Thermoregulatory responses of tailed and tailless rats to isoproterenol

Abstract

Colonic temperatures were measured in tailed and tailless rats at an ambient temperature (T_a) of 26 °C prior to and following administration of isoproterenol, a β-adrenergic agonist, at doses of 0, 12.5, 25.0, 50.0, and 100.0 μg∙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° higher than that of tailed rats after injection of 25.0, 50.0, and 100.0 μg 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 μg 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 μg isoproterenol per kilogram, the only dose tested. Mean colonic temperature of tailless rats was significantly higher, by 0.2–0.5°. than that of tailed rats during the initial 60 min of exposure to T_a 36 °C and during the first 40 min following removal from T_a 40 °C to T_a 28 °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.