Experimental aortitis. Aortic lesions induced by a serine protease.

The etiology of aortitis syndrome (Takayasu's arteritis) is unknown. This study was designed to show whether aortic and pulmonary artery lesions might be induced by a small dose of protease in the circulating blood of rabbits. Serum trypsin activity was increased transiently but significantly by an intravenous infusion of the enzyme at the rate of 1000 IU/min for 100 min. The aortic wall was significantly thickened. Marked edema and focal tears were seen in the intima and media and a mild inflammatory reaction in the adventitia of rabbits sacrificed 2 weeks following trypsin infusion. The lesions were also present in rabbits sacrificed at 6 weeks. They were observed in 7 of 8 rabbits given the same dose of chymotrypsin-A4, but not in control rabbits infused with saline alone. The lesions were observed frequently in the ascending aorta and arch, but were rare in the descending aorta. The main pulmonary artery showed similar lesions in about half of the studied rabbits. These results show evidence that a diffuse lesion of the aorta and pulmonary artery may be induced by a small dose of serine protease in the circulating blood.