[Experimental studies on proteolysis of hyaline membranes in vitro (author's transl)]

The incubation of lung tissue from premature infants with pulmonary hyaline membranes in fibrinolysis activating or fibrinolytically active solutions gave the following results. With streptokinase it was not possible to dissolve hyaline membranes (verification of the physiological lack of plasminogen in premature infants). The mean content of membranes after 24 hours showed to be 18.14 +/- 12.43% which almost corresponded to the control value of 20.24 +/- 10.54% after incubation in NaCl-solution. In comparison, solutions of plasmin, plasmin-activator or activator prepared from proactivator-plasminogen through activation with streptokinase led to a clear reduction in the membrane content, i.e. 11.00 +/- 6.50, 13.89 +/- 9.72, and 13.63 +/- 8.94%, respectively. A decrease in membranes equally strong to that after plasmin appeared after incubation for only 12 hours in trypsin (11.09 +/- 8.62%). Plasmin, plasmin-activator, and activator, but not streptokinase alone, caused also a considerable nonspecific proteolysis of the lung parenchyma which was equal to the trypsin effect, for example, with an only half as long incubation time. Since the lungs of premature infants contain the tissue activator of fibrinolysis we discuss the suggestion of Ambrus et al. (1974) to administer an injection of plasminogen to premature infants immediately after birth so that a spontaneous fibrinolysis can be favoured for developing hyaline membranes.