Arachidonic acid- and prostaglandin E2-induced cerebral vasodilation is mediated by carbon monoxide, independent of reactive oxygen species in piglets

Abstract

Arachidonic acid (AA) and prostaglandin (PG) E₂ stimulate carbon monoxide (CO) production, and AA metabolism is known to be associated with the generation of reactive oxygen species (ROS). This study was conducted to address the hypothesis that CO and/or ROS mediate cerebrovascular dilation in newborn pigs. Experiments were performed on anesthetized newborn pigs with closed cranial windows. Different concentrations of AA (10⁻⁸-10⁻⁶ M), PGE₂ (10⁻⁸-10⁻⁶ M), iloprost (10⁻⁸-10⁻⁶ M), and their vehicle (artificial cerebrospinal fluid) were given. Piglets with PGE₂ and iloprost received indomethacin (5 mg/kg iv) to inhibit cyclooxygenase. AA, PGE₂, and iloprost caused concentration-dependent increases in pial arteriolar diameter. The effects of both AA and PGE₂ in producing cerebral vascular dilation and associated CO production were blocked by the heme oxygenase inhibitor chromium mesoporphyrin (2 × 10⁻⁵ M), but not by the prostacyclin analog, iloprost. ROS inhibitor tempol (SOD mimetic) (1 × 10⁻⁵ M) and the H₂O₂ scavenger catalase (1,000 U/ml) also do not block these vasodilator effects of AA and PGE₂. Heme-l-lysinate-induced cerebrovascular dilation and CO production was blocked by chromium mesoporphyrin. Hypoxanthine plus xanthine oxidase, a combination that is known to generate ROS, caused pial arteriolar dilation and CO production that was inhibited by tempol and catalase. These data suggest that AA- and PGE₂-induced cerebral vascular dilation is mediated by CO, independent of ROS.