CELLULAR PATHOLOGY OF THE RAT AORTA - PSEUDO-VACUOLES AND MYO-ENDOTHELIAL HERNIAE

The aortic intima of adult rats, studied by electron microscopy, showed several changes indicative of spontaneous cellular pathology. These changes occurred almost exclusively at the level of fenestrae in the internal elastic membrane. The initial event was the formation of club-shaped cell processes arising from the smooth muscle cells and protruding into the fenestrae; this phenomenon gave rise to four types of images: (a) short pseudopodia reaching through the fenestrae; (b) long pseudopodia that pushed their way into the body of the overlying endothelial cells, giving rise to myo-endothelial herniae (reminiscent of the cell-to-cell herniae previously described in small, normal muscular arteries); (c) membrane-bound cellular parts apparently lying free beneath the endothelium, for which the current term ghost bodies in convenient; and (d) intraendothelial structures lined by two membranes, clearly arising through the mechanism of herniation, and best referred to as pseudo-vacuoles. Some of the myo-endothelial herniae become very large and stretch the endothelium to such an extent that it could easily burst, especially during tissue processing. This mechanism should account for many of the endothelial bulges and craters" often seen by scanning electron microscopy. The formation of such craters (arising from the collapse of myo-endothelial herniae as well as of endothelial blebs) offers a plausible explanation for the "stomata" and "stigmata" that have been described in silver nitrate preparations of the endothelium for over a century. © 1979 Springer-Verlag."