Background and purpose: It has been suggested that recombinant tissue plasminogen activator (rtPA) may cause an aggravation of injury after transient focal ischemia via excitotoxic side effects. Such rtPA toxicity would be of major clinical significance since rtPA is increasingly used in stroke treatment. This study was conducted to evaluate the effects of dose, application time, and hemodynamic changes after intravenous rtPA treatment in focal ischemia.
Methods: Mice were subjected to a 90-minute episode of middle cerebral artery thread occlusion, and rtPA effects were assessed by laser-Doppler flowmetry, [(14)C]iodoantipyrine autoradiography, and triphenyltetrazolium chloride staining.
Results and conclusions: We provide evidence that rtPA provokes complex hemodynamic alterations in the ischemic brain tissue, which include an initial hyperperfusion and a more delayed hypoperfusion response. Changes are most pronounced in the periphery of the ischemic infarct, where regional blood flow drops below critical thresholds of tissue viability. Our observations suggest that changes of perfusion may at least partly explain the rtPA-induced increase of infarct size, which has previously been reported and which we also confirmed in the present experiments. Notably, both the secondary hypoperfusion and increase of infarct volume were abolished when rtPA-treated animals received additional heparin infusions. This finding suggests that a secondary hypercoagulability may compromise brain perfusion after rtPA delivery. Accordingly, early treatment with heparin might help to prevent the rtPA-induced changes.