Differential effects of long-term leucine infusion on tissue protein synthesis in neonatal pigs

In neonatal pigs, a continuous intravenous infusion of leucine at 400 μmol/kg/h increases activation markers of the mTOR pathway in muscle, liver, and pancreas, but only increases protein synthesis in these tissues when amino acids are simultaneously infused to maintain normal blood levels.

In newborn pigs, giving extra leucine without other amino acids does not increase protein production in muscle, liver, or pancreas, even though a key signaling pathway called mTOR is activated, showing that mTOR activation alone cannot drive protein synthesis without sufficient building blocks from other amino acids.

In newborn pigs, giving leucine activates mTOR signaling in all types of skeletal muscle and increases protein synthesis only if amino acids are present at sufficient levels.

In newborn pigs, continuous leucine infusion does not increase protein synthesis in the heart, kidney, or jejunum, even though mTOR signaling is activated in some tissues, showing that leucine’s effect on protein synthesis varies by organ.

In newborn pigs, giving leucine increases the amount of protein made per ribosome in muscle and liver tissues only when amino acids are available at normal levels.

When leucine remains in the bloodstream for extended periods, skeletal muscle shows a diminished capacity to initiate protein synthesis in response to that leucine.