Effect of oral organic nitrates on expression and activity of vascular soluble guanylyl cyclase

Thao-Vi Vu Dao1, Suvorava Tatsiana1, Kumpf Stephanie1, Bas Murat2, Weber Martina3, Oppermann Marc1, Kojda Georg1
1Institute for Pharmacology and Clinical Pharmacology, Düsseldorf, Germany, 2Department of Otorhinolaryngology, Heinrich-Heine-University, Düsseldorf, Germany, 3Division of Cardiology, Emory University, Atlanta, GA, USA

The regulation of vascular soluble guanylyl cyclase (sGC) expression by NO is still under discussion. In vitro, nitric oxide (NO) has been shown to downregulate the expression of sGC but it is unclear if this mechanism is operative in vivo and occurs during nitrate treatment. We investigated whether high dose isosorbide mononitrate (ISMN) or pentaerythritol tetranitrate (PETN) treatment changes vascular sGC expression and activity in vivo. New-Zealand White rabbits received a standard diet, 2mg or 200mg ISMN/kg BW/day for 16 weeks and C57BL/6 mice received standard diet, 6mg, 60mg or 300mg PETN/kg BW/day for four weeks. Absorption was checked by drug/metabolite plasma level determination. A new strain of transgenic mice with a vascular specific overexpression of eNOS was used to observe the effect of endogenous NO. Western blots of rabbit aortic rings showed similar protein levels of sGC-α1 (P=0.2790) and sGC-β1 (P=0.6900) in all groups. Likewise, ANOVA showed no difference of sGC expression in lungs of PETN-treated mice (P=0.0961 for sGC-α1 and P=0.3709 for sGC-β1 subunit). The activities of isolated sGC in response to SNAP (1μM-1mM) were identical in aortae of ISMN-treated rabbits (P=0.0775) and lungs of PETN-treated mice (P=0.6348). The aortic relaxation response to SNAP slightly decreased at high ISMN but not at high PETN. Transgenic mice showed a strong blood pressure reduction sensitive to eNOS-inhibition but again no change in sGC protein levels. However, sGC activity and phosphorylation of vasodilator-stimulated phosphoprotein was reduced. These data refute the hypothesis that therapeutic treatment with long acting NO-donors has a significant impact on regulation of vascular sGC expression and activity in vivo.