The present study describes the relationships of extracellular striatal dopamine, cortical oxygen pressure, and striatal hydroxyl radicals in brain of newborn piglets during hypoxia and posthypoxic reoxygenation. Hypoxia was induced by reducing the fraction of inspired oxygen (FiO2) from 22% (control) to 7% for 1 h. The FiO2 was then returned to the control value and measurements were continued for 2 h. Cerebral oxygen pressure was measured by the oxygen dependent quenching of phosphorescence and extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and hydroxy radicals in the striatum were determined by in vivo microdialysis. Hypoxia decreased the cortical oxygen pressure from 47 +/- 2 to 9 +/- 1.3 torr (p < 0.001); the levels of extracellular dopamine in the striatum increased to 16,000 +/- 3,270% of control (p < 0.01), whereas the levels of DOPAC and HVA decreased to 25.3 +/- 6% (p < 0.001) and 36 +/- 5% (p < 0.01) of control, respectively. Compared with control, the hydroxyl radical levels at each time point were not significantly increased during hypoxia, although the sum of the measured values was significantly increased (p < 0.05). During the first 5 min after FiO2 was returned to 22%, the cortical oxygen pressure increased to control values and stayed at this level for the remainder of the measurement period. The extracellular level of dopamine declined to values not statistically different from control during 40 min of reoxygenation. During the first 10 min of reoxygenation, DOPAC and HVA further decreased and then began to slowly increase. By 70 min of reoxygenation, the values were not significantly different from control.(ABSTRACT TRUNCATED AT 250 WORDS)