Simultaneous Localized in vivo 1H and 15N MRS of Glutamine Synthesis in the hyperammonaemic rat brain

An alternative approach to 13C MRS for studying glutamate and glutamine metabolism is 15N MRS during infusion of 15N labeled ammonia. Ammonia is metabolized to glutamine by glutamine synthetase (GS) in astrocytes. Consequently, the activity of cerebral glutamine synthetase in vivo under hyperammonaemia conditions may help understand the mechanism of ammonia toxicity and could provide further insight into the Gln-Glu cycle. Previous NMR studies on cerebral GS under ammonia infusion used either in vivo 1H or unlocalized 15N spectroscopy (1-3) and all used in vitro brain extracts for absolute quantification. Therefore, the goal of this study was to use i