Brain lactate and pH dissociation in edema: 1H- and 31P-NMR in collagenase-induced hemorrhage in rats.

Brain edema has been shown to increase brain lactate, but the effect on pH is unclear. We used in vivo nuclear magnetic resonance (NMR) spectroscopy to measure lactate and pH in a region of brain edema. Ninety-five anesthetized rats underwent proton and 31P-NMR spectroscopy with a 7-T 89-mm vertical bore spectrometer, using a surface coil over the edematous regions and distant from a hemorrhage produced by the injection of bacterial collagenase. Brain water content was measured from multiple regions after the NMR measurements in all rats. Lactate was significantly increased 4 h after the hemorrhage and remained elevated for 48 h, but brain pH was unaffected. The increase in lactate correlated (P < 0.01) with the increase in water content in the measured region. We conclude that lactate and pH are dissociated in a region of primarily vasogenic edema.