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Endothelium-dependent, flow-induced dilation of isolated coronary arterioles
L Kuo1, M J Davis, W M Chilian
1Department of Medical Physiology, College of Medicine, Texas A&M University, College Station 77843.
Insights
Coronary arterioles exhibit flow-mediated dilation, a response that competes with myogenic constriction. This study demonstrates that endothelial function is crucial for this dilation in small coronary vessels.
Area of Science:
- Cardiovascular Physiology
- Microcirculation Research
- Endothelial Function
Background:
- Flow-mediated dilation (FMD) is established in large coronary arteries.
- Its occurrence and interaction with myogenic constriction in coronary arterioles remain uncharacterized.
Purpose of the Study:
- To investigate FMD in subepicardial coronary arterioles.
- To determine if FMD competes with myogenic constriction.
- To elucidate the role of the endothelium in FMD of coronary arterioles.
Main Methods:
- Isolated subepicardial arterioles (40-80 microns) were cannulated.
- Myogenic responses were assessed across varying intraluminal pressures (IP).
- Flow was induced by pressure gradients (delta P), and responses were studied at different myogenic tones.
Main Results:
- Flow-induced dilation was observed, with a threshold at delta P = 4 cmH2O and maximum dilation at delta P = 20 cmH2O.
- The magnitude of dilation was greatest at intermediate myogenic tone (IP = 60 cmH2O).
- Endothelial removal abolished flow-induced and bradykinin-induced dilation, while preserving spontaneous tone and myogenic responses.
Conclusions:
- Coronary arterioles exhibit flow-mediated dilation.
- This response is dependent on endothelial function.
- Flow-mediated dilation in coronary arterioles interacts with, but does not abolish, myogenic constriction.
Abstract:
Flow-mediated dilation has been documented in large conduit coronary arteries but not in coronary arterioles. The goal of this study was to determine whether this response occurs in coronary arterioles and whether it competes with myogenic constriction. Subepicardial arterioles (40-80 microns) were isolated and cannulated with two glass micropipettes connected to independent reservoir systems. During zero flow, myogenic responses were studied over the range of intraluminal pressure (IP) between 20 and 140 cmH2O. Myogenic constrictions and dilations was observed when IP was increased (greater than 60 cmH2O) and decreased (less than 60 cmH2O), respectively. Flow was initiated by simultaneously moving the reservoirs in equal and opposite directions, thus generating a pressure gradient (delta P) without changing the mean luminal pressure (range delta P = 4-60 cmH2O). Flow-induced responses were studied at low, intermediate, and high myogenic tones by setting IP at 20, 60, and 100 cmH2O, respectively. The threshold for flow-induced dilation was delta P = 4 cmH2O, and maximum dilation was observed at delta P = 20 cmH2O. Red cell velocities in isolated arterioles at delta P of 4 and 60 cmH2O were 1.2 +/- 0.2 and 15.9 +/- 1.3 mm/s, respectively, which are within the range of those reported for coronary microvessels in vivo. The magnitude of the flow-induced dilation was greatest at the intermediate tone (60 cmH2O IP) but was attenuated at lower and higher IP. After mechanical removal of the endothelium, spontaneous tone and myogenic responses were preserved, but flow-induced dilation and bradykinin-induced dilation were abolished.(ABSTRACT TRUNCATED AT 250 WORDS)