ROLE OF THE ENDOTHELIUM IN THE RESPONSE TO CHOLINOCEPTOR STIMULATION OF RABBIT EAR AND FEMORAL ARTERIES DURING COOLING

The role of the endothelium in the effects of cooling on the response to cholinoceptor stimulation of the rabbit central ear (cutaneous) and femoral (non-cutaneous) arteries was studied using 2 mm long cylindri cal segments. Concentration-response curves for acetylcholine (10(-9)- 10(-5)M), methacholine (10(-9)-10(-5)M) and sodium nitroprusside (10(- 9)-10(-4) M) were isometrically recorded in arteries under conditions, with and without endothelium or following pretreatment with the nitri c oxide-synthesis inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME , 10(-6)-3 x 10(-4) M) at 37-degrees-C and at 24-degrees-C (cooling). Ear and femoral arteries showed endothelium-dependent relaxation to ac etylcholine and methacholine at 37-degrees-C and 24-degrees-C. The ext ent of relaxation of the control ear arteries, but not of the control femoral arteries, to acetylcholine and methacholine increased during c ooling. L-NAME (10(-6)-3 x 10(-4) M) reduced in a concentration-depend ent way the response of ear arteries to acetylcholine at both 37-degre es-C and 24-degrees-C, this reduction being more potent at 37-degrees- C. L-Arginine (10(-5)-10(-3) M) reversed in a concentration-dependent manner the inhibitor effects Of 10(-5) M L-NAME at both temperatures. Sodium nitroprusside caused a concentration-dependent relaxation in bo th arteries that was endothelium-independent. However, the extent of r elaxation to this nitrovasodilator in ear and femoral arteries was low er at 24-degrees-C. These results suggest that cooling augments the re activity of cutaneous (ear) arteries, but not that of non-cutaneous (f emoral) arteries to cholinoceptor stimulation by endothelium-mediated mechanisms. Cooling could therefore facilitate the stimulated release of endothelial nitric oxide in cutaneous vessels.