Endogenous platelet activating factor does not modulate blood flow and metabolism in normal rat brain.

Both platelet activating factor and eicosanoids participate in the cerebrovascular response to ischemia. Eicosanoids also modulate cerebrovascular tone under normal physiologic circumstances, but a similar role for platelet activating factor has not been investigated. Therefore, using 16 rats, we studied the effects of the platelet activating factor receptor blockers BN 52021 (10 mg/kg, n = 4 or 30 mg/kg, n = 2) and WEB 2086 (5 mg/kg, n = 6) on global cerebral blood flow and the cerebral metabolic rate for oxygen and compared them with the effect of indomethacin (10 mg/kg, n = 4). Neither antagonist altered cerebral blood flow (112 +/- 16 and 107 +/- 14 ml/100 g/min at baseline versus 108 +/- 16 and 105 +/- 18 ml/100 g/min after BN 52021 and WEB 2086, respectively). In contrast, indomethacin significantly (p less than 0.05) decreased cerebral blood flow from 106 +/- 8 to 69 +/- 4 ml/100 g/min. No treatment altered the cerebral metabolic rate for oxygen compared with baseline. These data suggest that in normal rat brain, concentrations of platelet activating factor, unlike those of eicosanoids, are subthreshold and do not modulate cerebral blood flow or the cerebral metabolic rate for oxygen.