Influence of the epithelium on responsiveness of guinea-pig isolated trachea to contractile and relaxant agonists (original) (raw)
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Influence of epithelium on beta-adrenoceptor desensitization of guinea pig tracheal smooth muscle
The effect of tissue incubation with a 2-agonist of denuded and intact epithelium trachea on the responsiveness to isoprenaline and-receptor blocked by propranolol (CR-1) was examined in this study. We examined the effect of epithelium removal on the-adrenoceptor desensitization resulting from incubation of guinea pig trachea in the-adrenergic agonist isoprenaline (10 M). Desensitization was measured as the change in EC 50 , the concentration of-agonist that produced 50% relaxation of tracheal rings contracted with methacholine. As a second measure of desensitization, we measured the shift in EC 50 resulting from incubation of tracheal rings with the-adrenoceptor antagonist propranolol (20 nM), expressed as CR-1 ([post-propranolol EC 50 /baseline EC 50 ] − 1). Initially, we measured desensitization immediately after incubation in isoprenaline; subsequently, we repeated the protocol and allowed a 30 min rest between the end of incubation and the measurement. The sensitivity of denuded epithelium trachea to isoprenaline and (CR-1) was significantly higher than that of intact epithelium only in non-incubated preparations (p < 0.05 to p < 0.001). Incubation to isoprenaline caused a significant reduction in the tracheal response to isoprenaline in both the denuded groups (p < 0.005 for both cases) and intact epithelium groups (p < 0.05 for both cases). Incubation to isoprenaline also caused a significant reduction in (CR-1) value in both the denuded groups (p < 0.005 for group 2 and p < 0.001 for group 4) and intact epithelium only in group 1 (p < 0.05). However, the changes in EC 50 due to tissue incubation with isoprenaline were significantly greater in denuded than intact epithelium trachea (p < 0.05 for all cases) and for CR-1 value only in groups 1 and 2 (p < 0.05). These results indicate decrease in both tracheal response to-agonist (tolerance) and CR-1 (due to incubation of tissues with isoprenaline), which were greater in denuded epithelium groups.
British Journal of Pharmacology, 1990
A method has been used in guinea-pig isolated tracheal rings to achieve selective drug entry from the adventitial or mucosal surface. A study has been made of the effects of epithelium removal on responses to spasmogens entering the tissue solely from the adventitial or the mucosal surface. 2 Cumulative concentration-response curves for KCl (1 to 100mM), acetylcholine (0.1 uM to 10mM) and histamine (1 UM to mM) were constructed in intact and epithelium-denuded tracheal rings in circumstances where drug entry was unrestricted or restricted to the adventitial or mucosal surface. 3 Epithelium removal did not alter the responsiveness or sensitivity of tracheal rings to KCl either when drug entry was unrestricted or when drug entry was restricted to the adventitial or mucosal surface. 4 When acetylcholine entered from the mucosal or adventitial surfaces of intact tracheal rings its concentration-response curve was displaced to the right with respect to that obtained for unrestricted drug entry. A greater rightward shift was observed for mucosal drug entry than for adventitial drug entry. Epithelium removal potentiated acetylcholine entering from the mucosal surface to a greater extent (27.5 fold) than it potentiated acetylcholine entering from both surfaces (4 fold). Epithelium removal did not potentiate effects of acetylcholine entering from the adventitial surface alone. 5 In intact tracheal segments, concentration-response curves for histamine entering from the mucosal surface were displaced to the right compared with those for histamine entering in an unrestricted fashion or from the adventitial surface alone. This displacement was absent in epithelium-denuded preparations. Epithelium removal potentiated (2-3 fold) histamine entering from the mucosal surface or entering in an unrestricted way. It did not potentiate histamine entering from the adventitial surface alone. 6 Our findings suggest that the epithelium does not modulate tracheal responses to KC1. Its ability to modulate responses to acetylcholine and histamine is observed when these spasmogens enter the tissue from the mucosal surface but not when they enter from the adventitial surface. The mechanism by which epithelium removal preferentially potentiates acetylcholine and histamine entering from the mucosal rather than the adventitial surface remains to be determined.
