Contributions of baroreceptor reflex to the hypothermic effect of intraventricular angiotensin II in rats.

Abstract

The mechanisms of the hypothermic effect of angiotensin II (All) injected into the lateral ventricle were investigated in unanesthetized rats at an ambient temperature of 18°C. Mean blood pressure (BP), heart rate (HR), metabolic rate (M), colonic temperature (T01), and temperatures of the interscapular brown adipose tissue (TBAT), and the tail skin (TSk) were continuously monitored. All at a dose of 5 ug produced a sharp and marked elevation in BP accompanied by bradycardia, and a decrease of M and Tco1 in the sinoaortic baroreceptor intact rats. The difference between TBAT and Tool decreased significantly, which suggests a suppression of nonshivering thermogenesis of the BAT. TSk was not changed by the All injection. After sinoaortic deneravation, however, the decrease in Tco1 and M with All injection was significantly reduced despite a marked elevation in BP. In addition, intravenous arginine-vasopressin antagonist pretreatment suppressed the elevation in BP and the decrease in HR, Tool, and M after All injection. From these results, it is concluded that the hypothermia which occurred after All injection into the lateral ventricle can be largely attributed to the baroreflexive suppression of M, and to some extent to the direct effect on the thermoregulatory center in rats.

Effects of intraventricular neurotensin on blood pressure and heat balance in rats.

“…It has been shown that the baroreflex suppresses shivering and nonshivering thermogenesis of conscious animals in cool environments (HOHTOLA et al, 1980;NUNOMURA, 1983;SHIBATA, 1982;SHIDO et al, 1984;WASSERSTRUM and HERD, 1977). Recently, we observed that an intraventricular injection of angiotensin II produced a decrease in metabolism and a fall in body temperature with a concomitant rise in BP and bradycardia (SHIDO et al, 1985). Since hypothermia and metabolic suppression were markedly diminished in the sinoaortic denervated rats, the conclusion was that the hypothermic response to the central angiotensin II was attributed to the sinoaortic baroreflexive suppression of metabolism.…”

Endogenous angiotensin II and the regulation of oxygen consumption and colonic temperature in rats

“…Ang II treatment altered the activity of temperature sensitive neurons in the paraventricular nucleus and the preoptic area of rats (DeWald et al, 2002;Kiyohara et al, 1984;Travis and Johnson, 1993). Ang II injected into the brain of rats reduced core temperature (Kiyohara et al, 1984;Lin et al, 1980;Shido, et al, 1985aShido, et al, , 1985bWilson and Fregly, 1985b) although there have also been reports that ICV Ang II has no effect on core temperature . Ang II injected peripherally reduced core temperature and oxygen consumption, while increasing tail skin temperature (Cassis et al, 2002;Rowland, 1992, 1995;Fregly, 1985a, 1985b;Wright and Katovich, 1996).…”

“…Less well understood is a potential role for Ang II in the regulation of metabolic rate and body temperature. Early studies in rats demonstrated that Ang II decreased core temperature following either central (Kiyohara et al, 1984;Lin et al, 1980;Shido et al, 1985aShido et al, , 1985bWilson and Fregly, 1985b) or peripheral Fregly, 1985a, 1985b) administration. Following intracerebroventricular (ICV) injection, Ang II decreased the metabolic rate/oxygen consumption in rats (Lin et al, 1980).…”

“…At higher doses (10-40 mg) ICV injected Ang II caused a decrease in tail skin temperature (Lin et al, 1980) but at lower doses (1-5 mg) it caused an increase in tail skin temperature (Wilson and Fregly, 1985b) and dry heat loss (Shido et al, 1985b). Some of these effects of Ang II on temperature regulation may be due to the baroreceptor mediated response to its pressor effects (Shido, 1985a).…”

Role of Central Angiotensin II in Interleukin‐1‐Induced Fever in Rats

“…The role of central angiotensin II (AII) in body temperature regulation was documented in the 1980s. For example, central injection of AII was reported to produce hypothermia in rats, 1 rabbits 2 and monkeys 3 . These results suggested that AII acts as a temperature‐lowering substance in the brain.…”