Blood Flow in the Aortic Wall

The indicator-fractiomition technic for measurement of regional blood flow has been applied to the measurement of blood flow in the aortic wall, using RbS(i. The aortic-indicator content declines slowly with time during the first minute, which shows that the aorta has a smaller extraction ratio for Rbsti than the rest of the body. The application of the indieator-fractionation teehnic when organ content of indicator changes with time is discussed. It is shown that the perfusion rate of rat aorta is at least 1.70 ml./Gm./min. This value is much larger than would be expected from in vitro studies of aortic oxygen utilization. ALTHOUGH the aorta is known to have awell developed system of vasa vasorum,1 its perfusion rate has not, to our knowl-edge, been measured. The technical diffi-culties involved in the application of ordinary methods of flow measurement, to the aortic wall are self-evident. A method recently de-veloped makes possible the measurement of blood flow to organs without discrete blood supply.- The present study is concerned with the application of this method to the meas-urement of the blood flow through the aortic wall. METHODS The methods were, with minor modifications, the same as those used before.2 Female rats of the Sprague-Dawley strain, weighing between 175 and 230 Gin. were anesthetized with sodium pentobar-bital (40 mg./Kg. I.P.) after an lS-hour fast, during which they were allowed free access to water. Five to 10 /xc. of RbSBCl in a volume of 0.2 ml. was injected into a femoral vein. The ani-mals were killed by transection through the thorax with a mallet-driven axe at 3.5-6, 10, 15, 20, 30, or 60 sec. after injection of the label. The aorta was taken from the aortic valves to the bifurcation of the iliacs. All branches were removed as close to their origin as possible. Adventitial tissue was stripped and the minute quantity of blood remain-ing in the aorta expressed. In 1 experiment, the aortas of eight rats killed at 10 sec. after label in