里中 弘志

Adrenomedullin (AM) is a potent vascular wall-derived vasorelaxing peptide which induces the release of nitric oxide (NO). To explore the role of endogenous AM in vascular function, we examined the effects of acetylcholine (ACh), AM, and AM receptor antagonists [AM (22-52), and calcitonin gene-related peptide (CGRP) (8-37)] on the isometric tension of aortic rings isolated from AM transgenic (TG) and knockout (KO) mice and wild type littermates (WT). ACh and AM caused a dose-dependent reduction of the isometric tension of aortic rings, but the degree of vasodilatation was smaller in TG than in KO or WT (%&Delta;tension [10^-6 mol/l ACh]: KO -69&plusmn;10%, WT -39&plusmn;8%, TG -29&plusmn;1%, p <0.01). On the other hand, N^G-nitro-L- arginine methyl ester, an NO synthase inhibitor, induced greater vasoconstriction in TG (%&Delta;tension 10^-5 mol/l: KO +78&plusmn;16%, WT +99&plusmn;27%, TG +184&plusmn;20%, p <0.01), whereas E-4021, a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase inhibitor, caused greater vasodilation in TG mice. Both AM antagonists increased tension in TG to a greater extent than in KO or WT mice (%&Delta;tension [10^-6 mol/l CGRP (8-37)]: KO +24&plusmn;5%, WT +51&plusmn;6%, TG +75&plusmn;7%, p <0.01). Endothelial denudation of the aorta diminished the vasoconstriction caused by the AM antagonists. In conclusion, the amounts of AM expressed in the aortic endothelium influenced baseline NO release. AM antagonists increased vascular tone in WT as well as in TG, suggesting that endogenous AM plays a physiological role in the regulation of aortic tone. (Hypertens Res 2003; 26 (Suppl): S79-S84)

It is well known that angiotensin II (Ang II) is implicated in the phenotypic modulation and hypertrophy of vascular smooth muscle cells (VSMCs). To study the mechanisms by which Ang II contributes to the pathological changes of VSMCs, we examined whether Ang II stimulated myocyte enhancer factor 2 (MEF2)- and calcineurin/nuclear factor of activated T cell (NFAT)-dependent transcriptional activation of genes in VSMCs. Ang II increased the DNA binding activity of MEF2A and its expression at the protein level. Ang II induced c-jun promoter activity, and this increase was inhibited by dominant-negative mutants of MEF2A and mitogen-activated protein kinase kinase 6 but not by calcineurin inhibitors. Ang II stimulated NFAT DNA binding activity and NFAT-dependent gene transcription, and these effects of Ang II were inhibited by calcineurin inhibitors. Furthermore, Ang II induced the promoter activity of the nonmuscle-type myosin heavy chain B gene, which we used as a marker of the dedifferentiated state of VSMCs, and this increase was inhibited by calcineurin inhibitors but not by the dominant-negative mutants of MEF2A or mitogen-activated protein kinase kinase 6. Finally, Ang II increased protein synthesis. and this increase was inhibited by infection with an adenovirus construct that expresses the dominant-negative mutant of MEF2A but not by calcineurin inhibitors. These results suggest that Ang II stimulates the MEF2- and calcineurin/NFAT-dependent pathways and that these pathways have distinct roles in VSMCs.

Adrenomedullin (AM) is a potent depressor peptide whose vascular action is suggested to involve nitric oxide (NO) release. To explore the role of endogenous AM in vascular and renal function, we examined the effects of acetylcholine (ACh), AM, and AM receptor antagonists AM(22-52) and CGRP(8-37) on the renal perfusion pressure (RPP) of kidneys isolated from AM transgenic (TG)/heterozygote knockout (KO) mice and wild-type littermates (WT). Furthermore, we evaluated the renal function and histology 24 hours after bilateral renal artery clamp for 45 minutes in TG, KO, and WT mice. Baseline RPP was significantly lower in TG than in KO and WT mice (KO 93.4 +/- 4.6, WT 85.8 +/- 4.2, TG 72.4 +/- 2.4 mm Hg [mean +/- SE], P &lt; 0.01). ACh and AM caused a dose-related reduction in RPP, but the degree of vasodilatation was smaller in TG than that in KO and WT (%DeltaRPP 10(-7) mol/L ACh: KO -48.1 +/- 3.9%, WT -57.5 +/- 5.6%, TG -22.8 +/- 4.8%, P &lt; 0.01), whereas N-nitro-L-arginine methyl ester (L-NAME) caused greater vasoconstriction in TG (%DeltaRPP 10(-4) mol/L: KO 33.1 +/- 3.3%, WT 55.5 +/- 7.2%, TG 152.6 +/- 21.2%, P &lt; 0.01). Both AM antagonists increased RPP in TG to a greater extent compared with KO and WT mice (%DeltaRPP 10(-6) mol/L CGRP(8-37): KO 12.8 +/- 2.6%, WT 19.4 +/- 3.6%, TG 41.8 +/- 8.7%, P &lt; 0.01). In mice with ischemic kidneys, serum levels of urea nitrogen and renal damage scores showed smaller values in TG and greater values in KO mice (urea nitrogen: KO 104 +/- 5&gt;WT 98 +/- 15&gt;TG 38 +/- 7 mg/dL, P &lt; 0.05 each). Renal NO synthase activity was also greater in TG mice. However, the differences in serum urea nitrogen and renal damage scores among the 3 groups of mice were not observed in mice pretreated with L-NAME. In conclusion, AM antagonists increased renal vascular tone in WT as well as in TG, suggesting that endogenous AM plays a role in the physiological regulation of the vascular tone. AM is likely to protect renal tissues from ischemia/reperfusion injury through its NO releasing activity.