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CLINICAL RESEARCH

Identification of a Cytochrome P450 2C9-Derived Endothelium-Derived Hyperpolarizing Factor in Essential Hypertensive Patients

Department of Internal Medicine, University of Pisa, Pisa, Italy

Manuscript received September 14, 2005; revised manuscript received March 27, 2006, accepted April 11, 2006.

^_* Reprint requests and correspondence: Dr. Stefano Taddei, Department of Internal Medicine, University of Pisa, Via Roma, 67, 56100 Pisa, Italy. (Email: s.taddei{at}med.unipi.it).

OBJECTIVES: We assessed the role of cytochrome P450 2C9 (CYP 2C9)-derived endothelium-derived hyperpolarizing factor (EDHF) in the forearm microcirculation of essential hypertensive patients (EH) by utilizing sulfaphenazole (SUL), a selective CYP 2C9 inhibitor.

BACKGROUND: In EH patients, EDHF acts as a compensatory pathway when nitric oxide (NO) availability is reduced. Cytochrome P450 2C9 is a possible source of EDHF.

METHODS: In 36 healthy subjects (normotensive [NT]) and 32 hypertensive patients (HT), we studied forearm blood flow (strain-gauge plethysmography) changes induced by intraarterial acetylcholine (ACH) and bradykinin (BDK), repeated during N^G-monomethyl-L-arginine (L-NMMA) (100 µg/100 ml/min) or SUL (0.03 mg/100 ml/min). In HT, the effect of SUL on ACH and BDK was repeated during vitamin C (8 mg/100 ml/min). Sodium nitroprusside (SNP) was utilized as control.

RESULTS: In NT, vasodilation to ACH and BDK was blunted by L-NMMA and not changed by SUL. In contrast, in HT responses to ACH and BDK, reduced compared with NT, were resistant to L-NMMA. In these patients, SUL blunted vasodilation to ACH and to a greater extent the response to BDK. When retested with vitamin C, SUL was no longer effective on both endothelial agonists. In 2 final groups of normotensive control subjects, vasodilation to ACH or BDK residual to cyclooxygenase and L-NMMA blockade was further inhibited by simultaneous SUL infusion. Response to SNP, similar between NT and HT, was unaffected by SUL.

CONCLUSIONS: Cytochrome P450 epoxygenase-derived EDHF acts as a partial compensatory mechanism to sustain endothelium-dependent vasodilation in HT, particularly the BDK-mediated response, when NO activity is impaired because of oxidative stress.

Abbreviations and Acronyms   ACH = acetylcholine   BDK = bradykinin   BP = blood pressure   COX = cyclooxygenase   CYP 2C = cytochrome P450 epoxygenase   EDHF = endothelium-derived hyperpolarizing factor   EET = epoxyeicosatrienoic acid   FBF = forearm blood flow   L-NMMA = NG-monomethyl-L-arginine   NO = nitric oxide   SNP = sodium nitroprusside

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