Central application of a nitric oxide donor activates heat defense in the rabbit

In chronically instrumented, conscious rabbits at moderately warm ambient thermal conditions, infusion of the NO-donor SIN-1 into the anterio-ventral 3rd cerebral ventricle (1-2 microg/min per kg BW, 2-4 microl/min, 30 min) initiated a co-ordinated activation of autonomic heat loss mechanisms, as indicated by the rise in ear skin temperature and by increases in panting frequency and respiratory evaporative water loss, while oxygen consumption decreased slightly. The heat loss responses were similar to those attributed to NO in studies employing systemic application of NO-donors. Different from NO acting peripherally, which causes arterial hypotension and tachycardia, centrally acting NO induced arterial hypertension and bradycardia. The observation of the same heat loss responses despite opposing circulatory actions suggests that NO is specifically involved in thermoregulation as a central activator of heat defense mechanisms.