The Effect of Glucose on the Oxygen Supply of the Blood-Free Perfused Guinea Pig Brain as Measured by Reflection Spectra and Po2 Histograms
Earlier experiments with the guinea pig brain had shown that at a temperature of 37° with a substrate-free macrodex solution, equilibrated with 95% O2 and 5% CO2 and with a large flow cytochrome aa3 (cyt aa3) was only about 60% oxidized (Schwickardi, 1968; Heinrich et al., 1981). Under similar conditions the heart muscle behaves differently: In the blood-free perfused Langendorff heart the cyt aa3 is about 95% oxidized (Figulla et al., 1979). Since in this case the perfusion medium was different, the question arises, whether the difference in the composition of the perfusion medium (for example the addition of substrate) influences the oxygen supply and can — at least in part — be responsible for the observed difference in the redox state of the respiratory chain. To have a better insight in the oxygen supply, in the following experiments, we combined the measurements of the redox states of the cytochromes with the measurements of Po2 histograms on the brain surface. The redox state of cytochrome aa3 serves as an indicator of the intracellular mitochondrial O2 supply, whereas the Po2 histogram indicates the Po2 distribution in the extracellular space. The measurements were performed with two different perfusion media and at two different temperatures.
KeywordsRedox State Reflection Spectrum Oxygen Supply Brain Cortex Perfuse Brain
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