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Background: The Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) indicated that thiazide-type diuretics are superior in preventing cardiovascular diseases. Nitric oxide derived from the endothelium is a protective principle in the vasculature. We therefore wanted to find out whether thiazide diuretics enhance the endothelial NO system in vivo and/or in vitro and whether this contributes to the advantage of this class of drugs. Methods and Results: In human endothelial EA.hy 926 cells stably transfected with a 3.5 kb promoter fragment of human endothelial-type NO synthase (eNOS), the thiazide diuretic hydrochlorothiazide did not have any effect on eNOS promoter activity (1 nmol/L – 100 µmol/L, 6 h and 24 h treatment, luciferase reporter gene assay). Hydrochlorothiazide at concentrations from 10 nmol/L – 100 µmol/L did not change the expression of eNOS mRNA in EA.hy 926 cells (quantitative real-time RT-PCR, qRT-PCR). NO production, determined with electron paramagnetic resonance (EPR) spin trapping, did not changed in response to hydrochlorothiazide in EA.hy 926 cells, either. These results suggested that hydrochlorothiazide has no direct effect on the endothelial NO system, but this does rule out the possibility that diuretics could affect vascular NO system indirectly by inducing systemic changes. To test the later issue, we treated the spontaneously hypertensive rats (SHR) with hydrochlorothiazide. After a treatment of SHR for there weeks at doses 50 and 80 mg/kg/day of in chow, eNOS mRNA expression in the aorta was analyzed with qRT-PCR, NO production in the aorta and liver was determined with EPR and nitrite levels with NO chemiluminescence (NO-Analyzer). Neither eNOS expression nor NO production was changed by hydrochlorothiazide treatment. Conclusion: Hydrochlorothiazide has no effect on the endothelial NO system, neither in vitro, nor in vivo. The advantages of the thiazide diuretics seem to be independent on the endothelial NO system.
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J. Vasc. Biol. 42, Sup:2 (2005) p36