Mechanisms of increased gluconeogenesis from alanine in rat isolated hepatocytes after endurance training.

This work aimed at further investigating the mechanisms by which liver gluconeogenic capacity from alanine is improved after training in rats, with an isolated hepatocyte model. Compared with controls in hepatocytes from trained rats incubated with gluconeogenic precursors (20 mM), the glucogenic flux (J(glucose)) was increased by 64% from alanine (vs. 21% for glycerol, 18% for lactate-pyruvate 10:1, and 10% for dihydroxyacetone). Maximal intracellular alanine accumulation capacity was also increased by 50%. Further experiments conducted on perifused hepatocytes showed that the putative adaptation at the level of the phosphoenolpyruvate-pyruvate cycle, which could be involved in the increased J(glucose) from lactate-pyruvate, was not involved in the increased J(glucose) from alanine after training. For alanine concentration higher than approximately 1 mM, an increased flux through alanine aminotransferase appeared responsible for the increased J(glucose). This could, in turn, depend on an increased supply of cytosolic 2-oxoglutarate because of the higher mitochondrial respiration observed in hepatocytes from trained rats and the activation of the malate-aspartate shuttle. At lower alanine concentration, the increase in J(glucose) appeared to be entirely due to the improved transport capacity.