The regulation of liver protein degradation by aminoacids in vivo. Effects of glutamine and leucine.

The effects in vivo of the two major in vitro regulatory aminoacids, leucine and glutamine, on liver protein degradation were explored in male young adult Sprague Dawley rats. Protein degradation was stimulated by the injection of the antilipolytic drug 3,5 dimethylpyrazole (DMP), which rises glucagon and lowers insulin plasma levels. At the appropriate time-points (20 and 40 min) after the injection of DMP, glutamine or leucine (12.5 mg/kg b.w.) were injected intraperitoneally. The rate of liver protein breakdown was evaluated 60 min after the injection of DMP on the basis of the release of valine into the perfusate during a short term single pass liver perfusion. The aminoacid was assayed by an HPLC procedure. Results show that the administration of glutamine inhibited the DMP-induced increase in the rate of valine release from the perfused liver whereas the administration of leucine did not; neither of the aminoacids appeared to have any effect on the metabolic or endocrine changes that are required for the induction of liver autophagy and protein breakdown by DMP. It is concluded that the aminoacid glutamine has a powerful action on the in vivo regulation of liver protein breakdown, which is not apparent with leucine.