Intestinal O2 uptake during sympathetic stimulation and partial arterial occlusion

Publisher Website
Google Scholar
Abstract
In isolated loops of canine small bowel perfused at constant blood flow, stimulating perivascular sympathetic nerves (8-10 Hz) depressed O2 extraction and O2 uptake. Because sympathetic stimulation also decreased 86Rb extraction, sympathetic stimulation appears to close precapillary sphincters and through diffusion limitations reduces the capillary-to-cell flux of oxygen. To determine if sympathetic stimulation could lower O2 uptake under more physiologic circumstances, a 2nd series of experiments was performed during constant arterial pressure perfusion. Sympathetic stimulation reduced blood flow by about 30% in the steady phase. Oxygen extraction did not increase appreciably, so O2 uptake was also reduced. When partial arterial occlusion was used to lower the blood flow to the level that it reached during sympathetic stimulation, large increases (37%) in O2 extraction occurred so that O2 uptake remained near control levels. After arterial occlusion local mechanisms maintain O2 uptake by increasing O2 extraction through capillary density increases, but this mechanism is impaired by sympathetic stimulation.