NO and the hypometabolic and hypothermic responses to hypoxia in the rat

Nitric oxide (NO) has been identified as a possible mediator of the thermoregulatory and respiratory responses to hypoxia. The present study was designed to assess the effects of an NO donor (S-nitroso-N-acetylpenicillamine, SNAP) injected systemically (0.5-2.0 mg/kg) in unanesthetized adult rats studied at ambient temperatures (Ta) of 26, 24, and 15 degrees C. The metabolic rate (VO2), ventilation (V), and colonic temperature (Tc) were recorded while the animals were exposed to normoxia or to hypoxia (FI(O2)=0.11). During normoxia, at all values of Ta, SNAP increased VO2 and V and the decrease in Tc observed following saline injection was prevented or attenuated. However, SNAP did not modify the hypometabolic, hypothermic, and hyperventilatory responses to hypoxia. We concluded that, confirming previous studies, NO may play a role in the control of VO2 and V in normoxia. The failure to observe any effect following the systemic NO donor injection during hypoxia may indicate opposing actions of the drug at different sites resulting in no net changes in ventilatory and metabolic responses to hypoxia.