[Early histoenzymologic and ultrastructural changes induced by adrenalin-thyroxine and fat diet in rabbit aorta...

The first stages of the atherosclerotic lesions induced in the rabbit aorta by adrenalin- thyroxine, with (or without) an hypercholesterolic diet, have been studied on the 6th, 13th, and 22nd day. Major parietal changes, barely demonstrable with light microscopic standard techniques, were detected, as soon as the 6th day, by electronmicroscopy and histoenzymology. These changes were probably due solely to the hormonal treatment. In the early stage, they consisted of some fragmentations of the elastic sheets and some smooth muscle cell lysis. The oxidative and ATPase activities were greatly reduced. The increased lysosomal hydrolase actitivities of the outer layers of the vessel could be related in the increased vascular permeability and consecutive increased perfusion gradient induced by these lesions. Later, an obvious repair process was seen. The smooth muscle cells bearing numerous processes were bound by many microfilaments and by some elastic material. The energetic enzymatic activities were increased. The part taken by the lipidic diet in these changes, apart from the increase of the esterase activity, did not seem yet of significance in this first stage of atherosclerosis. However, one cannot exclude that the intensively accumulating lipids might, at some later stages, potentiate the consequences of the vascular lesions or impede the repair process.