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Coronary venular responses to flow and pressure
1Department of Medical Physiology, Texas A&M University Health Science Center, College Station 77843.
Insights
Porcine coronary venules dilate in response to increased blood flow, a response dependent on the endothelium and likely mediated by nitrovasodilators. This flow-induced dilation is crucial for regulating coronary microcirculation.
Area of Science:
- Cardiovascular Physiology
- Microcirculation Research
- Vascular Biology
Background:
- Previous studies confirmed endothelium-dependent vasodilation and myogenic responses in porcine coronary arterioles.
- The functional responses of coronary venules, particularly regarding flow and myogenic stimuli, remained largely uncharacterized.
- Understanding venular function is critical for a comprehensive view of coronary microvascular regulation.
Purpose of the Study:
- To investigate whether porcine coronary venules exhibit flow-induced dilation and myogenic responsiveness, similar to arterioles.
- To determine if venular flow-induced dilation is endothelium-dependent.
- To explore the potential role of nitrovasodilators in mediating venular flow-induced dilation.
Main Methods:
- Experiments utilized cannulated isolated porcine subepicardial coronary venules (80-120 microns diameter).
- Intraluminal pressure and flow were independently controlled using a dual perfusion reservoir system.
- Flow was induced by manipulating reservoir positions to create pressure gradients (delta P).
Main Results:
- Coronary venules displayed spontaneous tone at baseline intraluminal pressure.
- Stepwise increases in intraluminal flow induced gradual venular dilation, with a threshold at delta P = 1 cm H2O.
- Maximal dilation (93 ± 2%) was achieved at delta P ≥ 6 cm H2O; this response was abolished by endothelial damage (air bolus perfusion), and denuded venules constricted at high flows.
Conclusions:
- Porcine coronary venules demonstrate significant flow-induced dilation.
- This flow-induced dilation is critically dependent on an intact endothelium, suggesting mediator release.
- The findings support the hypothesis that coronary venules possess active regulatory mechanisms responsive to hemodynamic forces.
Abstract:
In previous studies, we demonstrated that both endothelium-dependent flow-induced vasodilation and endothelium-independent myogenic responses occur in porcine coronary arterioles. However, it was not established whether these responses are present in the coronary venular microcirculation. The aim of this study was to test the hypotheses that 1) coronary venules, like arterioles, exhibit flow-induced dilation and myogenic responsiveness, and 2) venular flow-induced dilation is endothelium-dependent and is mediated by the release of a nitrovasodilator. Experiments were performed in porcine subepicardial coronary venules, 80-120 microns in diameter, by using cannulated isolated vessel techniques to allow intraluminal pressure and flow to be independently controlled. Flow was initiated by simultaneously moving two perfusion reservoirs connected to the cannulating pipettes in equal amounts but in opposite directions. In the absence of flow, i.e., zero pressure gradient (delta P) between the two reservoirs, venules developed spontaneous tone to 75-80% of maximum diameter at 10 cm H2O intraluminal pressure. Venules gradually dilated in response to stepwise increases in flow (i.e., delta P). The threshold for the flow-induced dilation occurred at delta P = 1 cm H2O (flow = 3.5 nl/sec), and the maximal response (dilation to 93 +/- 2% of maximum diameter) occurred when delta P was elevated to > or = 6 cm H2O (flow = 21 nl/sec at delta P = 6 cm H2O). Flow-induced dilation was abolished after the endothelium was damaged by perfusion of an air bolus through the lumen. Vasoconstriction was observed when denuded venules were subjected to relatively high luminal flows (> or = 21 nl/sec).(ABSTRACT TRUNCATED AT 250 WORDS)