Effect of Vasa Vasorum Flow on Structure and Function of the Aorta in Experimental Animals

Abstract

It is known that vasa vasorum flow contributes substantially to the nutrition of the outer layers of the thoracic aorta. This investigation was undertaken to test the hypothesis that impairment of vasa vasorum flow would alter the structure of the aortic wall and change the elastic properties of the aorta. The periaortic fat that contain the vasa vasorum for the ascending aorta was removed in seven anesthetized dogs, and the results were compared with those obtained from six weight-matched sham-operated control dogs. Aortic pressures, aortic diameters, and aortic distensibility were obtained before and 30 minutes and 15 days after removal of the periaortic vasa vasorum network. Aortic pressures were measured directly with a fluid-filled catheter. Aortic diameters were measured simultaneously with aortic pressures with an elastic, air-filled ring connected to a transducer. Aortic distensibility was calculated by the formula 2 x pulsatile change in aortic diameter/(diastolic aortic diameter x pulse pressure). Histology was performed in transverse blocks of aortic wall at the end of the experiment in both groups. The efficacy of the technique for the interruption of vasa vasorum blood supply to the aortic wall was demonstrated by histology in four additional animals that were killed without removal of vasa vasorum (two animals) and immediately after vasa vasorum removal (two animals). At baseline, heart rate, aortic pressures, aortic diameters, and aortic distensibility were similar in the two groups. A significant decrease in aortic distensibility was observed 30 minutes and 15 days after removal of the vasa vasorum in the experimental group (baseline, 3.453 +/- 1.023; 30 minutes, 2.521 +/- 0.760; 15 days, 1.586 +/- 0.488 10(-6).cm2.dyn-1; F = 9.532, P < .001). No changes were observed in aortic distensibility in the control group during the experiment. Histology of the aorta revealed medial necrosis, alterations of the elastin fibers, and a trend (P = .055) for altered collagen-to-elastin ratio in a region occupying more than the one (outer) half of the media of the experimental group animals. No changes were observed in the control group. The findings of the present study demonstrated that interruption of vasa vasorum flow led to an acute decrease in the distensibility of the ascending aorta. Moreover, structural changes of the aortic wall and further deterioration of the elastic properties of the aorta occurred 15 days after vasa vasorum removal.