Tracheal Smooth Muscle

Modulatory role of endogenous androgens on airway smooth muscle tone in isolated guinea-pig and bovine trachea; involvement of beta2-adrenoceptors, the polyamine system and external calcium

Androgens relax several smooth muscles, including the airways. They also contract ileum and myocardium via nongenomic mechanisms. To find out whether androgens modulate airway smooth muscles in different species and further assess their mechanism of action, regarding the role of beta-adrenoceptors, polyamines and extracellular Ca(2+), and the modulation of contraction, 5 alpha-dihydrotestosterone, testosterone and 5 beta-dihydrotestosterone were used. A preliminary study was performed to evaluate the effect of 5 alpha-dihydrotestosterone, a non-aromatisable derivate of testosterone, in isolated guinea-pig trachea and a more exhaustive characterisation was followed in bovine trachea, to also characterise the effect of testosterone and 5 beta-dihydrotestosterone. The androgens elicited a nongenomic epithelium-independent relaxation of the trachea which had been precontracted. In the bovine trachea, the order of potency was: testosterone>5 alpha-dihydrotestosterone=5 beta-dihydrotestosterone. This effect was inversely proportional to the magnitude of carbachol-raised tone and was independent of beta(2)-adrenoceptors, since the beta-blockers, propranolol and ICI-118,551, and beta(2)-adrenoceptor desensitisation did not modify 5 alpha-dihydrotestosterone-elicited relaxation. 5 alpha-Dihydrotestosterone was unable to displace the radiolabel, [(3)H]dihydroalprenolol, from these receptors in the binding assay. Polyamine synthesis was not involved in this androgen effect, since an ornithine decarboxylase inhibitor, alpha-difluoromethylornithine, was ineffective. The androgens were more effective relaxing bovine trachea precontracted by KCl (80 mM), suggesting a calcium entry blockade, as reported for several smooth muscles. This mechanism might be involved in the observed 5 alpha-dihydrotestosterone facilitation of salbutamol-relaxation. Androgens facilitated carbachol-elicited contraction independently of polyamine synthesis, contrary to what has been reported in the ileum. Therefore, androgens modulate tracheal smooth muscle tone which might be of importance in the regulation of airway reactivity.

The action of the peptidoleukotriene LTD4 on intracellular calcium in rat mesangial cells

The dose-dependent effect of CGP 45715A on the LTD4-induced Ca2+ response of glomerular mesangial cells has been studied. Our results demonstrate that the LTD4-dependent increase in the cytosolic Ca2+ concentration primarily involves an InsP3-mediated release of Ca2+ from intracellular storage sites and to a minor extent an enhanced influx of Ca2+ through receptor-operated Ca2+ channels located in the plasma membrane. The action of CGP 45715A on the Ca2+ response is an inhibitory one and is convincingly explained by a displacement of LTD4 from its receptor site(s). The contractile effect of LTD4 on pulmonary smooth muscle is proposed to be mainly caused by a receptor-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate.

An isometric method to study respiratory smooth muscle responses in mice

An isometric method to measure the smooth muscle tone of murine tracheas in vitro was developed. Nine trachea rings from just beneath the larynx were prepared free of excess tissue with the help of a binocular microscope. These trachea parts were slipped onto supports in an organ bath containing Krebs' solution. Isometric tension was measured with a force displacement transducer connected to the upper-trachea support, and is expressed as changes in grams force. The cholinergic agonist carbachol contracted isolated tracheas. Serotonin also induced contractions, but was less potent than carbachol. Histamine induced tracheal contractions only at very high concentrations. Sympathomimetic beta adrenergic agonists relaxed carbachol-precontracted tracheas with the following order of potency: isoprenaline (beta 1 and beta 2 adrenoceptor agonist) greater than salbutamol (beta 2 adrenoceptor agonist) greater than prenalterol (beta 1 adrenoceptor agonist). Adrenaline and noradrenaline relaxed carbachol-precontracted tracheas, with adrenaline being the more potent relaxant. For the study of airway reactivity, this mouse trachea model has several advantages over immunopharmacologic models: The immune system of the mouse has been characterized extensively, and many reagents are available to study the immune system and, thus, possible interactions of this system with pharmacological mechanisms. Other animal models used in pharmacology are generally less well defined immunologically.