Estudo das alterações da contratilidade de anéis de traquéia isolada de ratos em resposta ao carbacol e ao potássio após treinamento físico

Abstract

This work aimed to determine the contractility of tracheal smooth muscle of rats submitted to short-term light exercise, trained for 1h or pre-trained and, then, trained for 1, 5 and 10hs (PT1, PT5 and PT10, respectively), as well as, animals sensitized with OVA, submitted to exercise for 5hs and subsequently challenged, with the objective of verifying the changes caused by exercise in this muscle, also determining the interference of antigen bronchoprovocation on the contractility of tracheal smooth muscle of animals previously exercised. To conduct the study male rats (250-350g) were subjected to different protocols of swimming, by 1, 5 and 10hs, in addition to one group that was subjected to sensitization with OVA and 21 days later, challenged at intervals of 30 min through sensitizing antigen inhalation (group S/D). In the sensitized group submitted to exercise, this latter was held for 5 days before OVA challenge (group S/E pre-challenge). The animals were sacrificed 15 min after the swimming session or 24 hs after antigen challenge, in the case of rats submitted to asthma model. Sedentary rats were not subjected to any training session. Asthma control group inhaled only the vehicle (NaCl 0.9%). For in vitro experiments the trachea was removed and mounted in an isolated organ bath containing 5ml of Tyrode solution (maintained at 37 ± 0.5 °C) and aerated with O2. Concentration-effect curves (CEC) were designed for carbachol and potassium chloride. The results showed that the pD2 values were not significant among the groups except in PT5 and PT10, both in relation to group PT1. The maximum response values were significantly increased and higher in the groups PT1 (107,62 ± 3,57), PT5 (116,35 ± 0,54) and PT10 (123,50 ± 2,59) compared to the sedentary group (82.70 ± 5,90), when carbachol was used as the contractile stimulus. A similar situation occurred in the groups PT1 (105,19 ± 1,12), PT5 (112,02 ± 1,44) and PT10 (119,56 ± 0,95) as compared to the sedentary group (90,45 ± 2,22), for potassium and S/D (100,74 ± 4,79) and S/E pre-challenge groups (109,09 ± 3,68) as compared to the sensibilized group (82,69 ± 5,90) for carbachol, as well as, S/D (105,50 ± 2,37) and S/E pre-challenge (115,05 ± 1,96) groups when compared to the sensibilized one for potassium (93,11 ± 3,58). To verify the involvement of nitric oxide, acetylcholine, and oxidative stress on the pro-contractile mechanism of the tracheal smooth muscle induced by exercise, nitrite levels, acetylcholinesterase (AChE) activity and thiobarbituric acid reactive species (TBARS), as a way of determining lipid peroxidation, were determined. Nitrite levels decreased in the PT5 group as compared to sedentary and 1h trained groups. In the animals subjected to the asthma protocol there was a significant decrease in the nitrite levels in the S/D and S/E prechallenge groups. An increase in lipid peroxidation occurred in the groups PT1, PT5 and PT10 in relation to the sedentary one. In the asthmatic group, the TBARS values were significantly higher in S/D and S/E pre-challenge groups as compared to the control one. The AChE activity showed a significant reduction in the groups PT1, PT5 and PT10 in relation to sedentary and 1h trained groups. The groups S/D and S/E pre-challenge also presented a decrease on AChE activity. Therefore, the results showed that short-term light exercise increases the tracheal smooth muscle contractility of the study groups, probably with the participation of nitric oxide, acetylcholine, and lipid peroxidation in this pro-contractile mechanism.