A comparison of the orientation of elastin fibers in the elastic laminae of the pulmonary trunk and aorta of rabbits using the scanning electron microscope.

Five pulmonary trunks and two aortas from adult rabbits were fixed in formalin as close to their in vivo dimensions as possible. They were then cut open, pinned out, stripped to expose their medical elastic laminae, dehydrated, and coated with gold. A hair was placed over each specimen as a reference line for orientation purposes. The arteries were examined under a scanning electron microscope and 20 photographs were taken of each specimen. The tangential surface of an elastic lamina was seen to consist of long, parallel, anastomosing, broad elastin fibers with numerous finer fibrils interconnecting them at right angles. The angle which each elastin fiber made with the circumferential axis of the vessel was measured. Although elastin fibers within any particular level within the media were all roughly parallel, there was variation in orientation of fibers between successive elastic laminae. This variation was relatively slight in the aorta where most fibers were approximately circumferentially orientated. In the pulmonary trunk the variation in orientation was extreme and extended completely over a 180 degree range.