TY - JOUR
T1 - Coronary α1-adrenergic constrictor tone varies with intensity of exercise
AU - Dodd-O, Jeffrey M.
AU - Gwirtz, Patricia A.
N1 - Copyright:
Copyright 2007 Elsevier B.V., All rights reserved.
PY - 1996
Y1 - 1996
N2 - This study tested the hypothesis that an α-adrenergic coronary constrictor tone increase with the intensity of exercise and impose a limitation on transmural myocardial blood flow and contractile function during strenuous levels of exercise. Nine (9 dogs are chronically instrumented to measure left circumflex blood flow (CBF), global myocardial contractile function (dP/dt(max)), and regional myocardial contractile function (maximal rate of segmental shortening, dL/dt(max)). The dogs were subjected to a graded submaximal exercise test with increasing workloads encompassing 4.8 kph and 6.4 kph, 0, 4, 8, 12, and 16% incline. On separate days, either vehicle (sterile water) or the specific α1-adrenergic receptor antagonist prazosin (1 μg · kg-1 · min-1) was infused into the circumflex artery during exercise. Removal of an α1-receptor mediated coronary constrictor tone resulted in a 15 ± 7%, 24 ± 9%, and 35 ± 10% greater increase in CBF compared with vehicle at the three most strenuous levels of exercise, respectively. Regional left ventricular blood flow was measured using labeled microspheres in four (4) additional dogs. Endocardial and epicardial blood flow increased equally by 16% during exercise after prazosin, such that the endocardial/epicardial flow ratio did not change. The augmentation in CBF after α1-blockade was associated with significant increases in both regional and global left ventricular contractile function. These studies indicate that a uniformly distributed transmural coronary α1- constrictor tone increases in magnitude with increasing levels of exercise intensity and, as a result, imposes a significant limitation on myocardial function.
AB - This study tested the hypothesis that an α-adrenergic coronary constrictor tone increase with the intensity of exercise and impose a limitation on transmural myocardial blood flow and contractile function during strenuous levels of exercise. Nine (9 dogs are chronically instrumented to measure left circumflex blood flow (CBF), global myocardial contractile function (dP/dt(max)), and regional myocardial contractile function (maximal rate of segmental shortening, dL/dt(max)). The dogs were subjected to a graded submaximal exercise test with increasing workloads encompassing 4.8 kph and 6.4 kph, 0, 4, 8, 12, and 16% incline. On separate days, either vehicle (sterile water) or the specific α1-adrenergic receptor antagonist prazosin (1 μg · kg-1 · min-1) was infused into the circumflex artery during exercise. Removal of an α1-receptor mediated coronary constrictor tone resulted in a 15 ± 7%, 24 ± 9%, and 35 ± 10% greater increase in CBF compared with vehicle at the three most strenuous levels of exercise, respectively. Regional left ventricular blood flow was measured using labeled microspheres in four (4) additional dogs. Endocardial and epicardial blood flow increased equally by 16% during exercise after prazosin, such that the endocardial/epicardial flow ratio did not change. The augmentation in CBF after α1-blockade was associated with significant increases in both regional and global left ventricular contractile function. These studies indicate that a uniformly distributed transmural coronary α1- constrictor tone increases in magnitude with increasing levels of exercise intensity and, as a result, imposes a significant limitation on myocardial function.
KW - CORONARY BLOOD FLOW
KW - LEFT VENTRICULAR FUNCTION
KW - PRAZOSIN
UR - http://www.scopus.com/inward/record.url?scp=9044240047&partnerID=8YFLogxK
U2 - 10.1097/00005768-199601000-00015
DO - 10.1097/00005768-199601000-00015
M3 - Article
C2 - 8775356
AN - SCOPUS:9044240047
SN - 0195-9131
VL - 28
SP - 62
EP - 71
JO - Medicine and Science in Sports and Exercise
JF - Medicine and Science in Sports and Exercise
IS - 1
ER -