No abstract

A B S T R A C T Lysis of fibrin in tissue culture has been shown to be due to plasminogen activator identified immunologically as urokinase. The present study examines fibrinolytic events in culture, particularly mechanisms leading to increased urokinase levels and accelerated fibrinolysis.Deposition of fibrin on cells in culture was followed by a two-to six-fold increase in urokinase in the supernates and rapid disappearance of the fibrin. Investigation of factors that might be responsible for these events (including fibrin, fibrinogen, vasoactive stimuli, and the enzymes thrombin and plasmin) indicated that the enhanced urokinase yields were mediated through plasmin and thrombin.Study of the possible modes of action of thrombin and plasmin indicated that these enzymes are capable of acting on the cells themselves as well as on cell-produced material. The effect on cells was manifested by mitotic activity or, occasionally, cell injury and death. Although these effects influenced urokinase levels, enhanced yields were explained best by the action of enzymes on cellproduced material. Studies with plasmin and thrombin, and also trypsin, indicated that proteolytic enzymes may act in various ways-affect the stability of urokinase, interfere with inhibition of urokinase by naturally occurring inhibitor(s), and induce urokinase activity from inactive material. Plasma and thrombin appeared to act primarily through the latter mechanism.Inactive material, which gave rise to urokinase upon exposure to proteolytic enzymes and which may represent urokinase precursor, was found in cultures of kidney, lung, spleen, and thyroid. Urokinase in such inactive state appears to be readily accessible to activation by enzymes, particularly plasmin and thrombin, thus Abstract of preliminary results appeared in 1970 Clin. Res. 18: 398.

Glomeruli from normal and diseased human kidneys were explanted in tissue culture chambers and were studied by phase-contrast microscopy and time-lapse cinematography. Observation from the time of explantation to several months of culture revealed that glomerular cells are capable of prolonged survival and various activities in vitro. Glomerular cells retained in culture some of the morphological and functional characteristics described in fixed preparations and revealed, in addition, dynamic aspects peculiar to living cells. Cells lining glomerular capillary loops exhibited pulsatile movements which caused glomeruli to contract and expand rhythmically. Persistent, rhythmic and synchronous contractions of entire glomeruli were dependent upon the presence of viable, grossly intact pulsatile cells in all capillary loops. This activity was impaired or lost through injury or death of cells.

Summary. Plasma fibrinogen and its degradation products (FDP) were examined in mice given single injections of Ancrod, the purified coagulative fraction of Malayan pit viper venom previously called Arvin. Clottable fibrinogen had disappeared completely 5 min after the injection and slowly reappeared 12 hr later. At least 2 FDP appeared in the plasma 30 min after the injections while 5 hr later only one FDP was present which corresponded to human fragment E. This was in contrast to in vitro lysis of mouse fibrinogen which yielded two late FDP corresponding to human fragments D and E. The fibrinolytic system also was examined in the plasma of these animals. 30 min after the injection, plasminogen was decreased in amount but increased in susceptibility to activation by urokinase. Transient, modest increases in fibrinolytic activity were evident in diluted plasma samples 1 hr and again 8 hr after the injections. Inhibitors of fibrinolysis did not differ from those in normal mice. These observations are correlated with our previous immunofluorescent and histochemical studies on these and other animals. The present data support our earlier conclusion that fibrinolysis within small vessels of the tissues is of major importance in the reaction to Ancrod.

No abstract