Role of elastase and lysyl oxidase activity in spontaneous rupture of internal elastic lamina in rats.

Rupture of the internal elastic lamina may occur spontaneously with age in certain arteries of the rat and to various extents in different strains. This phenomenon may have some bearing on certain aspects of arterial pathology. For this study, we investigated biochemically the mechanisms of formation of interruptions in the internal elastic lamina (IIEL) by comparing aortas of Brown Norway (BN) rats, which develop numerous IIEL in the abdominal aorta, with those of Long-Evans (LE) rats, which develop none. We isolated aortic elastin from BN and LE rats and determined its amino acid composition and its susceptibility to different elastases. No differences were found between the two strains, but the quantity of elastin isolated per aorta was lower in the BN than in the LE rats. Elastase-like activity (ELA) of whole aortic extracts, measured with Suc(Ala)3NA as a substrate, was greater in the BN rats than in the LE rats of both sexes. The assay of ELA in endothelium, media, and adventitia extracted separately showed very low levels in the media compared to the endothelium and adventitia. The endothelium accounts for about one-half of the total aortic ELA, but a difference between the two strains was detected only in the adventitia. With 3H-insoluble elastins prepared from BN and LE aortas as substrates, elastinolytic activity (EA) was detected only in extracts of endothelium after prior exposure to trypsin. Extracts from BN endothelium on BN elastin were more active than were those from LE endothelium on LE elastin. The assay of lysyl oxidase activity in aortic extracts from the two strains with 3H-collagen from chick embryo calvaria as the substrate showed a lower activity in the BN than in the LE rats. Taken together, these results suggest that increased elastase activity and decreased lysyl oxidase activity may be involved in the formation of IIEL.