Preparation of bovine tracheal smooth muscle for in vitro pharmacological studies

Sex hormones modulate salbutamol-elicited long-term relaxation in isolated bovine tracheal strips

Sex hormones are of interest regarding gender differences in the clinical manifestations of airway diseases. No conclusive data are available on the sex hormone modulation of β-adrenoceptor-mediated responses on airways. To this aim, isolated preparations of bovine trachea were used to establish the sex hormone influence on salbutamol-elicited relaxation. This had 2 components, a full acute relaxation followed by a loss of efficacy, close to half of the effect. The remaining half was reverted by the β-blocker, propranolol. The loss of salbutamol-elicited relaxation might reflect the receptor desensitization, as shown by the lack of effect by subsequent administration of salbutamol, and the decrease in the immunostaining of β(2)-adrenoceptors. Sex hormones differently modified the salbutamol-elicited response. Testosterone, but not other androgens or estradiol, had a synergic effect, facilitating the acute relaxation and decreasing the loss of spasmolytic effect, associated with an increase in the latency of desensitization and a decrease in the time taken to reach long-term steady-state tone. These effects, not modified by the antiandrogen flutamide or epithelium removal, seem to be independent of a modulation of β(2)-adrenoceptor desensitization. Testosterone also relaxed preparations with desensitized β-adrenoceptor. Therefore, testosterone modulates tracheal smooth muscle tone, facilitating bronchodilation caused by β(2)-adrenoceptor agonists which might be of pharmacological interest.

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.