Effects of neural stimuli on blood flow through vasa vasorum in dogs.

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Abstract
The purpose of this study was to determine whether neural stimuli alter blood flow through vasa vasorum in the thoracic aorta. We measured flow with microspheres in anesthetized dogs and observed responses to sympathetic stimulation and baroreceptor stimulation. During these interventions, changes in arterial pressure were prevented with propranolol or an arterial reservoir, to minimize indirect effects on vasa vasorum mediated through changes in aortic wall tension. Electrical stimulation of the stellate ganglion at 10 Hz reduced blood flow to vasa vasorum in the thoracic aorta from 11 +/- 1.6 (mean +/- SE to 6.8 +/- 1.1 ml/min per 100 g (p less than 0.05). Aortic diameter, measured with a sonomicrometer technique, did not change during sympathetic stimulation. Thus, the reduction in blood flow through vasa vasorum during sympathetic stimulation appears to be a direct effect, and not the result of constriction of the aorta and compression of vasa. To determine effects of physiological alterations in neurogenic vasoconstrictor activity, we examined responses to stimulation of carotid baroreceptors. When pressure in isolated, perfused carotid sinus baroreceptors was raised from 81 +/- 3 to 198 +/- 2 mm Hg, blood flow to vasa vasorum of the thoracic aorta increased from 3.7 +/- 0.6 to 10 +/- 2.2 ml/min per 100 g (P less than 0.05). We conclude that vasa vasorum are responsive to neural stimuli, since they constrict during sympathetic stimulation and dilate in response to baroreceptor stimulation.