© 1997 by European Society of Cardiology
Copyright © 1997, European Society of Cardiology
Mechanism of coronary microvascular responses to metabolic stimulation
aDepartment of Surgery, University of Iowa, Iowa City, IA 52242, USA
bDepartment of Internal Medicine and the Cardiovascular Center, University of Iowa, and VA Medical Center, Iowa City, IA 52246, USA
* Corresponding author. Tel.: +1 (319) 339-7102; fax: +1 (319) 339 7135.
Previous studies from our laboratory have shown that coronary microvascular dilation to increased myocardial oxygen consumption (MVO2) is greater in vessels <100 µm. The mechanism responsible for this response is uncertain. Objectives: We tested the hypothesis that microvascular dilation to increased MVO2 is mediated by nitric oxide (NO). Since NO release may occur in response to increased shear, we also tested the hypothesis that metabolic byproducts released in response to increases in MVO2 will stimulate opening of the ATP-sensitive potassium channel. Methods: Changes in epicardial coronary microvascular diameters were measured in 9 dogs given NG-nitro-L-arginine (LNNA; 100 µM, topically), 7 dogs given glibenclamide (10 µM, topically) and 12 control (C) dogs during increases in metabolic demand using dobutamine (DOB, 10 µg/kg/min, i.v.) with rapid atrial pacing (PAC, 300 bpm). Diameters of arterioles were measured using intravital microscopy coupled to stroboscopic epi-illumination. Results: During the protocol, MVO2 increased to a similar degree in both experimental groups (LNNA and glibenclamide). Baseline hemodynamics and coronary microvascular diameters were similar between the two experimental groups and their respective control groups. In the presence of LNNA, coronary arteriolar (<100 µm) dilation (% change from baseline) was impaired during the protocol (DOB: vehicle 18±5, LNNA 2±2 [P<0.05]; DOB+RAP: vehicle 40±11, LNNA 6±2% [P<0.05]). In contrast, glibenclamide did not impair coronary microvascular responses to increased MVO2 despite similar increases in MVO2. Conclusion: This study indicates that coronary microvascular dilation in response to increased metabolic stimulation using dobutamine in conjunction with rapid pacing is mediated through a nitric-oxide-dependent mechanism and not ATP-sensitive potassium channels. These results may have important implications in pathological disease states where nitric oxide mechanisms are impaired, such as diabetes and hypertension.
KEYWORDS Coronary microcirculation; Dobutamine; EDRF; Arginine analogs; Glibenclamide; Potassium channel, ATP-sensitive; Nitric oxide; Endothelium; Intravital microscopy
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