Time course of peripheral heterothermy in a homeotherm.
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.
D000222:Adaptation, Physiological; D000818:Animals; D001833:Body Temperature Regulation; D003080:Cold Temperature; D051381:Rats; D013997:Time Factors; D014661:Vasoconstriction; D014666:Vasomotor System / Q000502:physiology*