Effect of chemical sympathectomy on coronary flow and cardiovascular adjustment to exercise in dogs
The exercise capacity and the increase of coronary and systemic hemodynamics under treadmill exercise were studied in 5 dogs, chemically sympathectomized with 6-hydroxy-dopamine.
Completeness of adrenergic denervation was verified by stimulation of the right stellate ganglion, by intravenous administration of tyramine, and by demonstration of supersensitivity to exogenous norepinephrine.
These dogs demonstrated a retarded adaptation of hemodynamics to a sudden start of exercise. A fall in mean arterial pressure below 45 mmHg within 10 to 15 sec lead to collapse. After a recovery period of 60–90 sec, moderate treadmill exercise could be continued; steady state attainment of hemodynamic parameters was considerably delayed.
A steady state of exercise with an O2-consumption (vO2) of 29.6±2.6 ml/min · kg and a cardiac outupt (CO) of 307±16 ml/min · kg was tolerated for at least 20 min.
An increase of vO2 up to 42.0±1.7 ml/min · kg and of CO up to 357±13 ml/min · kg under exercise was tolerated for 5 min with steady state, maximal heart rate being 160±4 min−1 at this level of exercise.
Mean arterial pressure and total peripheral resistance were significantly reduced at rest and during steady state of exercise as compared to controls prior to sympathectomy identical vO2, whereas CO remained unchanged.
The significant fall in left circumflex coronary flow was proportional to the decline in external heart work due to sympathectomy both at rest and under exercise.
Key words6-Hydroxydopamine Treadmill Exercise Sympatho-Adrenal system Exercise Capacity
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