European Journal of Pharmacology, 1990
Guinea-pig tracheas were perfused with recirculating modified Krebs-Wenseleit solution while monitoring changes in ~flow-o~t~ow pressure difference, which is an index of trachealis muscle tone. The reactivities of the trachealis muscle to methacholine, histamine and isoproterenol applied separately to the mucosal (intraluminal, IL) or serosal (extralvminal, EL) compartments were compared, and evidence for the agonist-induced release of epithelium-derived &axing factor (EpDRF) was sought. All agents were more potent when added to the EL compartment, but the IL/EL EC, ratios were different: 100 for methacho~ne, 41 for ~sta~ne and 25 for isoproterenol. Methacho~ne or histamine added to the IL compartment, after the preparations were pre-contracted with the same concentration of the agonist or 30 mM KC1 added EL, did not result in relaxation. Likewise, IL isoproterenol did not evoke contraction. IL KC1 evoked relaxation. The results indicate that the epithelium reduces access of bronchoactive agents to the muscle, while an i~ediate relaxant effect of EpDRF released by agonists couid not be demonstrated. Trachea; Epithelium; EpDRF (epithelium-delved relaxing factor); Smooth muscle (airway); (Reactivity) 0014-2999/90/$03.50 (23 1990 Elsevier Science Publishers B.V. (Biomedical Division)
β-Adrenoceptor desensitization in guinea-pig isolated trachea
European Journal of Pharmacology, 1988
Exposure to (-)-isoprenaline (25 /~M, 1 h) caused a stereoselective, time and concentration-related decrease in smooth muscle flz-adrenoceptor function in guinea-pig trachea. Furthermore, tracheal relaxant responsiveness to the fl-adrenoceptor agonists (_+)-fenoterol and (-)-noradrenaline was reduced, while that to theophylline and nitroprusside was unaffected. Responsiveness to forskolin was marginally but significantly reduced. Indomethacin, a cyclooxygenase inhibitor and mepacrine, an inhibitor of phospholipid turnover, had no significant effect on the extent of isoprenaline-induced desensitization. Conversely, cortisol (25 #M) significantly reduced desensitization and enhanced the rate of spontaneous recovery of responsiveness to isoprenaline. Desensitization was not accompanied by a reduction in the density of fl-adrenoceptors in the trachea, as assessed by binding and light microscopic autoradiography using [125I]iodocyanopindolol ([125I]CYP). Thus, desensitization was probably caused primarily by fl-adrenoceptor/adenyl cyclase uncoupling. This model may be useful in investigations of the effect of glucocorticoids on the fl-adrenoceptor dysfunction recognized in severe asthma.
Evidence for Non-adrenergic Non-cholinergic Contractile Responses in Bovine and Swine Trachea
Pulmonary Pharmacology & Therapeutics, 1997
Non-adrenergic non-cholinergic (NANC) contraction of airway smooth muscle has been observed in some but not all animal species. The aim of this study was to investigate the NANC-contractile responses in bovine and swine trachea. Proximal and distal bovine and swine trachea were cut in strips and placed in 10 ml organ baths equilibrated in Krebs Henseleit (KH) solution and electrically stimulated (10 sec, 60 V, 2 ms, 4, 10 and 30 Hz). Contractile frequency response curves performed in the presence of the muscarinic antagonist, atropine (100 mM), the angiotensin converting enzyme inhibitor, captopril (1 M) and the neutral endopeptidase inhibitor, thiorphan (1 M), added 30 min prior to electrical field stimulation (EFS). In some tissues, incubated with atropine thiorphan and captopril, were also evaluated the effects of a pretreatment with capsaicin (10 M) or a selective NK 1 receptor antagonist, SR 14033 (100 nM) added to the baths 30 min prior to EFS. Bovine and swine proximal and distal tracheal preparations contracted in a frequency-dependent manner to EFS (4, 10 and 30 Hz). Some experiments were also performed with substance P (0.1nM to 1 M) in absence or in presence of SR 14033 (10 nM or 100 nM). At the maximum frequency tested (30 Hz), the contractile response elicited in bovine proximal and distal preparations was 194.5±17.1% and 229.7±24.1%, of ACh (100 M), respectively. Similarly, the contractile response elicited by EFS (30 Hz) in swine proximal and distal preparations was 187.2±12.1% and 181.6±9.2% of ACh (100 M), respectively. In tissues incubated with atropine, a significant decrease in smooth muscle sensitivity to EFS was observed (P<0.05). When tissues were pretreated with captopril and thiorphan, a significant increase in the contractile response to EFS (30 Hz) was observed in all tested tissue preparations (bovine, proximal 210.1±14.4%, distal 264.3±16.2%; swine, proximal 199.3±14.9%, distal 206.3±16.2%, P<0.05). In the presence of atropine, captopril and thiorphan a significant increase in the contractile response was observed in bovine and swine distal preparations compared with tissues incubated with atropine only (P<0.05). These effects were antagonized by a pretreatment with a selective NK 1 receptor antagonist, SR 14033. A pretreatment with capsaicin statistically (P<0.05) enhanced EFS-induced contraction in all tested preparations respect to tissues incubated with atropine, thiorphan and captopril. Substance P induced a concentration dependent contraction of bovine and swine isolated tracheal preparations which was antagonized by a pretreatment with a selective NK 1 receptor antagonist, SR 14033. No significant difference in the contractile potency (EC 50 ) nor in maximum response (Emax) was observed to exogenously administered substance P between proximal and distal tracheal preparations. These data suggest that NANC contractile responses are present in bovine and swine trachea and are more evident in distal airways.
