Affiliation:
1. From Experimental Cardiology, Thoraxcenter, Cardiovascular Research Institute COEUR, Erasmus University Rotterdam, Rotterdam, The Netherlands.
Abstract
Abstract
—To date, no studies have investigated coronary vasomotor control of myocardial O
2
delivery (MD
o
2
) and its modulation by the autonomic nervous system in the porcine heart during treadmill exercise. We studied 8 chronically instrumented swine under resting conditions and during graded treadmill exercise. Exercise up to 85% to 90% of maximum heart rate produced an increase in myocardial O
2
consumption (MV̇
o
2
) from 163±16 μmol/min (mean±SE) at rest to 423±75 μmol/min (
P
≤0.05), which was paralleled by an increase in MD
o
2
, so that myocardial O
2
extraction (79±1% at rest) and coronary venous O
2
tension (cvP
o
2
, 23.7±1.0 mm Hg at rest) were maintained. β-Adrenoceptor blockade blunted the exercise-induced increase of MD
o
2
out of proportion compared with the attenuation of the exercise-induced increase in MV̇
o
2
, so that O
2
extraction rose from 78±1% at rest to 83±1% during exercise and cvP
o
2
fell from 23.5±0.9 to 19.6±1.1 mm Hg (both
P
≤0.05). In contrast, α-adrenoceptor blockade, either in the absence or presence of β-adrenoceptor blockade, had no effect on myocardial O
2
extraction or cvP
o
2
at rest or during exercise. Muscarinic receptor blockade resulted in a decreased O
2
extraction and an increase in cvP
o
2
at rest, an effect that waned during exercise. The vasodilation produced by muscarinic receptor blockade was likely due to an increased β-adrenoceptor activity, since combined muscarinic and β-adrenoceptor blockade produced similar changes in O
2
extraction and cvP
o
2
, as did β-adrenoceptor blockade alone. In conclusion, in swine myocardium, MV̇
o
2
and MD
o
2
are matched during exercise, which is the result of feed-forward β-adrenergic vasodilation in conjunction with minimal α-adrenergic vasoconstriction. β-Adrenergic vasodilation is due to an increase in sympathetic activity but may also be supported by withdrawal of muscarinic receptor–mediated inhibition of β-adrenergic coronary vasodilation. The observation that cvP
o
2
levels are maintained even during heavy exercise suggests that a decrease in cvP
o
2
is not essential for coronary vasodilation during exercise.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Cited by
107 articles.
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