31P-NMR studies on the energy metabolism of the living rat brain using a surface coil method

We have examined the changes of the energetic metabolic state of rat and mouse brains under hypoxic hypoxia or ischemia using a 31P-NMR spectrometer with a surface coil. The NMR spectrometer has a super-conducting magnet providing a homogeneous magnetic field of 6.3 tesla. A probe was remodelled to accommodate an experimental animal in it. The animals were anesthetized with 1.0% or 1.5% halothane throughout the experiments. The optimal measurement conditions were a 90 degrees pulse width of 20 microsecond, and a 2 sec pulse repetition time. 200 acquisitions of FIDs was required for high spatially resolved signals. The Pcr/ATP ratio of the live, anesthetized rat brains was 1.76 +/- 0.46 (n = 8) for cerebra and 1.63 +/- 0.11 (n = 4) for cerebella. That of gerbil brains was 1.23 +/- 0.09 (n = 4). The Pcr/ATP ratio did not show any significant changes under both the conditions of hypoxic hypoxia or ischemia. The value of Pcr/Pi ratio decreased in the hypoxic conditions. The level of Pcr. of rat cerebrum decreased by 76.8 +/- 10.5% at 10% oxygen and by 57.3 +/- 15.7% at 5% oxygen compared with the value of 20% oxygen. The ATP level in the rat brain also decreased according to the degree of hypoxia. Cerebral ischemia was produced in the gerbil by ligation of the common carotid artery. The levels of Pcr. and ATP were severely depressed in the ischemic hemisphere but those of the intact side remained normal.