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 ce ntral ear (cutaneous) and femoral (non-cutaneous) arteries to histamin e were determined at 37 degrees C and 24 degrees C (cooling). Under re sting tension, both types of arteries contracted to histamine (10(-7)- 10(-3) M), and the sensitivity of ear arteries, but not of femoral art eries was lower at 24 than at 37 degrees C. Chlorpheniramine (10(-7) M ) blocked the contraction of both types of arteries to histamine at bo th temperatures. In ear arteries, endothelium removal or treatment wit h the nitric oxide synthase inhibitor N-G-nitro-L-arginine methyl este r (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 femo ral arteries precontracted with endothelin-1 (10(-8)-10(-7) M) and pre treated 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 bl ocked 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 an d relaxing H-2 receptors, probably located on smooth musculature, and (2) cooling reduces the contraction and increases the relaxation of cu taneous arteries to histamine: the reduction of this contraction could be caused by an augmented availability of endothelial nitric oxide, a nd the increment of this relaxation could be caused by an augmented se nsitivity of H-2, receptors of smooth musculature induced by cooling. These features do not seem to occur in deep vessels.