Tonic influence of the sympathetic nervous system on myocardial reactive hyperemia and on coronary blood flow distribution in dogs.

In two groups of dogs we studied the effect of right and/or left stellectomy on myocardial reactive hyperemia (RH) and on coronary blood flow distribution. In the first group of 14 conscious dogs, the percent repayment of flow debt produced by a 10-second occlusion of the left circumflex coronary artery was recorded with a Doppler ultrasonic flow probe and a hydraulic vascular occluder. The dogs were studied under control conditions, after right stellectomy and after left stellectomy and after administration of propranolol and phentolamine. Right stellectomy did not affect RH. RH was significantly increased by left stellectomy from 476 ± 71% to 622 ± 86% (+31%) at the spontaneous heart rate and from 407 ± 51% to 577 ± 106% (+42%) during pacing. Propranolol significantly reduced RH from 447 ± 25% to 390 ± 27% (-13%) at the spontaneous heart rate and from 456 ± 25% to 311 ± 24% (-32%) during pacing. Phentolamine significantly increased RH from 419 ± 63% to 517 ± 71% (+23%). Propranolol was effective after bilateral stellectomy, whereas phentolamine was not effective after left stellectomy. In the second group of 14 anesthetized dogs with constant heart rate (15 (im) microspheres were injected twice into the left atrium. The first injection provided a control measurement; in nine dogs the second injection was made after left stellectomy. Left stellectomy significntly increased the left ventricular endocardial to epicardial ratio from 1.7 ± 0.03 to 1.23 ± 0.04. We conclude that the sympathetic nervous system has a tonic influence on coronary circulation and that left stellectomy increases the ability of the coronary bed to dilate and improves the endocardial perfusion.