Central angiotensin receptor blockade impairs thermolytic and dipsogenic responses to heat exposure in rats

The effect of central angiotensin AT(1) receptor blockade on thermoregulation and water intake after heat exposure was investigated. Rats were placed in a chamber heated to 39 +/- 1 degreesC for 60 min and then returned to their normal cage (at 22 degreesC), and water intake was measured for 120 min. Artificial cerebrospinal fluid (5 mul) was injected intracerebroventricularly 60 min before heat exposure in five control rats. Colonic temperature increased from 37.22 +/- 0.21 to 40.68 +/- 0.31 degreesC after 60 min. In six rats injected intracerebroventricularly with 10 mug of the AT(1) antagonist losartan, colonic temperature increased from 37.41 +/- 0.27 to 41.72 +/- 0.28 degreesC after 60 min. This increase was significantly greater than controls (P < 0.03). Losartan-treated rats drank 1.1 +/- 0.4 ml of water compared with 5.9 +/- 0.77 ml (P < 0.002) drank by control animals, despite a similar body weight loss in the two groups. Central losartan did not inhibit the drinking response to intracerebroventricular carbachol in heated rats, suggesting that losartan treatment did not nonspecifically depress behavior. We conclude that central angiotensinergic mechanisms have a role in both thermoregulatory cooling in response to heat exposure and also the ensuing water intake.