Ventilation distribution during histamine provocation

Insulin NO-dependent action on airways smooth muscles

In order to find out how insulin acts on airway smooth muscle and which mechanisms could be involved, we studied the effect of insulin on contraction induced, first, by KCl and, second, by Acetylcholine (Ach), before and after epithelium removal, and finally in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor. Tracheal smooth muscle strips from 24 rabbits, 6 being used for each experiment. Each muscle strip was pretreated with a solution containing either 80 mM KCl or 10(-5) Ach and increasing doses of insulin (range 10(-10)--10(-5) M) in the presence or absence of 10(-4) M L-NAME. A reference curve for contraction evoked by 80 mM KCl or 10(-5) M Ach in the presence or absence of 10(-4) M L-NAME was recorded each time before the pretreatment mentioned above. Insulin evoked a concentration-dependent inhibition of tracheal smooth muscle contraction, induced by 80 mM KCl or 10(-5) M Ach. After epithelium removal, insulin (10(-8), 10(-7) M) evoked statistically significant increases to the contractions induced by 10(-5) M Ach compared to the contractions induced by 10(-5) M Ach and insulin in the presence of epithelium (P < 0.05). These increases were higher when 10(-4) M l-NAME was added to the bath (P < 0.05). In conclusion, these results indicate that insulin inhibits tracheal smooth muscle contraction by acting on epithelium and releasing NO.

Effects of endothelin-1 on KCl-induced contractions of airway smooth muscles

The objective of the study was to investigate the effect of endothelin-1 (ET-1) on KCl-induced contractions. Tracheal strips were obtained from 12 male rabbits, perfused with Krebs solution and aerated continuously by bubbling with a mixture of 95% O(2)-5% CO(2). Increasing concentrations of ET-1 (10(-12)-10(-7) M) additionally to KCl caused more contractions than KCl-induced (P<0.05). A total of 10(-7) M ET-1-induced 14.56% more contraction. Methylene blue (10(-5) M) decreased all the contractions induced from simultaneous use of KCl and ET-1. Methylene blue caused about 18% relaxation of contraction induced from KCl (80 mM) and ET-1 (10(-8) M). Consequently ET-1 increases the KCl-induced contractions of airway smooth muscles. This effect seem to mediate by a nitric oxide (NO)-guanylate cyclase-cGMP pathway, in which methylene blue is inactivator of guanylate cyclase.

Airway responsiveness: role of inflammation, epithelium damage and smooth muscle tension

The purpose of this study was the effect of epithelium damage on mechanical responses of airway smooth muscles under different resting tension. We performed acetylcholine (ACh) (10(-5) M)-induced contraction on tracheal strips from 30 rabbits in five groups (0.5, 1, 1.5, 2 and 2.5 g) before and after epithelium removal. At low resting tension (0.5-1.5 g), the epithelium removal decreased the ACh-induced contractions. At 2 g resting tension, the epithelium removal increased the ACh-induced contractions of airways with intact epithelium about 20%. At 2.5 g resting tension, the elevation of contraction is about 25% (P<0.01). Consequently, after epithelium loss, the resting tension determines the airway smooth muscles responsiveness. In asthma, mediators such as ACh act on already contracted inflammatory airways, which results in additional increase of contraction. In contrast, low resting tension, a condition that simulates normal tidal breathing, protects from bronchoconstriction even when the epithelium is damaged.