Baroreflex-induced vasoconstriction in active skeletal muscle of conscious dogs.
We investigated the magnitude of baroreflex-mediated vasoconstriction in the hindlimbs of six conscious dogs at rest and during four levels of treadmill exercise ranging in intensity from mild (2 mph, 0% grade) to heavy (6 mph, 10% grade). Dogs were instrumented with vascular occluders on both common carotid arteries, an electromagnetic flow probe and vascular occluder on the terminal aorta, and a catheter in a branch of the femoral artery; aortic baroreceptors were intact. The responses to a 2-min carotid occlusion were observed at rest and after 3-5 min of exercise at each work rate. The increases in mean arterial pressure during carotid occlusion were similar at rest and at each level of exercise (26 +/- 4 to 35 +/- 3 mmHg; no significant difference). At rest, carotid occlusion caused only a small but significant decrease in terminal aortic vascular conductance (TAC) (-0.89 +/- 0.21 ml.min-1.mmHg-1, P less than 0.05). During mild exercise, baseline terminal aortic blood flow (TAQ) and TAC increased, and the reduction in TAC during carotid occlusion exceeded that observed at rest (-1.85 +/- 0.42 ml.min-1.mmHg-1, P less than 0.05). As exercise intensity increased, the magnitude of the reduction in TAC during carotid occlusion increased linearly with the baseline TAQ. At the highest work rate, approximately 59% of the increase in mean arterial pressure during carotid occlusion was due to the large decrease in TAC (-6.35 +/- 0.50 ml.min-1.mmHg-1). We conclude that the vasoconstriction of active skeletal muscle during the pressor response to bilateral carotid occlusion increased with exercise intensity.(ABSTRACT TRUNCATED AT 250 WORDS)
O'Leary
D S
DS
Department of Physiology and Biophysics, University of Washington, Seattle 98195.
Rowell
L B
LB
Scher
A M
AM
D000818:Animals; D002339:Carotid Arteries / Q000473:pathology / Q000601:surgery / Q000648:ultrastructure; D003243:Consciousness / Q000502:physiology*; D004285:Dogs; D005260:Female; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000294:innervation / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011311:Pressoreceptors / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology; D014661:Vasoconstriction / Q000502:physiology*