA2 values for methoctramine (5.87 +/- 0.12, n = 6) which were similar to those observed in the smooth muscle, but not the atria. The pA2 values for himbacine at endothelial muscarinic receptors were approximately 0.5 pA2 units lower than those observed at muscarinic receptors in smooth muscle (6.92 + 0.80, n = 6). In addition, the Schild slopes for methoctramine and himbacine at these receptors were significantly (P < 0.05) less than unity. 6. Methoctramine, and to a lesser extent himbacine, are potent and selective antagonists for cardiac muscarinic receptors. However, caution should be used in interpretation of the data with methoctramine in view of the inhibitory allosteric properties and direct inotropic actions of this compound.