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Physiology and Pharmacology of Temperature Regulation

Central angiotensin AT₁-receptor blockade affects thermoregulation and running performance in rats

Department of Physiology and Biophysics, Institute of Biological Sciences, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil

Submitted 16 January 2006 ; accepted in final form 5 April 2006

The effect of central angiotensin AT₁-receptor blockade on thermoregulation in rats during exercise on a treadmill (18 m/min, 5% inclination) was investigated. Core (T_b) and skin tail temperatures were measured in rats while they were exercising until fatigue after injection of 2 µl of losartan (Los; 20 nmol, n = 4; 30 nmol, n = 4; 60 nmol, n = 7), an angiotensin II AT₁-receptor antagonist, or 2 µl of 0.15 mol/l NaCl (Sal; n = 15) into the right lateral cerebral ventricle. Body heat rate (BHR), heat storage rate, threshold T_b for tail vasodilation (TT_bV), time to fatigue, and workload were calculated. During exercise, the BHR and heat storage rate of Los-treated animals were, respectively, 40 and 53% higher (P < 0.01) than in Sal-treated animals. Additionally, rats injected with Los showed an increased TT_bV (38.59 ± 0.19°C for Los vs. 38.12 ± 0.1°C for Sal, P < 0.02), a higher T_b at fatigue point (39.07 ± 0.14°C Los vs. 38.66 ± 0.07°C Sal, P < 0.01), and a reduced running performance (27.29 ± 4.48 min Los vs. 52.47 ± 6.67 min Sal, P < 0.01), which was closely related to the increased BHR. Our data suggest that AT₁-receptor blockade attenuates heat dissipation during exercise due to the higher TT_bV, leading to a faster exercise-induced increase in T_b, thus decreasing running performance.

tail vasodilation; fatigue; heat balance

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