Abstract
To assess the role of nitric oxide (NO) in central thermoregulatory mechanisms during exercise, 1.43 μmol (2 μL) of N ω-nitro- l-arginine methyl ester ( l-NAME, n = 6), a NO synthase inhibitor, or 2 μL of 0.15 M NaCl (SAL, n = 6) was injected into the lateral cerebral ventricle of male Wistar rats immediately before the animals started running (18 m min −1, 5% inclination). Core ( T b) and skin tail ( T tail) temperatures were measured. Body heating rate (BHR), threshold T b for tail vasodilation (TTbV), and workload ( W) were calculated. During the first 11 min of exercise, there was a greater increase in T b in the l-NAME group than in the SAL group (BRH = 0.17 ± 0.02 °C min −1, l-NAME, versus 0.09 ± 0.01 °C min −1, SAL, p < 0.05). Following the first 11 min until ∼40 min of exercise, T b levels remained stable in both groups, but levels remained higher in the l-NAME group than in the SAL group (39.16 ± 0.04 °C, l-NAME, versus 38.33 ± 0.02 °C, SAL, p < 0.01). However, exercise went on to induce an additional rise in T b in the SAL group prior to fatigue. These results suggest that the reduced W observed in l-NAME-treated rats (10.8 ± 2.0 kg m, l-NAME, versus 25.0 ± 2.1 kg m, SAL, p < 0.01) was related to the increased BHR in l-NAME-treated animals observed during the first 11 min of exercise ( r = 0.74, p < 0.01) due to the change in TTbV (39.12 ± 0.24 °C, l-NAME, versus 38.27 ± 0.10 °C, SAL, p < 0.05). Finally, our data suggest that the central nitric oxide pathway modulates mechanisms of heat dissipation during exercise through an inhibitory mechanism.
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