Are enlarged fenestrations in the internal elastic lamina of the rabbit thoracic aorta associated with poststenotic dilatation?

A stenosis amounting to 45-60% of the luminal diameter was made in the thoracic aorta of six New Zealand White rabbits. The progress of the ensuing poststenotic dilatation (PSD) was followed by daily X-ray analysis after which angiograms were taken for the calculation of luminal diameters. Specimens of the aorta proximal and distal (PSD) to the stenosis were digested to expose the internal elastic lamina (IEL) and viewed using a scanning electron microscope. The dilatations, which ranged between 7 and 30% reached their maximum diameter after only 8-10 days. The average diameter of the fenestrations distal (2.30 +/- 0.53 SEM) to the stenosis were significantly larger (p less than 0.01) than proximal (1.33 +/- 0.16 SEM) and covered a significantly larger (p less than 0.005) percent of the surface area of the IEL. It is suggested that the enlarged fenestrations may result in changes to the mechanical properties of the IEL which would play an important role in the genesis of PSDs.