BETA1- and BETA3-ADRENOCEPTORS Mediate Relaxation in Ovine Trachealis Smooth Muscle
Journal of Autonomic Pharmacology, 1999
1 Isoprenaline (non-selective) and noradrenaline (b 1 -selective) concentration-dependently relaxed ovine tracheal strips precontracted with carbachol. The pD 2 values were 7.07 0.08 and 6.13 0.10 for isoprenaline and noradrenaline, respectively. In the same preparation, salbutamol either produced weak relaxation or in some cases, contractile responses indicating the presence of very little or no b 2 -adrenoceptors in this preparation. 2 Isoprenaline-and noradrenaline-induced relaxations were antagonized by propranolol and atenolol with pA 2 values in the range reported in the literature for an action on b 1 -adrenoceptors. ICI 118551 also antagonized isoprenaline-and noradrenaline-induced relaxation but at concentrations much higher than are required to block b 2 -adrenoceptors, confirming that b 2adrenoceptors do not contribute significantly to these responses. 3 The selective b 3 -adrenoceptor agonist, BRL 37344A produced concentration-dependent relaxation of tracheal strips. BRL 37344A was a full agonist producing 100% relaxation of carbacholinduced tone. BRL 37344A-induced relaxation was weakly antagonized by propranolol confirming an action, mainly, on b 3 -adrenoceptors. Cyanopindolol antagonized isoprenaline-induced relaxation (in the presence of propranolol, 10 ±7 M) with a pA 2 value of 8.06 0.24. 4 It was therefore concluded that b 1 -and b 3 -adrenoceptors mediated agonist-induced relaxation in sheep tracheal strips.
Interaction between β1 and β2 adrenoceptors in the isolated guinea-Pig trachea
Pharmacological Research Communications, 1979
The presence of 81 and B 2 adrenoceptors is demonstrated in the guinea-piq tracheal smooth muscle and both receptors subserve the same function. The functional relationship between the two 8-receptors in the guinea-pi~ trachea, which is difficult to explain, is discussed in relation to the capacity of 81 receptors to take over their function, if the 82 receptors are completely blocked.
Phenylethylamine effects on histamine-induced contraction of isolated guinea-pig trachea rings
Jugoslovenska medicinska biohemija, 2005
Histamine produces constriction of tracheal smooth muscle via H1 receptors, but it also decreases tracheal smooth muscle tone via H2 and H3 receptors. In addition, it has already been reported that phenylethylamine is competitive antagonist of histamine N-methyl-transferase (HMT), enzyme responsible for rapid inactivation of histamine. Our results suggest possibility that phenylethylamine as competitive antagonist of histamine N-methyl-transferase leads to potentiation of histamine induced constriction of isolated guinea-pig trachea, which could be consequence of decreased histamine methylation and subsequent histamine inactivation. At the same time, phenylethylamine had no direct effect on basal tone of intact isolated trachea rings, as well as on other mechanisms leading to increased responsiveness of guinea-pig tracheal smooth muscle (acetylcholine, KCl, electro stimulation).
British Journal of Pharmacology, 1993
A method is described whereby either the serosal (Out) or epithelial (In) sides of rat isolated tracheae were selectively perfused. Perfusion with BRL 38227 (10-8-5 x 10-6 M; In/Out) of preparations with intact epithelium (+ EP) precontracted with carbachol (10-6 M; Out/In) produced complete relaxation. Perfusion with aminophylline (10-5-10-3 M; In) of + EP preparations precontracted with carbachol (10-6 m; Out) also produced complete relaxation. 2 In preparations precontracted with carbachol (10-6 M) epithelium removal (-EP) increased the sensitivity to the relaxant effect of BRL 38227 (In), but not BRL 38227 (Out) [log EC50, + EP/-EP; carbachol (In), BRL 38227 (Out): 6.76 ± 0.11 vs 6.67 ± 0.15; carbachol (Out), BRL 38227 (In): 5.93 ± 0.06 vs 6.25 ± 0.07]. Removal of the epithelium increased also the sensitivity to BRL 38227 (In) of preparations precontracted with a lower concentration (5 x 10' M) of carbachol (Out). [-log EC50, + EP/-EP, carbachol (Out), BRL 38227 (In): 6.19 ± 0.14 vs 6.58 ± 0.17]. 3 Removal of the epithelium did not affect the sensitivity to BRL 38227 (In) of preparations precontracted with a higher concentration (5 x 10-6 M) of carbachol (Out). 4 In both + EP and-EP preparations precontracted with carbachol (10-6 M; Out), BRL 38227 (In) had a more potent relaxant effect than aminophylline (In) (EC., BRL 38227 vs aminophylline, + EP/-EP: 5.93 ± 0.06 vs 3.66 ± 0.11/6.25 ± 0.07 vs 3.77 ± 0.11). 5 In preparations precontracted with carbachol (10-6 M; Out), removal of the epithelium did not affect the sensitivity to aminophylline (In) but increased the degree of precontraction (Tm,,) following epithelial but not serosal stimulation with carbachol. 6 We conclude that BRL 38227, a K+ channel activator, is a potent relaxant of rat tracheal smooth muscle precontracted with carbachol, and that the effect can be partially inhibited by the presence of an intact tracheal epithelium, whereas the relaxant effect of aminophylline is not.