Constriction of Isolated Arteries and Their Vasa Vasorum Produced by Low Temperatures

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Abstract
The effect of cold and of cooling upon 136 swine and 20 dog carotid and femoral arteries was studied using an angioplethysmokymo-graphic method. Constriction of the arterial wall is a function of the rate of cooling rather than of the actual temp. of the tissue. Cooling the arteries at 4[degree] to 6[degree]C/min. produces up to 35% volume vasoconstriction of swine carotid arteries. Lesser cooling rates produce little or no constriction. Constriction of the vasa vasorum, in contrast, is a function of the temp. of the tissue and not of the rate of cooling. At 17[degree], flow thru the vasa vasorum is 17% of values at 37[degree]. Analysis of these results in terms of Poiseuille''s Law indicates that active constriction of the vasa vasorum occurs primarily upon lowering the temp. from 37[degree] to 27[degree] because the increased viscosity of the perfusate can account for only 28% of the observed decrease in flow at 27[degree] while it accounts for over 90% of the decrease between 27[degree] and 17[degree]. Vasoconstriction of the arteries to epinephrine, acetylcholine and histamine at 17[degree] is prolonged 400_600% over values at 37[degree]. Prolongation is due to slow contraction as well as slow relaxation of the vascular smooth muscle. The one normal human artery studied showed changes in its reactivity closely comparable to the animal arteries studied. The close correlation of these in vitro results with previous in vivo work is analyzed in terms of the physiology of the Hunting Reaction.

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