Recent data suggested that platelet-activating factor (PAF) could play a pathophysiologically important role in the progression of hypoxic-ischemic brain injury. We investigated brain tissue PAF concentration in the hypoxic-ischemic brain of immature rats. Endogenous PAF concentration in brain tissue showed a marked increase in hypoxic-ischemic pups (Group 1, 85.6 +/- 15.5 pg/mg protein) when compared to that of the control (9.1 +/- 3.1 pg/mg protein). In addition, we studied the effects of pretreatment with L-carnitine (5 days and 2h before the hypoxia) on endogenous PAF concentration in the hypoxic-ischemic brain. Endogenous PAF concentration in the short-term pretreatment group (Group 2, 81.6 +/- 9.7 pg/mg protein) was not different than in Group 1 rat pups. However, a significantly decreased PAF concentration was found in the group of pups that received carnitine pretreatment for 5 days (Group 3, 30.5 +/- 11.0 pg/mg protein). These results indicate that PAF is an important mediator in the immature rat model of cerebral hypoxic-ischemic injury. The suppressor effect of L-carnitine on PAF production may give new insight into the treatment of hypoxic-ischemic brain injury.