The electron microscopy of "fibrinoid necrosis" in pulmonary arteries.

Fibrinoid necrosis was induced in the pulmonary arteries of five male Wistar albino rats by feeding them on a diet adulterated by the addition of 0.07% ground Crotalaria spectabilis seeds by weight. Electron microscopy of the arteries affected by the process showed fibrin in the thrombus occluding their lumens and in the arterial intima, held up from further penetration of the media by the inner elastic lamina. Naturally occurring gaps in this lamina were found, and it is postulated that they determine the characteristic histological configuration of fibrinous vasculosis. The smooth muscle cells of the media of the pulmonary veins showed clear evaginations, devoid of myofilaments and organells, indicative of sustained constriction compatible with viability of the cells. In contrast, the smooth muscle cells of the media of the pulmonary arteries showed loss of myofilaments leading to frank necrosis. Other cells seen in the media include fibrocytes and "vasoformative reserve cells." The authors consider that the latter have considerable and varied potential. Once liberated during the process of fibrinoid necrosis in the arterial media they may play an important part in pulmonary vascular pathology as, for example, in the formation of the plexiform lesion.