SYMPATHETIC CONTROL OF MAJOR CORONARY-ARTERY DIAMETER IN THE DOG

The diameter of a major coronary artery, the ramus interventricularis ventralis (RIV), was measured in dogs with arrested hearts perfused by an extracorporeal circulation. The resting diastolic diameter was 1.78 ± 0.07 mm (mean ± SE) at a diastolic pressure of 74.2 ± 3.4 mm Hg. Bilateral supramaximal stimulation of fibers leaving the cranial pole of the stellate ganglion decreased the diameter by 71.2 ± 8.9 μm, i.e., 4.0 ± 0.5% of the resting diameter. Stimulation of the left stellate ganglion contributed 59.8 ± 5.7% of the maximum response; that of the right contributed 40.3 ± 5.5%. Stimulation of the thoracic ganglia (T2-4) resulted in a 1.2 ± 0.4% decrease in coronary vessel diameter. RIV failed to respond to bilateral caudal cervical ganglion stimulation. After iv administration of phentolamine, 1-2 mg/kg, no response to sympathetic stimulation could be elicited. Therefore, it appears that α-receptors are activated by the release of the sympathetic neurotransmitter to sympathetic stimulation and that β-receptors are not involved in the response of RIV to sympathetic stimulation.