Complexity of glutamine metabolism in kidney tubules from fed and fasted rats.

Glutamine is an important renal glucose precursor and energy provider. In order to advance our understanding of the underlying metabolic processes, we studied the metabolism of variously labelled [13C]glutamine and [14C]glutamine molecules and the effects of fasting in isolated rat renal proximal tubules. Absolute fluxes through the enzymes involved, including enzymes of four different cycles operating concomitantly, were assessed by combining mainly the 13C NMR data with an appropriate model of glutamine metabolism.