Reaction of pial arteries and veins to sympathetic stimulation in the cat.

The diameters of pial arteries and veins were continuously monitored by a multichannel videoangiometer through a closed cranial window in 13 cats. Seventy-two arterial portions (diameter 30-283 micrometer) and 103 venous segments (diameter 32-486 micrometer) were studied under resting conditions and during stimulation of the cervical sympathetic chain. Arteries with a diameter of less than or equal to 150 micrometer constricted 7.3 +/- 0.8%; those greater than 150 micrometer 13.1 +/- 1.4% (p less than or equal to 0.0005 for both groups). Veins constricted significantly more than arteries of corresponding size (p less than 0.005). Veins less than or equal to 150 micrometer constricted 11.5 +/- 0.9% and those greater than or equal to 150 micrometer constricted 19.9 +/- 1.9% (p less than 0.0005 for both groups compared to resting levels). Since the venous compartment contains about 70% of the regional blood volume the tone of the veins is of importance for intracranial pressure. Further studies on the role of sympathetic nervous activity in the regulation of cerebral venous tone under physiological and pathological conditions seem essential.