Transient peripheral warming accompanies the hypoxic metabolic response in the golden-mantled ground squirrel

Abstract

The hypoxic metabolic response of mammals involves a reversible metabolic suppression, possibly brought about by a reduction in the body temperature set-point. In the present study we tested the hypothesis that this is accompanied by a transient increase in heat loss that facilitates the decline in body temperature and metabolic rate. Peripheral heat distribution was assessed using infrared thermography to measure the surface temperatures of the golden-mantled ground squirrel at three different ambient temperatures (10, 22 and 30 degrees C). During early hypoxic exposure, surface temperatures increased dramatically in the feet, ears and nose, and this increase was more dramatic and prolonged at 22 degrees C than at the other two temperatures. These increases were associated with a fall in metabolic rate. Following this initial increase, surface temperatures decreased back to control values, and at 10 degrees C, the surface temperatures of the eyes and body decreased below normoxic levels. Subsequent normoxic recovery was not accompanied by transient changes in surface temperatures, despite large increases in metabolic rate associated with post-hypoxic shivering and thermogenesis. The temporal changes in surface temperature suggest that peripheral blood flow is initially increased during hypoxia, shifting heat away from the core to the periphery and thus facilitating cooling. These results are consistent with the hypothesis that hypoxia leads to a regulated fall in body temperature.