Effects of catecholamines on isolated canine facial veins

The buccal segment of the canine facial vein which was precontracted moderately with prostaglandin F2 alpha relaxed to different extents in response to dopamine (DA), norepinephrine (NE), epinephrine (Epi) and isoproterenol (Isp). Propranolol (10(-6) M) reversed the relaxation responses to contractions. In the presence of an alpha-adrenoceptor blockade and inhibitors of neuronal and extraneuronal uptakes, the four catecholamines relaxed the vein fully, and the order of pD2 values was Isp (8.34) greater than Epi (7.53) approximately equal to NE (7.50) much greater than DA (5.31). The results indicate that in the canine facial vein, beta-adrenoceptors predominate over alpha-adrenoceptors, and the subtype of beta-adrenoceptor may be the beta 1-type.