title: Increased neuronal nitric oxide synthase interaction with soluble guanylate cyclase contributes to the splanchnic arterial vasodilation in portal hypertensive rats.
abstract: Splanchnic arterial vasodilation represents the pathophysiological hallmark of the hemodynamic dysfunction observed in portal hypertensive states. The role of neuronal nitric oxide synthase (nNOS) in the splanchnic arterial vasodilation remains to be elucidated. We therefore investigated: (i) if nNOS is involved in the splanchnic arterial vasodilation; and (ii) the possible interaction of nNOS with soluble guanylate cyclase (sGC) in superior mesenteric arterial (SMA) beds in portal hypertensive rats. Portal hypertension was induced by partial portal vein ligation (PVL). To determine the role of nNOS, we removed endothelial layer and measured contractile response and nitric oxide (NO) release in the presence or absence of 7-nitroindazole (7-NI, 10 muM), an nNOS-specific inhibitor. In endothelium-removed vessels, nNOS inhibitor significantly increased the contractile response to methoxamine in SMA beds isolated from the portal hypertensive rats, compared to non-treated SMA beds (106.8 +/- 10.7 vs 86.8 +/- 7.2 mmHg, P = 0.003). This effect of nNOS inhibitor was accompanied with decreased NO production in SMA of portal hypertensive rats (321.3 +/- 18.6 vs 139.5 +/- 16.9 pmol/mL/min, P = 0.0001). Unlike endothelial NOS that is located in endothelial cells, nNOS protein is highly expressed in smooth muscle layers of SMA. Furthermore, there was a significant increase in ~90 kDa nNOS protein in the portal hypertensive group, compared to the sham-operated group (P < 0.01). Interestingly, this 90 kDa nNOS was coimmunoprecipitated with sGC. In conclusion, increased nNOS expression in smooth muscle layers of arteries in the splanchnic circulation may be an additional and more efficient pathway for the activation of sGC by NO, which sustains arterial vasodilation.
authors.affiliation: Hepatic Hemodynamic Laboratory, VA Connecticut Healthcare System, West Haven, CT;
authors.forename: So Young
authors.initials: SY
authors.lastname: Kwon
authors.forename: Roberto J
authors.initials: RJ
authors.lastname: Groszmann
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Iwakiri