Ultrastructural pathology of intrapulmonary arteries in 3-methylindole-induced pneumotoxicity in cattle: II. Glycogen accumulation in the smooth muscle cells and intimal changes.

3-Methylindole (3MI) was orally administered as a single dose of 0.1-0.2 g/kg which then produced acute pulmonary oedema in cattle 72 h post-treatment. Electron microscopic examination of intrapulmonary arteries ranging between 35-120 microns in the control animals, revealed microsequestration of rough endoplasmic reticulum (RER) and the storage of proteinaceous material in the dilated cisternae of RER of the endothelial cells. Lung tissue samples collected after 72 h of 3MI administration, showed denudation and hyperplasia of the endothelial cells. Massive storage of glycogen particles and the lamellar bodies in association with glycogen, were observed in the smooth muscle cells of the media. The importance of glycogen accumulation in vascular smooth muscle cells of the pulmonary arteries is discussed in terms of energy utilization and vascular energetics to meet the metabolic requirement of haemodynamic stress arising from alveolar hypoxia and possible vasoconstriction. Furthermore, the suggestion is made, that the alterations may signify the early changes of pulmonary hypertension induced by the toxic effect of 3MI in cattle.