Hypoxic brain injury is the most important neurological problem during the perinatal period. However, lack of information on cerebral blood flow (CBF) and its regulation in the postnatal period has prevented clear understanding of the pathogenesis of this condition. The overall goal of this proposal is to gain insight into the metabolic regulation of CBF in the postnatal period and to define the role of adenosine in linking brain metabolism and CBF at this developmental stage. Our specific aims are 1) to investigate whether exogenous adenosine produces cerebral vasodilation and increase in CBF in the newborn; 2) to examine the role of adenosine in vasodilatory response to photic stimulation in the neonatal brain; 3) to determine if the adenosine level rises to produce vasodilation in the neonatal brain during hypoxia; 4) to determine the effect of systemic hypotension on the regional brain adenosine level and the role of adenosine in selective sparing of gray matter flow during severe systemic hypotension in the newborn. CBF will be measured by the radioactive microsphere technique. The brain microdialysis technique will be employed in detecting the interstitial fluid adenosine level. Adenine nucleosides and nucleotides will be measured by HPLC techniques.