In vitro hepatocyte metabolism of alanine and glucose and the response to insulin in fed and fasted rainbow trout

Abstract

Rainbow trout (Oncorhynchus mykiss) fasted for 4 months had lower plasma glucose concentration and hepatocyte glycogen content than the fed fish. Gluconeogenesis from alanine in the fasted fish was not significantly different from that of the fed fish, whereas both alanine glyconeogenesis and oxidation increased with fasting by 400% and 300%' respectively. Glyconeogenesis from glucose was not significantly different with fasting, whereas glucose oxidation decreased significantly with fasting. The presence of glucose (10 mM) in the medium did not modify alanine glyconeogenesis or gluconeogenesis in either the fed or the fasted groups. However, glucose did increase alanine oxidation in the fed group but not in the fasted group, this response being further stimulated in the presence of insulin. Alanine (2 mM) in the medium had no effect on glyconeogenesis from glucose in either fed or fasted trout hepatocytes. Insulin significantly decreased glucose oxidation in the fed fish, whereas the insulin effect on glucose oxidation in the fasted fish occurred only in the presence of alanine. The results indicate that nutritional state affects hepatocyte responsiveness to substrate utilization and insulin stimulation in trout. Specifically, the hepatocyte potential for glyconeogenesis is enhanced in the fasted fish, although this increased glycogen production is not due to an increased glucose utilization. o 1995 Wiley-Liss, Inc.

Food deprivation and refeeding in Atlantic salmon,Salmo salar: effects on brain and liver carbohydrate and ketone bodies metabolism

“…However, a decrease was observed in brain LDH activity of food deprived fish in Experiment 1 and we do not know how to explain these somewhat contradictory results. Plasrna glucose concentrations are usually maintained in starved fish either by reducing the rate of glucose use and/or by increasing gluconeogenesis (Pereira et al 1995). Liver glycogenolytic potential was apparently increased in food deprived Atlantic salmon, which is in accordance with the general trend observed in salmonid species (Navarro et a/.…”

“…No further mobilization was observed fiom day 7 to day 42 of food deprivation suggesting a partial protection of glycogen stores, in a way similar to that previously reported in sahnonids (Vijayan and Moon 1992;Vijayan et al 1993) and also in other species (Hemre et al 1993). In Dct, the replenishment of glycogen reserves may have become a priority over that of fiee glucose production, resulting in lower plasma glucose concentration in food deprived fish as suggested by Pereira et al (1995). Changes observed in GPase and GSase activities in livers of food deprived fish agree with those of glycogen levels, especially when the GSase a/GPase a activity ratio is considered.…”

Nutritional and hormonal control of lipolysis in isolated gilthead seabream (Sparus aurata) adipocytes

“…The relative increase in lipolysis after GH incubations in fasted fish was lower than in fed fish, which could be a consequence of the already higher rate of lipolysis in fasted fish. From our data, we cannot deduce a change in hormone sensitivity, although in other fish models, such as hepatocytes, fasting affected the responsiveness to hormone stimulation (13,26).…”

High dietary protein combats the stress of Labeo rohita fingerlings exposed to heat shock

“…Since glycogen is an important energy reserve that can be rapidly mobilized during stress, heat shock L. rohita fed with 40 and 45% CP restored the liver glycogen content at the expense of protein. Pereira et al (1995) reported that chronically stressed O. mykiss maintains liver glycogen content at the expense of other substrates, particularly alanine.…”