J.M.H. Preuss

Relationship between endothelin-1 binding site densities and constrictor activities in human and animal airway smooth muscle.

1 Endothelin‐1 (ET‐1) binding site densities and constrictor activities were compared in airway smooth muscle preparations of human, guinea‐pig, rat and mouse. 2 The mean contractile response to 0.3 μm ET‐1 (measured as the % maximum response to 10 μm carbachol, % Cmax ± s.e.mean) and the mean concentration of ET‐1 producing 30% (95% confidence limits) were respectively; 85.9 ± 5.4% and 3.4nm (2.4–5.0) for mouse trachea (n = 11), 88.8 ± 4.7% and 18.2 nm (11.2–25.2) for rat trachea (n = 6), 71.0 ± 7.1% and 35.2 nm (5.4–231) for human bronchus (n = 3), and 32.3 ± 3.0% and 241 nm (125–460) for guinea‐pig trachea (n = 6). 3 Light microscopic autoradiography revealed specific [125I]‐ET‐1 binding sites localized to the smooth muscle band, with very low levels of binding associated with cartilage, submucosal and epithelial cells. 4 Quantitative autoradiographic analyses of the concentration‐dependence of specific [125I]‐ET‐1 binding (0.1–2nm) to smooth muscle revealed similar dissociation constants but markedly different specific binding site densities for the various animal species. The order of densities of specific [125I]‐ET‐1 binding sites was rat trachea (69.0 ± 11.2 amol mm−2) > human bronchus (42.7 ± 17.5 amol mm−2) > mouse trachea (28.7 ± 2.6 amol mm−2) > guinea‐pig trachea (8.3 ± 1.8 amol mm−2). 5 A positive relationship between [125I]‐ET‐l binding site density and ET‐1 constrictor activity was observed in airway smooth muscle preparations from rat, human and guinea‐pig. The greater sensitivity of mouse trachea to the constrictor actions of ET‐1 was not dependent on the release of cyclo‐oxygenaseor epithelium‐derived constrictor substances, but may have been due to an inter‐species difference in the receptor‐effector system for ET‐1.

The role of story‐telling in organizational leadership

The importance of story‐telling in organizational life has often been overlooked in contemporary organizational and leadership literature. Throughout history, leaders ‐ political and religious ‐ have used story‐telling as a powerful motivational tool, particularly during times of uncertainty, change and upheaval or in response to crises. This article looks at the role of story‐telling as an integral part of the human experience and at its applications in modern organizational life. The article concludes by suggesting that the art of story‐telling is still, despite recent advances in communication technologies, an essential managerial skill ‐ particularly for leaders of organizations.

