Abluminal release and asymmetrical response of the rabbit arterial wall to endothelium-derived relaxing factor

A marked functional polarity of endothelial cells as well as an asymmetry of the vascular wall in response to vasoactive compounds is well established. Therefore, we investigated the polarity of endothelium-derived relaxant factor (EDRF) release from native endothelial cells, its diffusion characteristics, and its dilator effects on inner and outer muscle layers of the vascular wall in isolated rabbit arteries. Following exposure of rabbit aortae (with intact endothelium) to the EDRF stimulators acetylcholine, A23187, or thimerosal, a humoral dilator compound could be assayed in the adventitial superfusate of the vessels. The vasodilator effects were blocked by the EDRF inhibitors hemoglobin, dithiothreitol, and gossypol. Penetration of the dilator through the arterial wall following stimulation by acetylcholine, A23187, or thimerosal was observed only when dilator EDRF activity in the luminal perfusate was maximal. Luminally administered EDRF, released from cultured endothelial cells, did not cross the aortic wall in detectable amounts. EDRF (from cultured cells) elicited significantly smaller dilations (9 +/- 4%) when applied to the adventitial side of endothelium-denuded rabbit aortae or femoral arteries as compared with luminal application (92 +/- 7%). In contrast, sodium nitroprusside was equieffective by both routes of administration. We conclude that EDRF in native endothelial cells is released in both luminal and abluminal directions and can penetrate the entire vascular wall. However, the lengthy diffusion time and the decreasing sensitivity of outer smooth muscle layers suggest that mechanisms other than EDRF diffusion contribute significantly to the propagation of endothelium-mediated relaxation through the arterial wall.