Central angiotensin A[T.sub.1]-receptor blockade affects thermoregulation and running performance in rats

The effect of central angiotensin A[T.sub.1]-receptor blockade on thermoregulation in rats during exercise on a treadmill (18 m/min, 5% inclination) was investigated. Core ([T.sub.b]) and skin tail temperatures were measured in rats while they were exercising until fatigue after injection of 2 [micro]l of losartan (Los; 20 nmol, n = 4; 30 nmol, n = 4; 60 nmol, n = 7), an angiotensin II A[T.sub.1]-receptor antagonist, or 2 [micro]l of 0.15 mol/l NaCl (Sal; n = 15) into the right lateral cerebral ventricle. Body heat rate (BHR), heat storage rate, threshold [T.sub.b] for tail vasodilation (T[T.sub.b]V), 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 T[T.sub.b]V (38.59 [+ or -] 0.19[degrees]C for Los vs. 38.12 [+ or -] 0.1[degrees]C for Sal, P < 0.02), a higher [T.sub.b] at fatigue point (39.07 [+ or -] 0.14[degrees]C Los vs. 38.66 [+ or -] 0.07[degrees]C Sal, P < 0.01), and a reduced running performance (27.29 [+ or -] 4.48 min Los vs. 52.47 [+ or -] 6.67 min Sal, P < 0.01), which was closely related to the increased BHR. Our data suggest that A[T.sub.1]-receptor blockade attenuates heat dissipation during exercise due to the higher T[T.sub.b]V, leading to a faster exercise-induced increase in [T.sub.b], thus decreasing running performance. tall vasodilation; fatigue; heat balance doi: 10.1152/ajpregu.00038.2006.