Endothelin‐1‐induced [3H]‐inositol phosphate accumulation in rat trachea

1 The effects of endothelin‐1 (ET‐1) and of the muscarinic cholinoceptor agonist, carbachol, on [3H]‐inositol phosphate ([3H]‐InsP) accumulation and smooth muscle contraction were determined in rat isolated tracheal tissue. 2 ET‐1 (1 μm) and carbachol (10 μm) induced significant accumulation of [3H]‐InsPs in myo‐[2‐3H]‐inositol‐loaded rat tracheal segments. Several components of the tracheal wall including the airway smooth muscle band, the cartilaginous region and the intercartilaginous region generated significant levels of [3H]‐InsPs in response to ET‐1 and carbachol. Following stimulation with ET‐1, a greater proportion of tracheal [3H]‐InsPs were generated in the intercartilaginous region (49%) than in either the airway smooth muscle band (25%) or cartilaginous region (26%). However, when the respective weights of these regions is taken into account, ET‐1‐induced accumulation of [3H]‐InsPs was greatest in the airway smooth muscle band. The tracheal epithelium did not appear to generate [3H]‐InsPs in response to ET‐1 or modulate either basal or ET‐1‐induced accumulation of [3H]‐InsPs in rat tracheal segments. 3 In the rat tracheal smooth muscle band, ET‐1 caused a time‐ and concentration‐dependent accumulation of [3H]‐InsPs. Concentrations of ET‐1 as low as 10 nm produced significant accumulation of [3H]‐InsPs (1.23 ± 0.10 fold increase above basal levels of 295 ± 2 d.p.m. mg−1 wet wt., n = 3 experiments). At 10 μm, the highest concentration used, ET‐1 produced similar levels of [3H]‐InsP accumulation (7.03 ± 0.55 fold above basal levels, n = 5) to that produced by a maximally effective concentration of carbachol (10 mm; 7.97 ± 0.31 fold increase above basal levels, n = 4). ET‐1‐induced accumulation of [3H]‐InsPs was not significantly affected by indomethacin (5 μm), nordihydroguaiaretic acid (NDGA, 10 μm), WEB 2086 (10 μm) or phosphoramidon (10 μm). 4 ET‐1 also produced concentration‐dependent contractions of epithelium‐denuded rat tracheal ring preparations. The mean concentration of ET‐1 producing 50% of the maximum contractile response to carbachol (EC50) was 31 nm (95% confidence limits, 20–49 nm, n = 12). The presence of an intact tracheal epithelium, indomethacin (5 μm), WEB 2086 (10 μm) and phosphoramidon (10 μm) had no significant effect on the mean EC50 for ET‐1‐induced contraction (n = 5). In contrast, NDGA (10 μm) inhibited ET‐1‐induced contractions (4.0 fold increase in mean EC50, P > 0.001, n = 5). However, this effect of NDGA did not appear to be related to inhibition of leukotriene synthesis via lipoxygenase since the leukotriene antagonist SKF 104353 did not affect ET‐1‐induced contractions (n = 5) and moreover, leukotriene C4 and leukotriene D4 did not contract rat isolated tracheal smooth muscle preparations (n = 4). 5 The threshold concentrations of ET‐1 that produced increases in smooth muscle contraction and [3H]‐InsPs accumulation were similar, although the EC50 for [3H]‐InsP accumulation was 2.9 fold greater than that for smooth muscle contraction. For carbachol, the EC50 for [3H]‐InsP accumulation (mean EC50 = 5.0 μm, 1.2–21 μm, n = 4) was 25 fold greater than that for smooth muscle contraction (mean EC50 = 0.20 μm, 0.17–0.24 μm, n = 12). 6 It seems likely that ET‐1 has a direct effect on InsP generation in rat tracheal smooth muscle and that this is largely responsible for the spasmogenic actions of this peptide.

Epithelium-derived inhibitory factor in human brochus

The potencies of histamine and methacholine were significantly increased by approximately 2- and 5-fold respectively in human non-diseased isolated bronchi on removal of the epithelium. In contrast, no increases in spasmogen potency were observed following epithelium removal in bronchi obtained from a sample of asthmatic human lung. The failure of epithelium removal to increase asthmatic bronchial sensitivity to histamine may have been due to a reduction in the release of an epithelium-derived inhibitory factor (EpDIF) resulting from disease-induced epithelial damage. A co-axial bioassay system in which endothelium-denuded rat aorta was used as the assay tissue was used to detect the release of a vasorelaxant EpDIF from human bronchial tissue. Histamine (100 microM) and methacholine (25 microM), in the presence of indomethacin (5 microM), reduced phenylephrine-induced tone in endothelium-denuded rat aorta in co-axial assemblies by 75 +/- 11 and 67 +/- 9% respectively. Removal of the bronchial epithelium abolished these responses, indicating that they were mediated by an EpDIF. It is possible that human airway smooth muscle is sensitive to this vasorelaxant EpDIF and that the absence of the source of this factor following epithelium removal caused the increases in sensitivity to spasmogens. Alternatively, the human bronchial epithelium may also release an EpDIF selective for airway smooth muscle.

