CONTRIBUTION OF ARTERIAL FEED VESSELS TO SKELETAL-MUSCLE FUNCTIONAL HYPEREMIA

The purpose of this study was to determine whether dilation of arteria l vessels preceding the microcirculation contributes differentially to increases in skeletal muscle blood flow during contractions in anesth etized sedentary (SED) or trained (TR) rats. Experiments were performe d in the spinotrapezius muscle of adult male Sprague-Dawley rats. Befo re and immediately after muscle contractions (2, 4, or 8 Hz), intravas cular pressures, red blood cell velocities, and vessel diameters were measured in terminal feed arteries at a site before penetration into t he tissue. Pressure was also measured in the accompanying vein. Contra ction-induced changes in vascular resistance were calculated for upstr eam (Rup), spinotrapezius muscle microvascular (Rst), and downstream s egments. At rest, Rup accounted for less (32 vs. 40%) and Rst for more (59 vs. 47%) of total resistance in TR than in SED rats. At 8 Hz, con tractions produced significantly greater functional dilation (SED, 138 +/- 14 mu m; TR, 178 +/- 12 mu m) and hyperemia (SED, 11.9 +/- 3.2 X control; TR, 16.8 +/- 3.1 X control) in TR than in SED rats. Inflow pr essures did not change, and outflow pressures increased significantly with contractions. Rup and Rst each decreased 60-80% after 2-Hz contra ctions and >90% after 8-Hz contractions. Therefore, feed artery dilati on contributes significantly to functional hyperemia in the rat spinot rapezius muscle. Furthermore, it appears that aerobic exercise trainin g results in a redistribution of segmental vascular resistance between feed vessels and the microcirculation.