Naltrexone attenuates plasma nitric oxide release following acute heat stress

Previous studies have shown that naltrexone attenuates morbidity and mortality in heat stress by inhibiting endogenous opioids. In this study, we hypothesized that naltrexone can decrease heat stress by attenuating nitric oxide release. Male Sprague–Dawley rats were pretreated with naltrexone or normal saline, and exposed to 45 °C for 25 min; controls were exposed to 25 °C. Colonic temperatures were recorded and plasma samples from an in-dwelling i.v. cannula were analyzed for nitrate/nitrite levels. Following heat stress, peak colonic temperature was significantly diminished ( P