Evidences for the existence of endothelium-derived relaxing factor in the renal medulla

The basal levels of cGMP in renal medulla slices were enhanced when the slices were stimulated with both endothelium-dependent (acetylcholine) and endothelium-independent (molsidomine) vasodilators. When preincubated with NG-mono-methyl-L-arginine, a specific inhibitor of endothelium-derived relaxing factor, only the acetylcholine-stimulated increase was completely abolished. Furthermore, a preincubation with L-arginine, a selective precursor of endothelium-derived relaxing factor, enhanced the cGMP levels. The results indicate that the renal medulla, presumably the endothelial cells of the vasa recta, is able to produce endothelium-derived relaxing factor.