Fasting modulates metabolic responses to cortisol, GH and IGF‐I in Arctic charr hepatocytes

Abstract

Hepatocytes in primary culture from fed and 2 month fasted Arctic charr Salvelinus alpinus were exposed to physiological doses of either cortisol, salmon growth hormone (GH), salmon insulin-like growth factor-I (IGF-I) or a combination of salmon GH and salmon IGF-I. Fasting significantly lowered medium glucose levels compared to the fed fish, but had no significant effects on hepatocyte glycogen content or on the activities of enzymes involved in the intermediary metabolism. Cortisol treatment had no effect on hepatocyte glycogen content or on the enzyme activities investigated, but resulted in a significant increase in medium glucose concentration in hepatocytes isolated from fasted, but not fed fish. GH and IGF-I treatments, both singly and in combination, significantly increased the glycogen content of hepatocytes isolated from fed fish, with less pronounced effects on hepatocytes isolated from fasted fish. The combination of GH and IGF-I significantly increased lactate dehydrogenase activity regardless of the feeding state and significantly reduced the phosphenolpyruvate carboxykinase activity and medium glucose concentration in hepatocytes isolated from fed fish. Further, GH and IGF-I significantly increased the activities of alanine aminotransferase and aspartate aminotransferase in hepatocytes isolated from fasted fish, but not fed fish. There were no effects of GH, IGF-I, or their combination, on glucose 6-phosphate dehydrogenase or 3-hydroxyacylCoA dehydrogenase activities. The results demonstrated that nutritional status of the animal modulates hepatocyte responsiveness to metabolic hormones, and suggested a role for GH and IGF-I in hepatic glycogen conservation. # 2005 The Fisheries Society of the British Isles

Recombinant Bovine Growth Hormone-Induced Metabolic Remodelling Enhances Growth of Gilthead Sea-Bream (Sparus aurata): Insights from Stable Isotopes Composition and Proteomics

“…Our results clearly indicated a reduction in muscle protein fractionation in juveniles of gilthead sea bream due to the injection of rBGH, which is interpreted as a positive balance on protein growth that in turn can be associated with higher synthesis or with reduced degradation. In this sense, the reduction of hepatic ALAT in the group injected with rBGH would be another evidence of the reduction in protein recycling in this group, in agreement with that observed in other teleost injected with GH [ 27 ] or in in vitro treated hepatocytes [ 22 ]. The observed decrease in nitrogen fractionation, as a result of decreased δ 15 N, a reliable indicator of nutritional status in fish [ 37 ], implies a reduction in protein turnover and a protein sparing as we observed previously in the same species submitted to changes in diet or swimming activity [ 35 , 36 , 37 , 49 ].…”

“…The significant enrichment of the δ 13 C from the glycogen reserve, and the increase in concentration of this metabolite in both muscles would indicate a turnover modification of this reserve with a positive balance for the synthesis and/or decrease of its degradation as a consequence of rBGH injection. In this way, GH and IGF-I treatments, both singly or in combination, significantly increased the glycogen content of hepatocytes isolated from Arctic char [ 27 ], in agreement with that observed in mammals [ 18 ]. Thus, the present results showed that there is a shift in the preferential use of energy substrates in response to GH treatment also in gilthead sea bream, with a greater use of lipids and a reduction in carbohydrate utilization, as observed in mammals.…”

“…As in mammals [ 18 ], GH has a dual role in fish, since it exerts a lipolytic effect on target tissues such as liver and adipose tissue in vivo [ 12 , 19 , 20 ] and in vitro [ 12 , 21 , 22 ], and at the same time, it has a hyperglycaemic effect by mobilizing liver glycogen [ 23 , 24 , 25 , 26 ]. GH and IGF-I treatments, both singly and in combination, significantly increased the glycogen content of hepatocytes isolated from fed Artic char [ 27 ]. Thereby, in vivo GH administration suppressed the potential for glycolysis but stimulated gluconeogenic and glycogenolytic pathways.…”