THE TAIL OF THE RAT, IN TEMPERATURE REGULATION AND ACCLIMATIZATION

Abstract

The role of the tail of the Wistar white rat in its temperature regulation was studied, and a new index of acclimatization was found. Blood flow in the tail was measured by venous-occlusion plethysmography at environmental temperatures from 17 to 33 °C. There is an abrupt vasodilation between 27 and 30° with flow rising from less than 5 ml to about 40 ml/100 ml tissue per minute. Measurement of heat loss by a gradient calorimeter on the tail showed a similar reflex vasodilation at a critical vasodilation temperature (TCVD). After vasodilation the tail can lose up to 20% of the total heat production of the rat. The skin temperature of the tail was used as an index of vasodilation to determine whether the critical temperature shifted with acclimatization to 11 °C, 20 °C, and 30 °C. There is a decrease in TCVD of about 6° after acclimatization to cold (TCVD = 20 °C for 11 °C, 26 °C for 20 °C). After acclimatization to 30 °C, no vasodilation was found at temperatures up to 33 °C. The maximum heat loss of the tail is greatly increased after cold acclimatization. The mechanism of the shift is probably a change in sensitivity of thermal receptors on the tail, due to an increased vascularity (increased thermal conductivity) of the local tissues.