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Background Coronary microvessels (<300 μm in diameter) have been demonstrated to be important in the regulation of local resistance and flow. Recent studies also suggest that these microvessels are more responsive to physiological and pharmacological stimuli than conduit vessels. However, little is known regarding the relative sensitivity of different microvascular segments in response to flow (shear stress) and agonists. The goal of this study was to test the hypothesis that a longitudinal gradient for shear stress– and agonist-induced dilation exists in the coronary microcirculation.

Methods and Results Experiments were performed in four different sizes of porcine subepicardial coronary arterial microvessels: small arterioles (40±1-μm ID with resting tone); intermediate arterioles (60±1 μm); large arterioles (106±4 μm); and small arteries (179±9 μm). Vessels were isolated and cannulated to allow luminal …