Summary
Neurotoxic effects of endogenous tissue plasminogen activator (tPA) have recently
been reported. Employing a rat model of thromboembolic stroke, we evaluated the extent
and degree of extravasation of exogenous tPA administered for the purpose of fibrinolysis.
In a thromboembolic model using Sprague-Dawley rats, focal cerebral ischemia was induced
at the territory of the middle cerebral artery (MCA). Early reperfusion was induced
by administering tPA (10 mg/kg) intravenously at 30 minutes after the onset of ischemia.
Extravasated tPA was evaluated by immunohistochemistry, and the concentration of tPA
in the brain tissue was quantified by enzyme-linked immunosorbent assay methods. The
integrity of the blood-brain barrier (BBB) was examined electronmicroscopically. In
a thread model of transient ischemia, reperfusion was induced without tPA adminis-tration
at 30 minutes or 2 hours after the onset of ischemia, and the tPA content of the brain
was quantified. In the rats with thromboembolic stroke, extravasation of tPA was observed
at the territory of the MCA. Both the endogenous and exogenous tPA contents were 3.5±1.6
ng/ml of homogenized brain in saline. Electronmicroscopically, mild ischemic changes
were observed, although the integrity of the BBB was preserved. In the thread model
rats, the endogenous tPA contents of the ischemic hemisphere were 0.9±0.1 and 1.0±0.2
ng/ml in the 30-minute and 2-hour ischemia groups, respectively, and were significantly
lower than the tPA contents in the thromboembolic stroke rats (p < 0.01). The present
findings indicate that significant extravasation of exogenous tPA occurs through the
cerebral vessels even though early reperfusion is induced.
Keywords
Extravasation - fibrinolysis - rat - thromboembolic stroke - tissue plasminogen activator