Strapková A

Competition of NO synthases and arginase in the airways hyperreactivity.

The competition between arginases and NO synthases (NOS) for their common substrate L-arginine can be important in the airways hyperreactivity. We investigated the effect of the simultaneous modulation of arginase and NOS activities in allergen-induced airways hyperreactivity. We analysed the response of tracheal and lung tissue smooth muscle to histamine or acetylcholine after administration N(ω)-nitro-L-arginine methyl ester (L-NAME), aminoguanidine (AG) and N(ω)-hydroxy-L-arginine (NOHA) in the combinations in in vitro conditions. The results show the decrease of ovalbumin-induced hyperreactivity after inhibition of arginase activity with NOHA. A supplementation of L-arginine caused favourable effect on the airway smooth muscle response. We found the airway reactivity decrease on the whole if we used the combination of NOS and arginase inhibitors. The inhibition of both types of enzymes caused more expressive effect in tracheal smooth muscles. We recorded the difference in the response to histamine or acetylcholine. The simultaneous inhibition of iNOS (with AG) and arginase (with NOHA) evoked the most expressive effect. Results show the importance of competition of both types enzymes - NOS and arginase for the balance of theirs activities in the control of airways bronchomotoric tone in the conditions of the airways hyperreactivity.

Study of the interaction of glutamatergic and nitrergic signalling in conditions of the experimental airways hyperreactivity

BACKGROUND Glutamatergic and nitrergic system participate in the control of respiratory system functions. It is only little information regarding a possible interaction of both systems in the airways hyperractivity. We investigated the effect of agents modulating the activity of these systems on the experimental ovalbumin-induced airways hyperreactivity as well as on the changes of exhaled nitric oxide (eNO) levels. METHODS We used the agonists of NMDA receptors - N-methyl-D-aspartic acid (NMDA) and monosodium glutamate (MSG), selective competitive antagonist (DL-2-amino-5-phosphonovaleric acid - AP-5) and selective non-competitive antagonist (dizocilpine - MK-801) of these receptors. We used also non-specific inhibitor of NO synthases N(ω)-nitro-L-arginine methyl ester (L-NAME). The airways responsiveness to histamine or acetylcholine was evaluated under in vitro conditions. RESULTS NMDA administration caused the increase of tracheal smooth muscle response in ovalbumin-induced hyperreactivity to acetylcholine. The effect of MSG was less pronounced. MK-801 as well as AP-5 provoked the decrease of reactivity mainly to acetylcholine in tracheal smooth muscle. We recorded the changes in eNO levels. The activation of NMDA receptor with NMDA or MSG increased eNO levels. The inhibition of NO synthase with L-NAME caused the fall of eNO levels. MK-801 shows (within the group) the more expressive effect in the eNO levels during sensitization than AP-5 group. CONCLUSION The results confirm the possibility of NMDA receptors participation in the experimental airways hyperreactivity.

Glutamate receptors and the airways hyperreactivity.

It is proposed the link between the hyperactivity of NMDA receptors and airway hyperresponsiveness. We investigated the effect of agents modulating the activity of NMDA receptors in the ovalbumin-induced airway hyperreactivity in guinea pigs. The airways hyperreactivity was influenced by the agonist (NMDA) and selective antagonist - competitive (AP-5) and non-competitive (MK-801) of NMDA receptors. Airway responsiveness to histamine or acetylcholine was evaluated in in vitro conditions. NMDA administration caused the increase of tracheal smooth muscle response in ovalbumin-induced hyperreactivity to acetylcholine. MK 801 as well as AP-5 provoked the decrease of reactivity mainly to acetylcholine in tracheal smooth muscle, while the former, non-competitive antagonist was more effective. We recorded more pronounced response in tracheal than in lung tissue smooth muscle with more considerable response to acetylcholine than to histamine. The results of experiments show the modification of airway smooth muscles responses by agents modulating the activity of NMDA receptors. They confirm the possibility of NMDA receptors participation in experimental airway hyperreactivity. The results enlarge information regarding the link of the inflammatory diseases and glutamatergic system.

The influence of L-NAME on iNOS expression and markers of oxidative stress in allergen-induced airway hyperreactivity.

