Thrombosis induced in vivo in the femoral artery of rats. An electron microscopic study of myointimal growth.

Minor injury and thrombosis, induced in a short arterial segment by the successive applications of a weak electric current and a dilute solution of ADP, is followed by rapid reconstitution of the endothelium and protracted growth of the medial smooth-muscle cells (SMC). Previous investigations of their early stages have shown that both processes are platelet-dependent. In the present investigation the arterial-wall reaction was followed up to the eighth day. By that time the growth of SMC had abated and the artery wall had regained a normal structure. Locally repeating the electric treatment consistently caused an infiltration of the inner media by blood elements, notably platelets. Rupture of the lamina elastica interna (LEI) was an additional feature in one out of 6 repeatedly treated arteries. Despite greater initial damage, repair of the artery wall proceeded normally in the majority of cases. In 2 out of 7 arteries, however, the SMC of the inner media exhibited cytologic evidence of still active stimulation and disordered growth on the eighth day. In one of the 2 arteries, the LEI had ruptured over wide areas where myointimal thickening was observed. Intimal denudation was brief in all cases so that the release of mitogenic factors by insudated platelets and the disruption of the LEI are more likely to have been the effective agents of myointimal growth.