A comparison of basal and agonist‐stimulated release of endothelium‐derived relaxing factor from different arteries

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Abstract
The release of endothelium‐derived relaxing factor (EDRF) from rabbit aorta and pig coronary artery vessels in response to acetylcholine (ACh), substance P (SP) and the calcium ionophore A23187 has been studied by means of a bioassay cascade system. A technique is described which allows the quantification of EDRF release rates from vessels of different sizes, perfused at different flow rates and with different donor‐recipient transient times. Rabbit aorta and pig coronary arteries, perfused at flow rates which equalise endothelial shear stress, released EDRF at a similar basal rate. In response to ACh, rabbit aortic endothelium released EDRF at a significantly greater maximum rate than pig coronary artery endothelium. In response to SP, both endothelium types released EDRF; SP was a significantly more potent agonist in pig coronary artery than in rabbit aorta, but maximum SP‐induced EDRF release from rabbit aorta was twice that of pig coronary artery. These data indicate that different endothelium types can release EDRF at widely different rates, according to the agonist used, and that the previously obtained lack of relaxant response to ACh in pig coronary artery was due to a lack of EDRF release rather than concomitant smooth muscle constriction.