Epithelial modulation of the relaxant activity of atriopeptides in rat and guinea-pig tracheal smooth muscle

Three peptide components of atrial natriuretic factor (ANF) caused relaxation of carbachol-contracted guinea-pig isolated tracheal smooth muscle. These were the 1-28, 5-28 and 5-27 peptide sequences (ANF(1-28), ANF-(5-28) and ANF-(5-27)). The peptides were 10-30 times more potent in epithelium-denuded than in epithelium-intact preparations. In the absence of airway epithelium, ANF-(1-28) was the most potent relaxant (mean pD2 = 7.40 +/- 0.08), with ANF-(5-27) and ANF-(5-28) 2-3 fold less potent. The neutral endopeptidase inhibitor phosphoramidon (1 microM) increased the potency of ANF-(5-27) in both epithelium-intact and epithelium-denuded guinea-pig tracheal rings. In contrast, removal of the epithelium from rat trachea, or pretreatment with phosphoramidon (1 microM) decreased relaxant responsiveness to ANF-(5-27). Thus, in rat trachea, epithelial endopeptidase may convert ANF-(5-27) to a more active relaxant peptide. Human bronchial preparations with or without epithelium, obtained from non-diseased lung samples and from a single sample of asthmatic lung, were virtually unresponsive to ANF-(5-27). Consistent with the spasmolytic effects of ANF in guinea-pig trachea, autoradiographic analysis revealed the presence of a sparse population of specific binding sites for [125I]ANF-(1-28) over both tracheal smooth muscle and epithelium. The present study shows that the relaxant effects of atriopeptins in rat and guinea-pig airway smooth muscle were modulated by the epithelium and the activity of neutral endopeptidase. However, marked species differences in airway smooth muscle responsiveness to ANF and in the modulatory role of the airway epithelium were evident.

Evidence that epithelium‐dependent relaxation of vascular smooth muscle detected by co‐axial bioassays is not attributable to hypoxia

1 The present study was undertaken to examine further the contribution of hypoxia to airway epithelium‐dependent relaxation of rat aorta in the co‐axial bioassay. 2 Endothelium‐denuded rat aorta contracted with phenylephrine (0.05 μm) relaxed in a time‐dependent manner (t½ = 8.3 ± 0.4 min, n = 38) when the bathing solution was bubbled with 95% N2 and 5% CO2. In co‐axial bioassays, the t½ for histamine (100 μm; guinea‐pig trachea)‐ and methacholine (100 μm; rabbit bronchus)‐ induced relaxation was 1.9 ± 0.2 min (n = 14) and 1.2 ± 0.1 min (n = 26), respectively. 3 Hypoxia‐induced relaxation was not associated with a rise in intracellular guanosine 3′:5′‐cyclic monophosphate (cyclic GMP). This contrasts with previous findings of an elevation in cyclic GMP associated with epithelium‐dependent relaxation of rat aorta in co‐axial bioassays. 4 Hypoxia‐induced vascular relaxation was antagonized by the ATP‐sensitive K+ channel blocker, glibenclamide (100 μm). In contrast, glibenclamide (100 μm) failed to inhibit histamine (100 μm; guinea‐pig trachea)‐ and methacholine (0.1–100 μm; rabbit bronchus)‐induced release of epithelium‐derived inhibitory factor (EpDIF), in co‐axial bioassays. Glibenclamide (100 μm) antagonized BRL 38227 (lemakalin), but not isoprenaline‐induced relaxation of phenylephrine‐contracted rat aorta. 5 These data strongly suggest that the airway epithelium‐dependent relaxant responses observed in co‐axial bioassays cannot be attributed to hypoxia.

Muscarinic cholinoceptor subtypes mediating tracheal smooth muscle contraction and inositol phosphate generation in guinea pig and rat

The effects of the muscarinic cholinoceptor antagonists atropine (non-selective), pirenzepine (M1-selective), methoctramine (M2-selective) and 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP; M3-selective) were examined on the responsiveness of guinea pig and rat tracheal tissue to acetylcholine and carbachol. Results indicate that smooth muscle contraction in isolated tracheal tissue from both species was mediated primarily by muscarinic M3 cholinoceptors. The effects of atropine, pirenzepine and 4-DAMP were similar against the contractile actions of acetylcholine and carbachol in both species and in epithelium-intact and epithelium-denuded tissue. In contrast, differences in the effects of methoctramine in antagonising contractile responses to acetylcholine and carbachol were observed between the two species and following epithelium removal in the guinea pig. Thus, whilst this study has found that tracheal smooth muscle contraction in the guinea pig and rat is mediated primarily by muscarinic M3 cholinoceptors, anomalies in the functional inositol phosphate generation results obtained with the muscarinic cholinoceptor antagonists highlight species differences in the actions of acetylcholine and carbachol in eliciting smooth muscle contraction suggesting the possible existence of functional non-M3 muscarinic cholinoceptors.

