1. The effects of electrical stimulation of the distal ends of cut preganglionic cervical sympathetic trunks and cut sinus nerves on carotid body total blood flow, local blood flow and tissue PO2 (Pt,O2) were studied in anaesthetized cats. 2. Sympathetic stimulation caused reductions, often marked, of the total blood flow through the carotid body, yet did not influence local flow or Pt,O2 recorded by electrodes whose tips lay in deep locations within the carotid body. Intraglomeral electrodes did respond to reductions of perfusion pressure and to perfusions of the carotid body with saline solutions. 3. Values of Pt,O2 recorded from superficial tissues of the carotid body were higher than those from deeper locations and were increased by blowing oxygen over the surface of the organ. In these locations, sympathetic stimulation increased Pt,O2. 4. An increase in the frequency of sinus nerve chemosensory discharges during sympathetic stimulation was obtained in the presence of an unchanged Pt,O2 recorded from deep glomeral locations. 5. Stimulation of the distal end of the sinus nerve increased the total blood flow through the carotid body but did not affect local flow or Pt,O2 recorded from deep glomeral locations. 6. It is concluded that autonomic nerves supplying the carotid body mainly influence arteriovenous anastomotic and/or other shunt vessels, with little control being exerted on vessels regulating the flow through the capillary network of the specific tissue. This investigation also indicates that the flow in the capillary network of the specific tissue is a small proportion of the total flow. Support is given to the view that autonomic nerves can influence chemoreceptor activity by non-vascular mechanisms.
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