Neuromodulators and hypoxic hypothermia in the rat

This study was designed to assess if opioids or adenosine are involved in the hypometabolism induced by hypoxia in the rat. Accordingly, antagonists such as naloxone (NLX) for opioids or theophylline (THEO) for adenosine were injected into conscious adult rats acutely exposed to either ambient hypoxia (AHx, FIO2: 12%) at ambient temperatures of 26 or 9 degrees C, or to CO hypoxia (COHx, FICO = 0.05%) at an ambient temperature (Ta) of 9 degrees C. Oxygen consumption, ventilation, colonic temperature and shivering were recorded. The results show that with NLX, the degree of hypoxic hypometabolism was reduced with AHx at 26 degrees C and slightly decreased with COHx at 9 degrees C. With THEO, hypoxic hypometabolism was slightly reduced with AHx and COHx at 9 degrees C. The ventilatory response to AHx and COHx was not consistently affected by either NLX or THEO. It is concluded that adenosine and opioids play a minor role, in mediating AHx or COHx hypothermia, especially during cold exposure. (C) 1998 Elsevier Science B.V. All rights reserved.