The influence of age on isolated tracheal responsiveness to spasmogens

The influence of animal age was examined on the responses of guinea-pig (birth-156 weeks) and rat (4-136 weeks) isolated tracheal tissue to the spasmogens histamine, 5-hydroxytryptamine (5-HT) and potassium ions (K+) using functional and biochemical techniques. Over the ages birth-12 weeks in the guinea-pig, K+ potency decreased 1.5 fold whereas histamine potency increased 2-fold between the ages of birth-2 weeks and then declined to original levels by age 20 weeks. 5-HT potency declined over the entire age range examined, resulting in a 25.1 fold decrease between the ages of 1 and 156 weeks. In the rat, 5-HT potency remained unchanged and a small but progressive increase in K+ potency was observed with respect to animal age. Significant age-related changes in inositol phosphate accumulation were observed in both unstimulated and histamine-stimulated isolated guinea-pig tracheal smooth muscle which did not correlate with the functional changes observed in response to spasmogenic stimulation. The results describe disparate age-related changes between two species of different spasmogenic agonists with the majority of age-related changes occurring during the maturation phase of growth of the guinea-pig.

Influence of age on epithelium-dependent responsiveness of guinea-pig and rat tracheal smooth muscle to spasmogens

The current study describes the influence of age and the presence of the epithelium on guinea-pig and rat tracheal airway smooth muscle sensitivity to the spasmogens histamine, acetylcholine, carbachol and potassium. In guinea-pig trachea from animals aged 2-52 weeks the potency of each of these spasmogens decreased with increased animal age. In contrast, no age-dependent changes in the potency of acetylcholine, carbachol or potassium were seen in rat trachea. Removal of the tracheal epithelium was associated with significant increases in the potencies of histamine and acetylcholine in guinea-pig trachea and of acetylcholine in rat trachea, but not of carbachol or potassium in either species. For histamine in guinea-pig trachea, the largest potency increase (4.6-fold) occurred in tissue from 6-week-old animals, with the smallest increases in tissue from the youngest (2 weeks) and the oldest (52 weeks) animals. Thus, although the sensitivity of airway smooth muscle to this spasmogen fell between 2 and 12 weeks of age, the effect of epithelial removal on sensitivity to histamine was apparently increased during this period. Further studies are required to assess the reasons for increased histamine and acetylcholine potency in airway smooth muscle after epithelial ablation.

Age and region-dependent contraction to α-adrenoceptor agonists in rat and guinea-pig isolated trachea

The influence of age and of region on α‐adrenoceptor‐mediated contraction to (−)‐adrenaline and (−)‐noradrenaline was examined in rat (4–136 weeks) and guinea‐pig (2–156 weeks) isolated tracheal ring preparations with particular emphasis on the early (up to 12 weeks) maturation phase. In rat tracheal rings, significant regional variation was observed with respect to maximal (−)‐adrenaline‐induced contraction, such that the greatest activity was seen in ring preparations from the laryngeal end of the trachea. Tracheal rings from the carinal end responded very poorly or were unresponsive to (−)‐adrenaline, depending on animal age. These regional differences were seen across the age range. The potencies of (−)‐adrenaline and (−)‐noradrenaline remained unchanged with respect to animal age, but the maximum contractile tension that developed in response to these agonists increased with increasing animal age in all regions of the trachea. In guinea‐pig isolated tracheal tissue, maximum contractile responses (Emax) to (−)‐adrenaline and (−)‐noradrenaline remained unchanged with increasing animal age. In addition, there was no evidence for a region‐dependence in the responsiveness of tracheal tissue to α‐adrenoceptor‐mediated contraction in this species. In both guinea‐pig and rat isolated tracheal tissue, α‐adrenoceptor‐mediated contraction appeared to involve the activation of α1‐adrenoceptors.