Laser beam - induced injury of aortae of arteriosclerotic and nonarteriosclerotic rats.

The abdominal aortae of non-arteriosclerotic (virgin) and arteriosclerotic (breeder) Sprague-Dawley rats were exposed by laparotomy and a microscopically discreet locus within the inner media was subjected to non-thermal injury by a pulsed ruby laser beam (300 joules/cm2). Animals were killed every two days for 8 days. The non-arteriosclerotic rats manifested increased mesenchymal cell activity at the site of injury followed by intimal ground substance accumulation populated by mesenchymal cells and culminating with medial scarring with extensive loss of elastic lamellae. The arterioscelrotic aortae displayed no medial mesenchymal cell reaction but immediately below the lesion site there was active differentiation of intimal mesenchymal cells into cartilaginous cells and eventual transformation of both the intima and media into large C-shaped bars of cartilaginous tissue. It is believed that laser beam injury accelerated the differentiation of the already disturbed mesenchymal cells of the arteriosclerotic animals in the direction of mature cartilage to strengthen a weakened aortic wall.