The role of spinal thermosensitive structures in the respiratory heat loss during exercise.

Abstract

Two dogs were prepared with spinal thermodes and hypothalamic guide tubes. The spinal thermodes could be used either for measuring the temperature of the peridural space of the spinal cord or for artificially altering this temperature. The hypothalamic guide tube was for measuring hypothalamic temperature. It was found that during exercise the temperature of the spinal cord increased and closely followed the temperature of the working muscles. The temperature of the hypothalamus increased only insignificantly. In a second series of experiments the spinal cord temperature of the same two dogs was artificially altered during exercise and the change in respiratory evaporative heat loss (REHL) was measured. It was found that spinal cord warming increased REHL both at rest and during exercise. At air temperatures of 30° and 32°C the sensitivity to spinal cord warming, as judged from the intercept and slope of calculated regression lines, was unaffected by exercise. At air temperatures of 25° and 27°C the sensitivityto spinal cord warming during exercise was the same as at the higher air temperature.—Spinal cord cooling was unable to inhibit the REHL during exercise. It is therefore concluded from these results that temperature signals generated in the spinal cord are not involved in the control of exercise induced increase in REHL.