AJP - Regulatory, Integrative and Comparative Physiology, Vol 239, Issue 1 126-R129, Copyright © 1980 by American Physiological Society
Time course of peripheral heterothermy in a homeotherm
R. T. Brown and J. G. Baust
The integrity of the peripheral heterothermic response was monitored in
adult Sprague-Dawley rats during cold acclimation. Subcutaneous peripheral
temperature gradients were simultaneously recorded in the hindlimbs. One
limb was exposed to room temperature (22 +/- 2 degrees C) while the
contralateral limb was gradually cooled to 0 +/- 1 degrees C. Noncontrols
were acclimated at 5 +/- 1 degrees C for periods up to 35 days. Controls
responded to the cooling regimen (25 to 0 degrees C at 0.5 degrees C .
min-1) in a "poikilothermic" manner indicating local cold-induced
vasoconstriction (CIVC). CIVC was not released until tissue temperatures
reached 22,3 +/- 2.5 degrees C whereupon nonpatterned limb temperature
fluctuations, Lewis' hunting response, were often initiated. The hunting
response occurred synchronously in the contralateral warmed limb despite
its elevated temperature. The experiments revealed a progressive decrease
in the intensity of heterothermy indicative of an earlier onset of
cold-induced vasodilation as well as increased resistance to tissue cooling
with increasing acclimation time. Following 21 days at 5 degrees C, limb
exposure to 0 degrees C resulted in a 2-4 degrees C drop in tissue
temperature. The time course of the diminution in peripheral heterothermy
is discussed. In addition, evidence supporting the hypothesis of a central
component in the regulation of the hunting response is presented.
