Summary
The aim of the investigation was to clarify the uptake of thrombin on vascular endothelium
and the inhibition of thrombin on the endothelium in the presence or absence of plasma.
Segments of porcine aorta were used. Thrombin was labelled with 125I and its enzymatic activity was assayed amidolytically using a specific chromogenic
substrate. After exposure to the endothelium both enzymatic activity and radioactivity
disappeared from the thrombin solution and were recovered as surface bound activities.
The enzyme activity confined to the endothelium rapidly disappeared in the presence
of plasma but no activity was recovered in the plasma. The surface confined radioactivity,
however, decreased slowly and was quantitatively recovered in the plasma. In the absence
of plasma, i. e. in the presence of a balanced Ringer’s solution, only slow disappearance
of thrombin enzymatic activity occurred although the rate of disappearance was higher
than that of release of radioactivity.
It is concluded that thrombin, taken up on the endothelium, is almost instantaneously
inhibited by an interaction mechanism with plasma and then released in an inactive
state. The endothelium itself, however, seems to slowly inhibit bound thrombin and
then release it.
Keywords
Endothelium - Thrombin - Inhibition
