HEAT-LOSS DURING COLD-EXPOSURE IN ADULT AND AGED C57BL 6J MICE/

Metabolic heat production (MHP), colonic temperature (Tco), and noneva porative (dry) heat loss were measured in ADULT and AGED C57BL/6J male mice during cold exposure. Dry heat loss was assessed as a differenti al temperature (Td) between incoming and outgoing air through the cham ber for indirect calorimetry. The average Td during cold exposure norm alized to surface area for ADULT mice was significantly higher than th at for the AGED animals (0.0618 +/- 0.0003 degrees C/cm(2) and 0.0553 +/- 0.0005 degrees C/cm(2), respectively). Linear regression analysis showed that at the same Tco AGED mice showed lower values of Td normal ized to surface area, indicating that at the same body temperature the y were losing less heat than ADULT animals. It was concluded that age- related decline in cold tolerance in mice is not due to a lack of abil ity to reduce heat loss during cold exposure. On the contrary, AGED an imals had lower heat loss in comparison with ADULT. We suggest that au gmentation of heat conservation mechanisms is an adaptive response to diminishing cold-induced heat production.