- Koch, L G; Strick, D M; Britton, S L; Metting, P J
- To evaluate the competition between local autoregulation and reflex neurohumoral control of hindlimb blood flow (HLBF), the hindlimb vascular pressure-flow relationship was determined in nine dogs in response to a 10% decrease in mean arterial pressure (AP) imposed during both low (3.0 km/h, 0% grade) and high (5.5 km/h, 14% grade) intensities of treadmill exercise. HLBF was measured with a Doppler flow probe on the left external iliac artery, and AP was controlled with a gravity reservoir connected to the left carotid artery. A 10 +/- 2% reduction in AP for 25 min caused HLBF to decrease 25 +/- 2% during low-exercise intensity but only 10 +/- 2% during high-exercise intensity. The corresponding closed-loop gains (Gc) of HLBF regulation [Gc = 1 - (% delta hindlimb blood flow/% delta hindlimb perfusion pressure) were -1.6 +/- 0.4 and -0.06 +/- 0.2 during low- and high-exercise intensity, respectively. Autonomic ganglionic blockade (hexamethonium) increased the Gc during low-intensity exercise to 0.07 +/- 0.2. Antagonism of adenosine receptors (aminophylline) decreased the Gc of HLBF regulation during high-intensity exercise to -0.57 +/- 0.3. These data demonstrate that in response to an imposed decrease in AP, autonomic vasoconstriction overrides autoregulatory vasodilatory mechanisms during low-intensity exercise. HLBF regulation increases at a higher exercise intensity, in part due to adenosine, but autoregulation does not predominate over arterial pressure regulating mechanisms.
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