The plasma proteases, thrombin and plasmin, degrade the proteoglycan of rabbit aorta segments in vitro: an integrated ultrastructural and biochemical study.

The effects of plasmin and thrombin on the proteoglycan component of uninjured and deendothelialized rabbit thoracic aorta were examined in vitro. Aortas labelled with 35S in vivo, were exposed to each protease and the 35S-products released from the vessel were analysed. Aortas exposed to the same enzymes were examined by transmission electron microscopy of ruthenium red-stained sections, and the proteoglycan content evaluated by morphometric analysis. In uninjured vessels with endothelium intact, there was no evidence of release of proteoglycan by either enzyme unless very high concentrations were used. High concentrations of both plasmin and thrombin induced vacuolation of endothelial cells, and changes in the fine structure of smooth muscle cells. In contrast exposure of de-endothelialized vessels to smaller concentrations of plasmin or thrombin resulted in a significant loss of proteoglycan, and less marked changes in the morphology of the smooth muscle cells. Thrombin treatment released 35S-labelled products containing chondroitin-, dermatan- and heparan-sulphates whereas plasmin released products containing only chondroitin- and dermatan-sulphates together with other, unknown 35S-labelled products. These observations indicate the potential of non-specific, plasma-derived proteases to degrade arterial connective tissue.