INCOMPLETE GLOBAL CEREBRAL-ISCHEMIA ALTERS PLATELET BIOLOGY IN NEONATAL AND ADULT SHEEP

Platelets are implicated as etiologic agents in cerebral ischemia and as modulators of neural injury following an ischemic insult. We examin ed the effects of severe, transient global ischemia on platelet aggreg ation during 45-min ischemia and 30-, 60-, and 120-min reperfusion in adult and neonatal lambs. We also examined postischemic platelet depos ition in brain and other tissues (120-min reperfusion) using indium-11 1-labeled platelets. Ischemic cerebral blood flow fell to 5 +/- 1 and 5 +/- 2 ml.min(-1).100 g(-1) in lambs and sheep, respectively. During ischemia, platelet counts fell to 47.5 +/- 5.1% of control (P < 0.05) in lambs and 59 +/- 4.9% of control in sheep (P < 0.05). Ischemia depr essed platelet aggregation response (P < 0.01) to 4 mu g collagen in l ambs and sheep (20.4 +/- 29.2 and 26 +/- 44.7% of control, respectivel y). Marked platelet deposition occurred in brain and spleen in sheep, whereas significant platelet entrapment occurred only in brain in lamb s. Our findings suggest that ischemia causes platelet activation and d eposition in brain and noncerebral tissues.