RELATIONSHIP BETWEEN BODY CORE AND PERIPHERAL TEMPERATURES AT THE ONSET OF THERMOREGULATORY RESPONSES IN RATS

The relationships between body core temperature and environmental temp erature (T(a)) at the onset of tail skin vasodilation, thermally-induc ed salivary secretion and cold-induced thermogenesis were examined in rats. Hypothalamic temperature (T(hy)) was measured as an index of bod y core temperature. Internal body heating and cooling were made using an intravenous thermode chronically implanted in the inferior vena cav a at various T(a)s. External heating and cooling were made by changing T(a) at a constant rate, while T(hy) was controlled at constant level s with the thermode. Internal heating induced tail skin vasodilation b ut not thermally-induced salivary secretion, and internal cooling indu ced cold-induced thermogenesis. External warming caused tail skin vaso dilation and thermally-induced salivary secretion, but external coolin g failed to induce cold-induced thermogenesis. There were significant correlations between T(hy) and T(a) at the onset of tail skin vasodila tion, thermally-induced salivary secretion and cold-induced thermogene sis. When T(a) was taken as an indicator of thermal input from the ski n, the ratios of the potency of inputs from the body core and skin wer e estimated to be between 8:1 and 6:1 at the onset of tail skin vasodi lation, 8:1 at the onset of thermally-induced salivary secretion, and 5:1 for the control of cold-induced thermogenesis. These results sugge st that, in rats, the contribution of thermal input from the skin to t he onset of thermoregulatory responses is relatively small.