Comparison of Fenestrations in Internal Elastic Laminae of Canine Thoracic and Abdominal Aortas

All non-elastin tissue was removed from canine aortas by placing them in 0.1 N NaOH at 75 degrees C for varying periods of time. The segments of aorta were weighed in a Mettler Chemical Balance at intervals. In 10 dogs the average weight of the thoracic aorta was 5.01 +/- 0.388 (SE) g while that of the abdominal aorta was 3.08 +/- 0.346 g. After digestion, the thoracic aorta weighed 3.34 +/- 0.0275 g and the abdominal aorta 0.85 +/- 0.085 g. Thus, the elastin makes up 67% of the thoracic aorta but only 28% of the abdominal aorta. These are equivalent to 0.334 g/kg body weight for the thoracic aorta and 0.224 g/kg body weight for the abdominal aorta. The values were always stable between 5 and 7 h and usually between 3 and 12 h. Aortic elastin was obtained from 5 dogs after 5-7 h of digestion and prepared for analysis by scanning electron microscopy. The dimensions of the fenestrations in the internal elastic laminae were quantified as described previously. The lower abdominal aorta had the largest holes (2.227 +/- 0.048 micron), and the upper thoracic aorta the smallest holes (0.954 +/- 0.032 micron). There was no significant difference in the size of the fenestrations along the thoracic aorta, but those in the lower abdominal aorta were larger than those in the upper abdominal aorta. The possible significance of the fenestrations in the genesis of aortic disease is discussed briefly.