COOLING EFFECTS ON THE HISTAMINERGIC RESPONSE OF RABBIT EAR AND FEMORAL ARTERIES - ROLE OF THE ENDOTHELIUM

The effects of cooling on the isometric response of rabbit isolated central ear (cutaneous) and femoral (non-cutaneous) arteries to histamine were determined at 37 degrees C and 24 degrees C (cooling). Under resting tension, both types of arteries contracted to histamine (10(-7)-10(-3) M), and the sensitivity of ear arteries, but not of femoral arteries was lower at 24 than at 37 degrees C. Chlorpheniramine (10(-7) M) blocked the contraction of both types of arteries to histamine at both temperatures. In ear arteries, endothelium removal or treatment with the nitric oxide synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME, 10(-5) M) did not affect the contraction to histamine at 37 degrees C, but it reversed the decreased contraction at 24 degrees C. In femoral arteries, endothelium removal or L-NAME (10(-5) M) did not affect the response to histamine at 37 and 24 degrees C. Ear and femoral arteries precontracted with endothelin-1 (10(-8)-10(-7) M) and pretreated with chlorpheniramine (10(-5) M) relaxed to histamine (10(-7)-10(-4) M), and the sensitivity of this relaxation in ear arteries, but not in femoral arteries, increased at 24 degrees C. The relaxation of ear and femoral arteries to histamine was not modified by endothelium removal, L-NAME (10(-5) M) or meclofenamate (10(-5) M), but it was blocked by cimetidine (10(-6) M) at 37 degrees C and 24 degrees C. These results suggest: (1) ear and femoral arteries have contracting H-1 and relaxing H-2 receptors, probably located on smooth musculature, and (2) cooling reduces the contraction and increases the relaxation of cutaneous arteries to histamine: the reduction of this contraction could be caused by an augmented availability of endothelial nitric oxide, and the increment of this relaxation could be caused by an augmented sensitivity of H-2, receptors of smooth musculature induced by cooling. These features do not seem to occur in deep vessels.