Thermoregulatory responses of tailed and tailless rats to isoproterenol

Colonic temperatures were measured in tailed and tailless rats at an ambient temperature (Ta) of 26 degrees C prior to and following administration of isoproterenol, a beta-adrenergic agonist, at doses of 0, 12.5, 25.0, 50.0, and 100.0 micrograms.kg-1. There was no significant difference between the colonic temperatures of tailed and tailless rats before drug injection. However, mean colonic temperature of tailless rats increased to a maximal level approximately 0.3 degrees higher than that of tailed rats after injection of 25.0, 50.0, and 100.0 micrograms isoproterenol per kilogram. The duration of the hyperthermic response was 50-60 min longer in tailless than tailed rats after administration of 50 and 100 micrograms isoproterenol per kilogram. The rate of oxygen consumption (heat production) increased by 4.5 mL.min-1.kg-0.75 in both tailed and tailless rats after administration of 50 micrograms isoproterenol per kilogram, the only dose tested. Mean colonic temperature of tailless rats was significantly higher, by 0.2-0.5 degrees than that of tailed rats during the initial 60 min of exposure to Ta 36 degrees C and during the first 40 min following removal from Ta 40 degrees C to Ta 28 degrees C. These results suggest that the tail of the rat is required for short-term maintenance of colonic temperature during both external and internal heat stresses.