Brain high energy phosphate responses to alcohol exposure in neonatal rats: An in vivo P-31-NMR study

Background: The mechanisms that mediate fetal brain injury which results fr om maternal alcohol consumption are not well understood. Although fetal hyp oxia is a popularly proposed mechanism, it has been difficult to assess bra in oxygenation in vivo. We measured intracellular high energy phosphate con centrations and estimated intracellular pH (pH,) in brains of unanesthetize d neonatal rat pups by using in vivo P-31-NMR spectroscopy. We reasoned tha t decreases in brain oxygenation sufficient to result in brain injury would also reduce high energy phosphates and pH(i). Methods: On postnatal day 4, before alcohol administration, pups were place d into a 20 mm diameter NMR probe, their heads were positioned carefully in the center of the P-31 detection coil, and spectra were collected over 20 min. Animals were then fed diet with or without 4.5 g/kg of ethanol in two tin succession) of 12 daily feedings via artificial rearing methods. A seco nd spectrum was collected at 90 min after the beginning of the second alcoh ol feeding, at the time that coincided with the peak blood alcohol concentr ation (BAC). Identical feedings were performed daily until day 9, when pre- and postfeeding spectra were again obtained. Positive control groups were fed control diet and were studied in atmospheres of 5% oxygen, 95% nitrogen or 0% oxygen, 100% nitrogen. Results: Phosphocreatine (PCr), beta-adenosine triphosphate (ATP), and pH(i ) decreased and inorganic phosphate (P-i) increased in day 4 animals subjec ted to 0% oxygen (20 min) compared with pretreatment and all other treatmen t groups. Day 9 animals did not tolerate these conditions. There were no si gnificant changes in response to 5% oxygen on day 4, but P-i increased and beta-ATP decreased compared with pretreatment values and compared with alco hol and control groups on day 9. There were no changes in PCr, beta-ATP, or pH(i) in response to alcohol treatment at either age. PCr was significantl y increased in the alcohol and 5% oxygen groups and apparently increased in the control group on day 9 compared with day 4, most likely due to increas es in cranial muscle mass within the NMR coil. Conclusions: We conclude that acute alcohol exposure that results in peak B ACs of 315 mg/dl does not alter brain high energy phosphate concentrations or pHi in neonatal rat pups, although these BACs are known to result in sig nificant brain injury. These findings do not support hypoxia as a mechanism of alcohol-mediated brain injury during the third trimester equivalent in the rat pup model.