Cerebral sodium extraction in the dog: a test for extracerebral contamination.

The single-pass extraction of sodium was measured with and without sympathetic stimulation in dogs anesthetized with alpha-chloralose. A mixture of the test (24Na) and reference ([125I]RISA) substances was injected as a bolus into the common carotid artery. Single-drop samples were taken at approximately 1-s intervals from the sagittal sinus and the temporal sinus while cerebral blood flow was continuously measured at the temporal sinus by the venous outflow technique. The extraction measurements were used to test for extracerebral contamination of venous outflow. The mean integral extraction determined from sagittal sinus samples was 2.2% during control conditions and 3.0% during sympathetic stimulation. The mean temporal sinus extraction of sodium was 6.9% during control and 2.7% during sympathetic stimulation. If true cerebral sodium extraction is assumed to be 1.4% and extracerebral sodium extraction is 60%, then these data indicate that extracerebral contamination is less than 10%.