Herbimycin A attenuates apoptosis during heat stress in rats

Expression of heat shock proteins (HSPs) as a heat stress response is associated with acquisition of thermotolerance. Herbimycin A is a tyrosine kinase inhibitor that has been shown to induce HSPs. The present study aims to investigate the effects of herbimycin A on thermotolerance in rats subjected to heat stress exposure. Herbimycin A induced hsp70 to peak levels 12 h post-injection in rats without heat stress. No change in hsp70 levels was observed in the vehicle- and saline-treated rats. In rats exposed to heat stress at 45 degrees C for 25 min, 12 h post-treatment, lower peak temperatures were attained in herbimycin A-treated group as compared to the vehicle- and saline-treated groups. Terminal transferase-mediated d-UTP nick end labeling (TUNEL) showed that a significant decrease in apoptosis of hepatocytes in herbimycin A-treated rats as compared to the vehicle- and saline-treated rats. Caspase-3 activation was also lower in herbimycin A-treated rats, compared to the vehicle- and saline-treated rats. The present study has demonstrated that herbimycin A is effective for development of thermotolerance and therefore protects rats from heat stress.

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 degrees C for 25 min; controls were exposed to 25 degrees 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 < 0.05) in naltrexone-treated rats compared to saline-treated rats. Plasma nitrate/nitrite levels were significantly lower (P < 0.05) in naltrexone-treated rats compared to saline-treated rats. These findings suggest that naltrexone is able to attenuate the rise in plasma nitric oxide levels commonly observed after heat stress.