CULTURED TROUT LIVER-CELLS - UTILIZATION OF SUBSTRATES AND RESPONSE TO HORMONES

The characterization of a recently established system for the short-te rm culture of rainbow trout (Oncorhynchus mykiss) liver cells in chemi cally defined medium has been extended to studies on the metabolic com petence of the cells and the characterization of their response to hor mones. Three areas of metabolism have been addressed: a) the utilizati on of the exogenously added substrates fructose, lactate, glucose, dih ydroxyacetone, and glycerol for glucose and lactate formation; b) the effects of the pancreatic hormones insulin and glucagon on cellular gl ucose formation, lactate formation, and fatty acid synthesis; and c) t he effects of insulin and dexamethasone on the estradiol-dependent pro duction of vitellogenin. Incubation of trout liver cells with fructose , lactate, glucose, dihydroxyacetone, or glycerol resulted in enhanced rates of cellular glucose and lactate production. Substrate-induced e ffects usually were more clearly expressed after extended (20 h) than after acute (5 h) culture periods. Addition of the hormones insulin or glucagon caused dose-dependent alterations in the flux of substrates to glucose and lactate. Rates of de novo synthesis of fatty acids from [C-14]acetate were stimulated by insulin and inhibited by glucagon du ring acute and extended incubation periods. Treatment of liver cells i solated from male trout for 72 h with estradiol induced vitellogenin p roduction and secretion into the medium. However, the addition of insu lin or dexamethasone drastically reduced this estrogen-induced vitello genesis. These results indicate that trout liver cells cultured in def ined medium maintain central metabolic pathways, including glycolysis, gluconeogenesis, lipogenesis, and vitellogenesis as well as their res ponsiveness to various hormones, for at least 72 h. This cell culture system should provide an excellent model to further characterize metab olic processes in fish liver.