title: Reflex versus autoregulatory control of hindlimb blood flow during treadmill exercise in dogs.
abstract: 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.
authors.affiliation: Department of Physiology and Biophysics, Medical College of Ohio, Toledo 43699-0008.
authors.forename: L G
authors.initials: LG
authors.lastname: Koch
authors.forename: D M
authors.initials: DM
authors.lastname: Strick
authors.forename: S L
authors.initials: SL
authors.lastname: Britton
authors.forename: P J
authors.initials: PJ
authors.lastname: Metting
mesh_terms: D000241:Adenosine / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004285:Dogs; D005260:Female; D005725:Ganglia, Autonomic; D005730:Ganglionic Blockers / Q000494:pharmacology; D006614:Hindlimb / Q000098:blood supply*; D006706:Homeostasis; D010805:Physical Conditioning, Animal; D012018:Reflex; D012039:Regional Blood Flow / Q000187:drug effects
chemical_list: D005730:Ganglionic Blockers; D000241:Adenosine