Nitric oxide (NO) effects in airways are influenced by the activity of NO-synthase isoforms and NO metabolism. Inducible NO-synthase (iNOS), which produces large amounts of NO, is active during the inflammatory process. NO quickly reacts, producing reactive oxygen species (ROS). In this study we attempted to detect the expression of iNOS and markers of ROS in the airway hyperreactivity (AHR) condition. The study was performed in guinea pigs, divided into four groups. Two groups were treated with the non-selective inhibitor of NO-synthase L-NAME. The other two groups were used as controls. Exhaled NO was monitored in vivo, AHR was assessed both in vivo and in vitro, and the expression of iNOS in lung homogenate, and oxidative stress markers were measured in the venous blood. L-NAME significantly affected the AHR only in in vitro condition, blocked the expression of iNOS in control but not in sensitized animals, and decreased the level of exhaled NO. The results concerning the oxidative stress markers are equivocal. The study confirmed that NO is involved in the regulation of AHR; the effects being mediated via iNOS and ROS activity.

Pharmacologic modulation of experimentally induced allergic asthma.

Pharmacologic modulation of experimentally induced allergic asthma Allergic asthma is the most frequent disease of the respiratory tract. The aim of the current experimental and clinical studies was to find new sources of drugs able to control asthmatic inflammation and airway hyperresponsiveness. Our experimental studies were focused on efficiency evaluation of substances able to influence activities of ion channels, phosphodiesterase (PDE) isoforms, substances from the group of polyphenols and NO metabolism modulators during experimentally induced allergic asthma.

L-Arginine Supplementation and Experimental Airway Hyperreactivity

The interest in L-arginine metabolism was triggered primarily by the discovery of nitric oxide (NO) synthesis in mammals and its remarkable biological roles. The real role of L-arginine in the airway hyperreactivity (AHR) has not been established yet. Therefore, we studied whether supplementation of L-arginine can influence the experimental AHR evoked by two different triggers - allergen and exogenous irritant (toluene vapours). Male TRIK strain guinea pigs were used in the study. We used two patterns of pretreatment with L-arginine in vivo, short- and long-term, in a dose of 300 mg/kg administered i.p., after which we studied reactivity of airway smooth muscles in vitro. Pretreatment with L-arginine for 3 days decreased the airway smooth muscle reactivity induced by toluene vapour, whereas pretreatment for 17 days was without any additional effect on smooth muscle reactivity. The short-term pretreatment in ovalbumin-induced hyperreactivity caused an increase in airway smooth muscle reactivity to lower concentrations of both bronchoconstrictors. On the other side, this pretreatment significantly decreased smooth muscle reactivity to high concentrations of both bronchoconstrictors. Supplementation of L-arginine resulted in a modification of the airway smooth muscle response. The effect of supplementation was different depending on the AHR trigger, airway region and pretreatment duration. The results also underscore the importance of an optimal L-arginine level for the control of bronchial tone.

Exogenous irritant-induced airway hyperreactivity and inhibition of soluble guanylyl cyclase.

The majority of nitric oxide (NO) effects in the respiratory system are caused by stimulation of soluble guanylyl cyclase (sGC) with subsequent increase of cyclic guanosine monophosphate (cGMP) production. The importance of this mechanism of NO action in airway hyperreactivity (AHR) pathogenesis is unknown. Therefore, the aim of our experiment was to examine the changes of airway reactivity enhanced by toluene vapor exposure in the presence or inhibition of sGC activity in guinea pigs. Animals were treated with a nonspecific sGC inhibitor, methylene blue, in a dose of 50 or 100 mg/kg body weight, administered by intraperitoneal injection 30 min before or after exposure to toluene vapors. The toluene exposure lasted 2 hr in each of 3 consecutive days under in vivo conditions. Thereafter, the tracheal and lung tissue smooth muscle response to cumulative doses of mediators (histamine or acetylcholine) was recorded under in vitro conditions. The exposure to toluene vapors significantly increased the airway reactivity to both mediators in comparison with the healthy animal group. The administration of methylene blue decreased the amplitude of airway smooth muscle contraction in toluene-induced hyperreactivity. The decreases were dependent on the inhibitor doses, on a regimen of administration (before or after toluene inhalation), the level of the respiratory system (trachea, lung), and the bronchoconstrictor mediators. Our results suggest that the interaction between NO and sGC may be important for airway reactivity changes, but other mechanisms of NO action are important in AHR pathogenesis, too.

Mucolytics and antioxidant activity

We investigated effects of the mucolytics ambroxol and N-acetylcysteine on airways reactivity evoked by histamine in guinea pigs exposed to toluene vapors. We did not find significant changes in reactivity of tracheal smooth muscle from animals treated with mucolytics compared to the control group. However, the administration of ambroxol and N-acetylcysteine caused a significant decrease in lung tissue reactivity. The effect of ambroxol was more pronounced after intraperitoneal injection than after inhalation, while N-acetylcysteine was only effective after inhalation. The protective effects of mucolytics in the lung tissue may be due to their antioxidant activity together with other mechanisms.