Glutamine and glutamate metabolism across the liver sinusoid

The liver shows net glutamine uptake after a protein-containing meal, durin g uncontrolled diabetes, sepsis and short-term starvation, but changes to n et release during long-term starvation and metabolic acidosis. Some studies report a small net release of glutamate by the liver. The differential exp ression of glutamine synthetase (perivenous) and glutaminase (periportal) w ithin the liver indicates that glutamine is used for urea synthesis in peri portal cells, whereas glutamine synthesis serves to detoxify any residual a mmonia in perivenous cells. Experiments in vivo suggest that changes in net hepatic glutamine balance are due predominantly to regulation of glutamina se activity, with the flux through glutamine synthetase being relatively co nstant.