Glutamine fasting state

Fig. 42.3. Interorgan amino acid exchange after an overnight fast. After an overnight fast (the postabsorptive state), the utilization of amino acids for protein synthesis, for fuels, and for the synthesis of essential functional compounds continues. The free amino acid pool is supported largely by net degradation of skeletal muscle protein. Glutamine and alanine serve as amino group carriers from skeletal muscle to other tissues. Glutamine brings NH4 to the kidney for the excretion of protons and serves as a fuel for the kidney, gut, and cells of the immune system. Alanine transfers amino groups from skeletal muscle, the kidney, and the gut to the liver, where they are converted to urea for excretion. The brain continues to use amino acids for neurotransmitter synthesis.

Amino acids are an important fuel for the intestinal mucosal cells after a protein-containing meal and in catabolic states such as fasting or surgical trauma (Fig. 42.13). During fasting, glutamine is one of the major amino acids used by the gut. The principal fates of glutamine carbon in the gut are oxidation to CO2 and conversion to the carbon... 

In these hypercatabolic states, skeletal muscle protein synthesis decreases, and protein degradation increases. Oxidation of BCAA is increased and glutamine production enhanced. Amino acid uptake is diminished. Cortisol is the major hormonal mediator of these responses, although certain cytokines may also have direct effects on skeletal muscle metabohsm. As occurs during fasting and metabolic acidosis, increased levels of cortisol stimulate ubiquitin-mediated proteolysis, induce the synthesis of glutamine synthetase, and enhance release of amino acids and glutamine from the muscle cells. 

A method for 3D MRSI has been demonstrated at 7T that utilises the Spectroscopic Missing Pulse - steady state free precession acquisition scheme. Modifications of previous implementations of the sequence at 3 T were required to comply with the limits of the specific absorption rate as well as to accommodate hardware limitations. The combination of two spatially selective radiofrequency pulses and a dual-band chemical shift selective radiofrequency pulse for simultaneous water and lipid suppression were used in fast 3D MRSI measurements in the brain of healthy volunteers. Signals from NAA, tCr, Cho, ml, and glutamate plus glutamine (Glx) were measured. ... 

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