Extraluminally applied acetylcholine and oxyhemoglobin on the release and action of EDRF

Acetylcholine applied intra- and extraluminally to the donor tissue (dog femoral artery segment with endothelium) produced a relaxation of the bioassay tissue (coronary artery strip without endothelium). Extraluminal acetylcholine was 1 44 as potent as intraluminal acetylcholine (10 −7 M). Extraluminal treatment with oxyhemoglobin halved the relaxation caused by acetylcholine applied intraluminally. Acetylcholine and oxyhemoglobin applied extraluminally appear to be translocated to the endothelium, resulting in vasodilatation via the release of endothelium-derived relaxing factor (EDRF) and attenuation of EDRF actions, respectively.