Intensity of swimming exercise influences tracheal reactivity in rats

Abstract

Studies that evaluate the mechanisms for increased airway responsiveness are very sparse, although there are reports of exercise-induced bronchospasm. Therefore, we have evaluated the tracheal reactivity and the rate of lipid peroxidation after different intensities of swimming exercise in rats. Thus, male Wistar rats (age 8 weeks; 250-300 g) underwent a forced swimming exercise for 1h whilst carrying attached loads of 3, 4, 5, 6 and 8% of their body weight (groups G3, G4, G5, G6 and G8, respectively; n=5 each). Immediately after the test, the trachea of each rat was removed and suspended in an organ bath to evaluate contractile and relaxant responses. The rate of lipid peroxidation was estimated by measuring malondialdehyde levels. According to a one-way ANOVA, all trained groups showed a significant decrease in the relaxation induced by aminophylline (10(-12)-10(-1) M) (pD2=3.1, 3.2, 3.3, 3.3 and 3.2, respectively for G3, G4, G5, G6 and G8) compared to the control group (pD2=4.6) and the Emax values of G5, G6, G8 groups were reduced by 94.2, 88.0 and 77.0%, respectively. Additionally, all trained groups showed a significant increase in contraction induced by carbachol (10(-9)-10 (-3) M) (pD2=6.0, 6.5, 6.5, 7.2 and 7.3, respectively for G3, G4, G5, G6 and G8) compared to the control group (pD2=5.7). Lipid peroxidation levels of G3, G4 and G5 were similar in both the trachea and lung, however G6 and G8 presented an increased peroxidation in the trachea. In conclusion, a single bout of swimming exercise acutely altered tracheal responsiveness in an intensity-related manner and the elevation in lipid peroxidation indicates a degree of oxidative stress involvement.

Fig. 1.

Lactate production as a function of exercise intensity. Data are reported as means ± SEM (n = 5 per group). G3, G4, G5, G6 and G8: exercise intensity based on loading with 3, 4, 5, 6 and 8% of body weight, respectively, during swimming exercise. *P<0.05 vs. control; ^#P<0.05 vs. G3; ^†P<0.05 vs. G4; ^‡P<0.05 vs. G5; ^¥P<0.05 vs. G6. (one-way ANOVA test).

Fig. 2.

Representative traces and relaxant effect on rat trachea induced by aminophylline in control, G3, G4 and G5 (A and B, lower intensities), and G6 and G8 (C e D, higher intensities) groups. Data are reported as means ± SEM (n=5 per group). G3, G4, G5, G6 and G8: exercise intensity based on loading with 3, 4, 5, 6 and 8% of body weight, respectively, during swimming exercise. *P<0.05 vs. control (one-way ANOVA test). CCh: carbachol; AA: arachidonic acid; W: wash.

Fig. 3.

Representative traces and contractile effect on rat trachea induced by CCh in control, G3, G4 and G5 (A and B, lower intensities), and G6 and G8 (C e D, higher intensities) groups. Data are reported as the means ± SEM (n = 5 per group). G3, G4, G5, G6 and G8: exercise intensity based on loading with 3, 4, 5, 6 and 8% of body weight, respectively, during swimming exercise. *P<0.05 vs. control; ^#P<0.05 vs. G3 (one-way ANOVA test). CCh: carbachol.

Fig. 4.

Levels of lipid peroxidation in trachea (A) and lung (B) in control, G3, G4, G5, G6 and G8 groups. Data are reported as means ± SEM (n=5 per group). G3, G4, G5, G6 and G8: exercise intensity based on loading with 3, 4, 5, 6 and 8% of body weight, respectively, during swimming exercise. *P< 0.05 vs. control; ^#P<0.05 vs. G4; ^†P<0.05 vs. G5; ^‡P<0.05 vs. G6 (one-way ANOVA test).