³¹P NMR spectroscopy of perinatal hypoxic‐ischemic brain damage: A model to evaluate neuroprotective drugs in immature rats

Cerebral energy metabolism can be measured non‐invasively in unanesthetized neonatal rats with ³¹P NMR spectroscopy. Using this technique, serial changes in high energy phosphates were determined from the right cerebral hemispheres of 7 day postnatal rat pups during a hypoxic‐ischemic insult known to produce focal brain injury. During 3 h of hypoxia‐ischemia the concentration of ATP dropped to 33±8% of prehypoxic (baseline) levels, phosphocreatine (PCr)/P_i decreased from 1.5±0.51 to 0.16±0.06, while pH decreased nominally by 0.2 units. After 2.5 h of recovery in air, ATP returned to 75±10% of baseline levels, PCr/P_i rose to 1.1±0.28, and pH returned to its normal value of 7.16±0.06. This model was used to test the efficacy of the adenosine deaminase inhibitor, 2‐deoxycoformycin (DCF) as a potential neuroprotective drug. The data for the drug‐ and saline‐treated populations were analyzed by integrating ATP and P_i/PCr levels over specific time intervals, expressing it relative to baseline levels, and modeling it with cubic splines. Pretreatment with 500 μg/kg DCF shows a small, but statistically significant, preservation of both ATP and phosphorylation potential during hypoxia and initial recovery. Brain water content (edema) at 42 h recovery was apparently associated with both mean ATP and mean P_i/PCr in the last 2 h of hypoxia‐ischemia. When ATP fell below 70% of baseline, brain edema was evident at 42 h of recovery. This methodology is suitable for extension to human infants.