METABOLIC RESPONSE TO AMBIENT-TEMPERATURE AND HYPOXIA IN SINOAORTIC-DENERVATED RATS

Metabolic response to ambient temperature and hypoxia in sinoaortic-de nervated rats. Am. J. Physiol. 266 (Regulatory Integrative Comp. Physi ol. 35): R387-R391, 1994. - We tested the hypothesis that the sinoaort ic afferents may contribute to normoxic thermogenesis and to the magni tude of the hypometabolic response to hypoxia. Adult rats were either sinoaortic denervated (SAX; n = 20) or sham operated (Sham; n = 20). A few days after the operation, gaseous metabolism [O-2 uptake (VO2) an d CO2 production (VCO2)] was measured with an open-flow system at ambi ent temperatures (T-amb) Of 20, 25, 30, and 35 degrees C as the animal was resting awake. At thermoneutrality (T-amb 30 degrees C) or higher T-amb there was no difference in VO2 or VCO2. Below thermoneutrality, metabolic rate was significantly lower in SAX than in Sham animals (- 14 and -16% at 20 and 25 degrees C, respectively). Colonic temperature and arterial PO2 were also slightly less, whereas arterial PCO2, and pH, mean arterial pressure, and heart rate did not differ significantl y between the two groups. Exposure to acute hypoxia (10% inspired O-2, 20-30 min) at T-amb 20 and 25 degrees C significantly reduced VO2, in both groups to a similar value; hence, at either T-amb, the metabolic drop during hypoxia in Sham animals was larger than that in SAX anima ls. Hypercapnia (5% CO2 breathing) did not change VO2, in either group . We conclude that in the rat at T-amb slightly below thermoneutrality , the sinoaortic afferents 1) provide a small but significant contribu tion to normoxic thermogenesis and 2) are not required for the manifes tation of the drop in metabolism during hypoxia.