Cooling and alpha adrenergic responses in the saphenous vein of the rabbit

Abstract

Experiments were designed to determine the effects of cooling on alpha-1 and alpha-2 adrenergic responses in a cutaneous vein of the rabbit. Rings of saphenous vein were suspended in physiological salt solution for the recording of isometric force. Cooling (from 37-24°C) caused no significant increase in force in quiescent rings. Similarly, the same degree of cooling had no significant effect on the response to exogenous norepinephrine (10-9-10-5 M), whether under control conditions or in the presence of either the alpha-1 adrenergic antagonist prazosin (3 x 10-7 M) or the alpha-2 adrenergic antagonist rauwolscine (10-7 M). Contractions evoked by the alpha-1 adrenergic agonist phenylephrine were reduced, but those induced by the alpha-2 adrenergic agonist UK 14,304 (10-9-10-5 M) were unaffected by the same degree of cooling. Cooling augmented the response elicited by electrical field stimulation of the sympathetic nerves, although only under conditions of alpha-1 or combined alpha-1 and alpha-2 adrenergic blockade. Data obtained with the sympathomimetic tyramine suggest that both alpha-1 and alpha-2 adrenoceptors are innervated in this blood vessel. Together, the present data suggest that the effects of acute cooling on the saphenous vein of the rabbit, unlike that of the dog, are not mediated by changes in the affinity of postjunctional alpha-2 adrenoceptors.