Increased platelet-activating factor-induced periventricular brain microvascular constriction associated with immaturity.

Oxidant stress contributes to the pathogenesis of hypoxic-ischemic encephalopathies. Platelet-activating factor (PAF) is generated during oxidant stress. We studied the vasomotor mode of actions of PAF on periventricular (PV) microvessels of fetal (≈75% of term), newborn (1–3 days), and adult pigs. PAF constricted PV microvessels from fetal (29.27 ± 2.6%) and newborn (22.14 ± 3.2%) pigs but was ineffective in adults ( newborn>adult profile. Thus the greater PAF-induced PV microvascular constriction in younger subjects seems attributable to greater PAF receptor density and mostly secondary to TXA2 formation from endothelium. The resulting decrease in blood flow may contribute to the increased vulnerability of the PV brain regions to oxidant stress-induced injury in immature subjects.