Platelet Embolism in Rabbit Brain 781

SUMMARY Transient cerebral ischemia was induced in rabbits by sdectire infusion of arachldonlc add (0J5 mg/kg in 15 sec) into the internal carotid artery. Platelet emboll caused transient ischemia of the brain, reaching a maximum within a few seconds after injection. After embolism the EEG flattened, blood flow stopped in almost tbe entire injected hemisphere, cortical pH gradually fell from 731 ± 0.09 to 7.05 ± 0.10 and cortical K+ actirity rose from 4.7 ± 1.8 to 12.7 ± 6.4 mmol/kg H,O. Complete ischemia lasted 3-5 min; then cerebral circulation was gradually restored without reactire hyperemia. Forty-fire mm after emboliza-tion, circulation had been resumed in almost the entire Injected hemisphere, whereas metabolic changes were still disturbed. Eighty percent of the animals recorered complete neurological function and 20 % showed per-manent damage confirmed by hlstologlcal examination after 1 week of recorery. Stroke,Voll2,No6,1981 SEVERAL INVESTIGATIONS have given evidence that the brain has a capacity to recover both meta-bolic and neurophysiological functions following an extremely long period of ischemia.1" * In contrast, clinical experience as well as a number of experi-mental studies have shown that following, for exam-ple, cardiac arrest, signs of irreversible brain damage may develop even if the primary ischemia only lasts a few minutes.9 The ultimate recovery of the brain following transient ischemia is not only dependent on the duration and intensity of the ischemia, but also on pathophysiological events during post-ischemia. To interpret the mechanisms responsible for the final sequelae of ischemia, clarification of early meta-bolic and functional alterations in affected brain tissue is of considerable importance. One type of cerebral ischemia of clinical importance is focal cerebral transient attacks (TIA) because they indicate increased risk for subsequent development of cerebral infarction. In the present series of experi-ments we have studied the changes in regional cere-bral blood flow (rCBF) and metabolism in the rabbit brain during the post-ischemic period following a transient ischemic attack mimicked by producing in-travascular platelet aggregates with selective intra-carotid injection of arachidonic acid