Intermediary metabolism of Arctic char Salvelinus alpinus during short-term salinity exposure

Abstract

SUMMARY The migration of Arctic char Salvelinus alpinus from freshwater to seawater requires a substantial reorganization of the osmoregulatory tissues to regulate plasma ion levels. These modifications have an inherent metabolic cost, which must be met through the upregulation of intermediary metabolism. Arctic char intermediary metabolism was monitored during the initial 96 h of seawater acclimation through measurement of key enzymes in gill, liver, red and white muscle as well as tissue and blood free amino acid (FAA) levels, and plasma glucose and non-esterified fatty acid content. In general, seawater exposure stimulated large changes in amino acid metabolism, but no change in lipid or carbohydrate metabolism. White muscle FAA content increased significantly following seawater exposure, with levels of essential FAAs doubling after 96 h. Similar increases were seen in the plasma, suggesting a rapid mobilization of FAAs to the circulation. These changes were accompanied by significant increases in the activities of enzymes involved in amino acid metabolism in the gill, liver, red and white muscle, suggesting seawater-acclimated fish have an enhanced capacity for energy production from amino acids. Increased energy requirements were evident in the gill of seawater-acclimated char, as citrate synthase activity increased significantly. The results of this study suggest a rapid upregulation of amino acid metabolism may be critical for the successful acclimation of Arctic char to seawater.

Changes in plasma osmolality, cortisol and amino acid levels of tongue sole (Cynoglossus semilaevis) at different salinities

“…As regard to other plasma amino acids, methionine, a compound with a critical role in cellular peroxidative protection (Obled et al, 2002), is the precursor of cysteine and glutathiomine. Histidine might be an important energy source in Arctic char gill as it can be converted to glutamate (Bystriansky et al, 2007). However, no significant changes of methionine and histidine were detected in the present study, which might owe to the species-specific differences of osmotic acclimation pattern in flatfish.…”

“…Changes in the plasma levels of free amino acid may be attributed to the amino acid requirements of fish (Wilson, 2002;Robinson et al, 2011). To date, only a few reports have discussed and integrated the changes of amino acid in seawater acclimation (Bystriansky et al, 2007).…”

Role for leptin in promoting glucose mobilization during acute hyperosmotic stress in teleost fishes

“…Hepatic gluconeogenesis has been examined only recently during early SW adaptation, despite historical reports of elevated nitrogen excretion rates (Evans et al 2005, Bystriansky et al 2007, Aragão et al 2010. This is probably due to two factors: i) free amino acids were thought to act as solutes to counter osmotic forces (Tseng & Hwang 2008) and ii) decreases in glycogen pointed to glycogenolysis as the source of glucose (Bashamohideen & Parvatheswararao 1972.…”

“…The accumulation of acetyl-CoA (fatty acid precursor), through the catabolism of ketogenic amino acids, may explain this effect (Jürss & Bastrop 1995; Fig. 4), as increases in plasma levels of the ketogenic amino acids leucine and isoleucine have been reported in SW-challenged Arctic char (Salvelinus alpinus; Bystriansky et al 2007). Thus, in addition to exerting an osmotic effect, SW-induced aminoacidemia may provide a mechanism for de novo synthesis of both carbohydrates and lipids.…”

“…Similarly, cortisol promotes hyperglycemia through gluconeogenesis in fishes and mammals (Vijayan et al 1996, Khani & Tayek 2001, but it also promotes sodium excretion through the gill during SW adaptation (Evans et al 2005). This steroid is lipolytic in vertebrates (Mommsen et al 1999), yet no changes in plasma free fatty acid levels or lipid oxidation rates reportedly occur in salinity-challenged salmonids (Bystriansky et al 2007).…”