Proteolytic Capacity in Human Plasma Part I Measurement of proteolytic activity in the presence of natural inhibitors and study of the inter-individual variations

The maximal proteolytic activity in plasma that can be obtained by activation with urokinase and in the presence of natural inhibitors is designated proteolytic capacity. A modified caseinolytic method measuring this parameter has been described. In a normal population large variations between individuals were found, and this is probably due to differences in the plasminogen-plasmin level. The caseinolytic method correlated well with in vitro thrombolysis and with fibrinogenolysis in plasma. Serum had a higher proteolytic capacity than plasma. Pregnancy and the oral contraceptives caused a pronounced rise in proteolytic capacity, whereas thyrotoxicosis caused a decrease in the capacity. Two healthy donors, one with zero proteolytic capacity and a plasminogen level of 35–45%, and one with very high proteolytic capacity and a plasminogen level of about 130% were studied in particular. No increased tendency for thrombosis was found in persons with very low or zero proteolytic capacity.