Role of nitric oxide cGMP pathway in adrenomedullin-induced vasodilation in the rat

We previously reported that adrenomedullin (AM), a potent vasodilator peptide discovered in pheochromocytoma cells, stimulates nitric oxide (NO) release in the rat kidney. To further investigate whether the NO-cGMP pathway is involved in the mechanisms of AM-induced vasodilation, we examined the effects of E-4021, a cGMP-specific phosphodiesterase inhibitor, on AM-induced vasorelaxation in aortic rings and perfused kidneys isolated from Wistar rats. We also measured NO release from the kidneys using a chemiluminescence assay. AM (10(-10) to 10(-7) mol/L) relaxed the aorta precontracted with phenylephrine in a dose-dependent manner. Denudation of endothelium (E) attenuated the vasodilatory action of AM (10(-7) mol/L AM: intact (E+) -25.7 +/- 5.2% versus denuded (E-) -7.8 +/- 0.6%, P < 0.05), On the other hand, pretreatment with 10(-8) mol/L E-4021 augmented AM-induced vasorelaxation in the intact aorta (-49.0 +/- 7.9%, P < 0.05) but not in the denuded one. E-4021 also enhanced acetylcholine (ACh)-induced vasorelaxation in the rat intact aorta (10(-7) mol/L ACh -36.6 +/- 8.4% versus 10(-8) mol/L E-4021 + 10(-7) mol/L ACh -62.7 +/- 3.1%, P < 0.05). In perfused kidneys, AM-induced vasorelaxation was also augmented by preincubation with E-4021 (10(-9) mol/L AM - 15.4 +/- 0.6% versus 10(-8) mol/L E-4021 + 10(-9) mol/L AM -23.6 +/- 1.2%, P < 0.01). AM significantly increased NO release from rat kidneys (Delta NO: +11.3 +/- 0.8 fmol min(-1) g(-1) kidney at 10-9 mol/L AM), which was not affected by E-4021. E-4021 enhanced ACh-induced vasorelaxation (10(-9) mol/L ACh -9.7 +/- 1.7% versus 10(-8) mol/L E-4021 + 10(-9) mol/L ACh -18.8 +/- 2.9%, P < 0.01) but did not affect ACh-induced NO release from the kidneys. In the aorta and the kidney, 10(-4) moI/L of N-G-nitro-L-arginine methyl ester, an NO synthase inhibitor, and 10(-5) mol/L of methylene blue, a guanylate cyclase inhibitor, reduced the vasodilatory effect of AM. These results suggest that the NO-cGMP pathway is involved in the mechanism of AM-induced vasorelaxation, at least in the rat aorta and kidney.