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CLINICAL STUDY: ENDOTHELIAL FUNCTION

Tetrahydrobiopterin improves endothelial dysfunction in coronary microcirculation in patients without epicardial coronary artery disease

^a Department of Cardiovascular Medicine, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan

Manuscript received December 6, 2000; revised manuscript received March 29, 2001, accepted April 10, 2001.

Reprint requests and correspondence: Dr. Masahiro Mohri, Department of Cardiovascular Medicine, Kyushu University Graduate School of Medical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
mmohri{at}med.kyushu-u.ac.jp

OBJECTIVES

We aimed to determine whether intracoronary supplementation with nitric oxide (NO) synthase co-factor tetrahydrobiopterin (BH4) improves NO-dependent coronary microvascular dilation in patients with coronary risk factors but no significant organic stenosis.

BACKGROUND

Impaired coronary microvascular dilator reserve attributable to endothelial dysfunction plays an important role in the regulation of coronary blood flow (CBF).

METHODS

Fifteen patients were measured for CBF (Doppler-wire and quantitative coronary angiography). Stimulated release of NO in the coronary microcirculation was evaluated by percent increase in CBF (%CBF) at graded doses of intracoronary acetylcholine (1, 3, 10 and 30 µg/min). Measurements were repeated after intracoronary co-infusion of BH4 (4 mg/min) and acetylcholine.

RESULTS

The patients were divided into two groups on the basis of CBF responses to acetylcholine: those with "diminished" (%CBF <300%, n = 8) and "normal" (%CBF >300%, n = 7) flow responses. Tetrahydrobiopterin significantly (p < 0.0001) improved acetylcholine-induced increases in CBF in patients with diminished flow responses, but exerted no effect in those with normal flow responses. Among the 15 studied patients, the magnitude of flow improvement by BH4 was inversely correlated with baseline flow responses (p < 0.02). Microvascular dilator response to direct NO donor (isosorbide dinitrate) was not affected by BH4.

CONCLUSIONS

We demonstrated for the first time that intracoronary BH4 improved acetylcholine-induced microvascular dilator responses in patients with endothelial dysfunction in vivo. Thus, supplementation with BH4 may be a novel therapeutic means to increase NO availability for patients with coronary microvascular disease.

Abbreviations and Acronyms   BH4 = tetrahydrobiopterin   CAD = coronary artery disease   CBF = coronary blood flow   LCA = left coronary artery   NO = nitric oxide

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