Instantaneous changes of alpha-adrenoceptor affinity caused by moderate cooling in canine cutaneous veins

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Abstract
Experiments were performed to investigate why cooling augments the contractile responses of superficial veins but depresses that of deep limb veins. Rings of dog''s saphenous veins were mounted in an organ chamber for isometric tension recording. Cooling (from 37 to 24.degree. C) depressed the tissular uptake of [3H]norepinephrine and potentiated the contraction caused by norepinephrine and sympathetic nerve stimulation. Potentiation persisted after inhibition of the disposition mechanisms for catecholamine and ouabain or iproveratril. The affinity of the .alpha.-adrenoceptors, to judge from the KA values for norepinephrine and from the pA2 (negative log of molar concentration of the antagonist which increased the ED50 by 2) values for the competitive antagonist phentolamine, was significantly greater at 24.degree. C than 37.degree. C. An instantaneous change in the affinity of .alpha.-adrenoceptors explains the augmented response of the cutaneous veins to adrenergic stimulation. By contrast, cooling depressed the response of femoral veins to norepinephrine and did not significantly affect the affinity of .alpha.-adrenoceptors in this preparation. This indicated that the temperature sensitivity of .alpha.-adrenoceptors in cutaneous veins was related to chronic exposure to variations in local temperature.

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