Effect of tissue plasminogen activator on intimal platelet accumulation in cerebral arteries after subarachnoid hemorrhage in cats.

Recombinant tissue plasminogen activator may be effective in preventing cerebral vasospasm after subarachnoid hemorrhage by resolving subarachnoid clots. We previously demonstrated that blood placed on the adventitial surface of cerebral arteries enhances intimal platelet accumulation, positively correlating with endothelial damage and other pathologic changes in vessel walls. In this study, we investigated the ability of a single bolus injection of tissue plasminogen activator to prevent platelet accumulation in cerebral vessels after subarachnoid hemorrhage. Subarachnoid hemorrhage was produced in cats by the transorbital intracisternal injection of 2.5 ml autologous arterial blood around the proximal part of the right middle cerebral artery. In 10 animals, 25 micrograms tissue plasminogen activator was injected at intervals of 10 (five cats) and 60 minutes (five cats) after subarachnoid hemorrhage. Intracisternal physiological saline (0.5 ml) was injected in six cats 10 minutes after subarachnoid hemorrhage. Platelets labeled with indium-111 were injected intravenously just before subarachnoid hemorrhage, and their radioactivity was measured in cerebral arteries at death. The results indicated that, after subarachnoid hemorrhage, early injection of tissue plasminogen activator inhibited intimal platelet accumulation, but later injection did not, although the extent of subarachnoid clot was reduced at both plasminogen injection times.