AAS-HANSEN, �.*; J�RGENSEN, E.H.; VIJAYAN, M.M.; Univ. of Waterloo, ON, Canada (Present institutions: Norwegian Institute for Nature Research and Univ. of Troms�, Troms�, Norway); Norwegian Institute for Nature Research, Troms�, Norway; Univ. of Waterloo, ON, Canada: Hormonal control of hepatocyte metabolism in Arctic charr
Anadromous Arctic charr, Salvelinus alpinus, perform seasonal migrations between fresh water and seawater. Prior to seaward migration, anadromous salmonids undergo a series of physiological, morphological and behavioral changes pre-adaptive for marine residency (smoltification). Hormones such as cortisol, growth hormone (GH) and insulin-like growth factor-I (IGF-I) are known to play a role in smoltification by stimulating the development of hyposmoregulatory capacity. Also, these hormones are thought to be important for growth and metabolism, although the mode of action is not clear. In this study, we investigated the metabolic role of cortisol, GH and IGF-I by examining their impact on liver metabolism in fed and fasted Arctic charr. To this end, primary cultures of hepatocytes isolated from either fed or fasted (2 months at 12° C) charr were stimulated with physiological doses of cortisol, GH, IGF-I or a combination of GH and IGF-I. Cortisol stimulated glucose release from these hepatocytes without altering glycogen content suggesting a role in gluconeogenesis. GH and IGF-I, either singly or in combination, did not affect glucose release, but resulted in higher hepatocyte glycogen content reflecting a glyconeogenic role for these hormones in charr hepatocytes. We also examined the effect of these hormones on several enzymes involved in the intermediary metabolism. Taken together, our results clearly allude to an important role for these hormones in the energy substrate re-partitioning process in Arctic charr.
