Ultrastructural changes in intraacinar pulmonary veins. Relationship to 3-methylindole-induced acute pulmonary edema and pulmonary arterial changes in cattle.

In 3-methylindole (3MI)-treated cattle electron-microscopic examination of intrapulmonary arteries showed changes of an arteritis which could be related to pulmonary hypertension. To further elaborate on this concept, the present study describes the ultrastructural pathology of intraacinar pulmonary veins in cattle 72 hours after oral administration of 3MI. The changes include significant thickening of the muscular pads of the media, massive glycogen accumulation in the venous smooth muscle cells, proliferation of the myointimal cells, focal protrusion of cytoplasmic portion of a smooth muscle cell into an adjacent cell body suggestive of vasoconstriction and emigration of lymphocytes and platelets through the vascular wall. The experimental data are discussed in relation to the ultrastructural pathology of intraacinar pulmonary arteries and acute pulmonary edema. The authors further present evidence that 3MI acute pneumotoxicosis is also associated with drastic vascular changes which may signify sudden elevation in arterial and venous pressures in the pulmonary system of cattle.