SUDDEN VASOCONSTRICTION IN DENERVATED OR SYMPATHECTOMIZED PAWS EXPOSED TO COLD

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Abstract
A sudden, late fall of skin temp. was observed when denervated or sympathectomized paws of one unanesthetized dog and 16 lightly anesthetized cats were exposed to cold for prolonged periods. A corresponding abrupt rise of skin temp. was observed when the chilled extremities were exposed again to warm air. Analysis indicated that the vasoconstriction producing this sudden fall in skin temp. reduced blood flow to approx. 1/10 its previous value. The vasoconstriction appeared when the skin of the operated paws reached a critical temp. After preganglionic lumbar sympathectomy in the dog, this critical temp. remained constant at approx. 22[degree] + 2[degree]C, up to 130 days postoperative. After section of the sciatic nerve in cats, the critical temp. ranged between 19[degree] and 26[degree]C up to 2 days, and then rose to reach between 28 and 31[degree] C by 4 to 21 days postoperative. This effect of prolonged cooling appears to be due chiefly to locally increased sensitivity of the denervated blood vessels to cold because the reaction appeared at the usual critical temp. (a) when the adrenal glands were extirpated or inactive, (b) when the leg was disconnected from the body except for the procainized artery and vein, and (c) when only the paws were chilled while the body was kept warm enough to produce maximal vasodilatation in the normally innervated paws.