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Ann Thorac Surg 2005;79:2065-2071
© 2005 The Society of Thoracic Surgeons

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Original article: Cardiovascular

Release of Nitric Oxide and Endothelium-Derived Hyperpolarizing Factor (EDHF) in Porcine Coronary Arteries Exposed to Hyperkalemia: Effect of Nicorandil

^a Department of Surgery, The Chinese University of Hong Kong, Hong Kong, China
^b Starr Academic Center, Providence Heart Institute, Department of Surgery, Oregon Health and Science University, Portland, Oregon
^c Wuhan Heart Institute, The Central Hospital of Wuhan, Wuhan, China

Accepted for publication November 17, 2004.

^_* Address reprint requests to Prof He, Department of Surgery, Block B, 5A, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, China (E-mail: gwhe{at}cuhk.edu.hk).

BACKGROUND: Although the detrimental effect of hyperkalemia on coronary endothelium has been reported, there is no direct evidence regarding the effect of hyperkalemic exposure on nitric oxide (NO) release from the coronary endothelium. In addition, it is unclear whether nicorandil, a K_ATP channel opener, used as hyperpolarizing cardioplegia or added in hyperkalemic cardioplegic solution may protect endothelial function during cardiac surgery. The present study was designed to clarify NO release and the function of endothelium-derived hyperpolarizing factor (EDHF) in coronary circulation with respect to the effect of hyperkalemia and nicorandil.

METHODS: Nitric oxide was measured by using a NO-specific electrode, and EDHF-mediated relaxation was investigated in a myograph. Substance P- and calcium ionophore A₂₃₁₈₇-induced NO release was compared in porcine left circumflex coronary arteries before and after 1-hour exposure to 20 mM potassium (K⁺) at 37°C. In coronary microarteries (diameter 200 to 450 µm), precontracted with U₄₆₆₁₉, in the presence of indomethacin (7 µM), N^G-nitro-L-arginine (300 µM), and oxyhemoglobin (20 µM), EDHF-mediated relaxation was induced by bradykinin (–10 to –6.5 log M) after incubation with Krebs (control) or 20 mM K⁺ with or without 10 µM nicorandil at 37°C for 1 hour.

RESULTS: Neither substance P (58.8 ± 5.0 versus 66.2 ± 7.2 nmol/L) nor A₂₃₁₈₇ (86.6 ± 9.0 versus 82.4 ± 9.2 nmol/L in control) induced NO release was altered by hyperkalemic exposure (p > 0.05). In contrast, EDHF-mediated relaxation was decreased from 84.2% ± 3.8% to 42.3% ± 6.0% (p < 0.001) that was partially restored by nicorandil (50.7% ± 5.5%, p < 0.05).

CONCLUSIONS: Exposure to potassium at 20 mM does not affect NO release but impairs EDHF-mediated relaxation in coronary arteries. Supplementation of nicorandil in hyperkalemic cardioplegia may provide a protective effect on EDHF-related endothelial function.

This article has been cited by other articles:

				Y.-Y. Dong, M. Wu, A. P.C. Yim, and G.-W. He Hypoxia-Reoxygenation, St. Thomas Cardioplegic Solution, and Nicorandil on Endothelium-derived Hyperpolarizing Factor in Coronary Microarteries Ann. Thorac. Surg., November 1, 2005; 80(5): 1803 - 1811. [Abstract] [Full Text] [PDF]