Abstract
The effect of central angiotensin AT1 receptor blockade on thermoregulation in rats (n=6) during exercise in treadmill (18 m.min−1, 5% inclination) was investigated. Core (Tb) and skin tail (Ttail) temperatures were measured in rats while they were exercising until fatigue after injection of 60 nmol of Losartan (2μL, angiotensin II AT1 receptor antagonist) or 0.15 M NaCl (2μL, SAL) into the right lateral cerebral ventricle. Heat storage (HS), threshold Tb for tail vasodilation (TTbV), and workload (W) were calculated. During the first 12 minutes of exercise, the body heating rate remained similar in both groups (0.05±0.02 °C/min, Losartan vs 0.04±0.02 °C/min, SAL). Following the first 12 minutes of exercise, Tb for control animals stabilized at 38.2±0.03 °C while Losartan animals showed a futher rise in Tb stabilizing at 38.4±0.07 °C. HS and TTbV were higher in the Losartan group than in the SAL group (HS = 163.4±36.6 cal, Losartan vs 100.6±47.0 cal, SAL; TTbV = 38.1±0.2 °C, Losartan vs 37.8±0.2 °C, SAL, p<0.05). Despite the greater heat storage, the Losartan rats showed a similar workload compared with SAL treated group (9.8±7.6 kgm, Losartan vs 10.8±7.9 kgm, SAL). Our data suggest that AT1 receptor blockade attenuates heat dissipation during exercise that leads to a faster exercise-induced increase in Tb during the steady state period. Supported by: CNPq, FAPEMIG, and CAPES.
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