Autoregulatory responses of cat mesenteric arterioles measured in vivo.

The purpose of these studies was to measure changes in the diameter of arterioles as large-artery pressure was varied. Changes in diameter were measured with a flying spot microscope in blood vessels of the mesentery of anesthetized cats. Arterial pressure was reduced in a single step and held at a constant level until the change in the diameter was complete. In experiments on 34 arterioles, 10 vessels showed a simple decrease in diameter as pressure was reduced; 24 showed a biphasic response. In the latter group the vessel narrowed for the first 5 to 15 seconds, but after this time an autoregulatory response occurred and the vessel dilated. In 12 of these vessels the diameter became larger in hypotension than it had been at normal arterial pressure. When pressure was suddenly restored, the vessel dilated further but returned to the control size as the autoregulatory response occurred. Analysis of the findings suggests that conditions of stability are satisfied in various portions of the pressure range. ADDITIONAL