Metabolic organization of the sturgeon Acipenser naccarii: A comparative study with rainbow trout Oncorhynchus mykiss

In order to assess the metabolic organization of Acipenser naccarii, a representative species of the ancient ancipenserid chondrosteans, the activity of key enzymes of the main metabolic pathways in the liver, white muscle, and heart, as well as the levels of plasma and tissue metabolites of this sturgeon species have been evaluated and compared to those of the advanced teleost Oncorhynchus mykiss. In general, the epibenthic character of A. naccarii is reflected in the lower specific activity of most enzymes evaluated, in comparison to those of the more active O. mykiss. However, the metabolic organization of this sturgeon species shows some particularities that clearly differed from that of teleosts. Whereas the liver is the main gluconeogenic organ in rainbow trout, both the liver and white muscle of sturgeon possess the same capacity for glucose synthesis, with glycerol being the more suitable glucose precursor. Unlike teleosts, the liver is the main site for lipid storage in sturgeon which would be related to its lower capacity to transport metabolites involved in lipid metabolism. Although the capacity to transport free fatty acids (FFA) is lower in sturgeon than in trout, HOAD activity shows that this acipenserid is able to oxidize fatty acids in extrahepatic tissues such as the heart. Also, both sturgeon and trout showed the same hepatic capacity to oxidize fatty acids. The liver of sturgeon possesses a higher capacity to synthesize ketone bodies than trout which would be a primitive trait to export these compounds as fuels for peripheral tissues in order to offset the low ability to transport FFA in the blood.