The Influence of Social Status on Hepatic Glucose Metabolism in Rainbow Trout Oncorhynchus mykiss

SUMMARY Rainbow trout (Oncorhynchus mykiss) are known to use dietary carbohydrates poorly. One of the hypotheses to explain the poor utilisation of dietary glucose by these fish is a dysfunction in nutritional regulation of hepatic glucose metabolism. In this study, we obtained partial clones of rainbow trout cDNAs coding for a glucose transporter (Glut2), and for the enzymes 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (6PF-2K/F-2,6BPase), fructose-1,6-bisphosphatase (FBPase) and pyruvate kinase (PK). Their deduced amino acid sequences were highly similar to those of mammals (up to 80% similarity). In a study of nutritional regulation, the Glut2 gene was highly expressed in the liver irrespective of the nutritional status of the trout, in agreement with the role of this transporter in the input (during refeeding) and output (during fasting) of glucose from the liver. Moreover, whereas PK and FBPase gene expression was high irrespective of the nutritional status, levels of hepatic 6PF-2K/F-2,6BPase mRNA were higher in fish fed with carbohydrates than in fish deprived of food. The high levels of hepatic PK, Glut2 and 6PF-2K/F-2,6BPase gene expression observed in this study suggest a high potential for tissue carbohydrate utilisation in rainbow trout. The persistence of a high level of FBPase gene expression suggests an absence of regulation of the gluconeogenic pathway by dietary carbohydrates.

Download Full-text

Diminished social status affects ionoregulation at the gills and kidney in rainbow trout (Oncorhynchus mykiss)

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f04-032 ◽

2004 ◽

Vol 61 (4) ◽

pp. 618-626 ◽

Cited By ~ 22

Author(s):

Katherine A Sloman ◽

Graham R Scott ◽

D Gordon McDonald ◽

Chris M Wood

Keyword(s):

Rainbow Trout ◽

Oncorhynchus Mykiss ◽

Social Status ◽

Metabolic Cost ◽

Whole Body ◽

Sodium Reabsorption ◽

Plasma Sodium ◽

Sodium Efflux ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Uptake Rates

Competition for social status can result in physiological differences between individuals, including differences in ionoregulatory ability. Subordinate rainbow trout (Oncorhynchus mykiss) had two-fold higher uptake rates of sodium across the gill and two-fold higher whole-body sodium efflux rates than the dominant fish with which they were paired. Sodium efflux was then divided into branchial and renal components, both of which were higher in subordinates. Branchial sodium efflux accounted for 95%98% of sodium loss. Plasma sodium concentrations were more variable, although not significantly different, in subordinate fish, suggesting that the increased loss of sodium in these trout is compensated for by an increase in uptake rates. Urine flow rates and plasma cortisol concentrations were higher in subordinate fish, but there was no difference in glomerular filtration rate between dominants and subordinates. Renal sodium reabsorption was significantly reduced in subordinates. In summary, the ionoregulation of subordinate individuals was altered, most likely occurring as a result of stress-induced changes in gill permeability, resulting in a higher throughput of water and increased branchial sodium efflux. These changes in ionoregulatory ability have many physiological implications, including the increased susceptibility of subordinates to ionoregulatory challenges and an increased metabolic cost of ionoregulation.

Download Full-text

Sex differences in cardiac glucose metabolism and function in immature rainbow trout ( Oncorhynchus mykiss )

The FASEB Journal ◽

10.1096/fasebj.21.6.a867-b ◽

2007 ◽

Vol 21 (6) ◽

Author(s):

Pavan K Battiprolu ◽

Adam C Goddard ◽

Ken J Rodnick

Keyword(s):

Sex Differences ◽

Rainbow Trout ◽

Glucose Metabolism ◽

Oncorhynchus Mykiss ◽

Rainbow Trout Oncorhynchus Mykiss ◽

And Function

Download Full-text

Endocrine control of oleic acid and glucose metabolism in rainbow trout (Oncorhynchus mykiss) muscle cells in culture

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00696.2009 ◽

2010 ◽

Vol 299 (2) ◽

pp. R562-R572 ◽

Cited By ~ 24

Author(s):

Joan Sánchez-Gurmaches ◽

Lourdes Cruz-Garcia ◽

Joaquím Gutiérrez ◽

Isabel Navarro

Keyword(s):

Oleic Acid ◽

Rainbow Trout ◽

Glucose Metabolism ◽

Oncorhynchus Mykiss ◽

Acid Metabolism ◽

Peroxisome Proliferator ◽

Endocrine Control ◽

Peroxisome Proliferator Activated Receptor ◽

Rainbow Trout Oncorhynchus Mykiss ◽

Igf I

The effects of insulin and IGF-I on fatty acid (FA) and glucose metabolism were examined using oleic acid or glucose as tracers in differentiated rainbow trout ( Oncorhynchus mykiss ) myotubes. Insulin and IGF-I significantly reduced the production of CO2 from oleic acid with respect to the control values. IGF-I also significantly reduced the production of acid-soluble products (ASP) and the concentration of FA in the medium, while cellular triacylglycerols (TAG) tended to increase. Only insulin produced a significant accumulation of glycogen inside the cells in glucose distribution experiments. Incubation with catecholamines did not affect oleic acid metabolism. Cells treated with rapamycin [a target of rapamycin (TOR) inhibitor] significantly increased the oxidation of oleic acid to CO2 and ASP, while the accumulation of TAG diminished. Rosiglitazone (a peroxisome proliferator-activated receptor γ agonist) and etomoxir (a CPT-1 inhibitor) produced a severe and significant reduction in the production of CO2 and ASP. Rosiglitazone and etomoxir also produced a significant accumulation of FA outside and inside the cells, respectively. No significant effects of these drugs on glucose distribution were observed. These data indicate that insulin and IGF-I act as anabolic hormones in trout myotubes in both oleic acid and glucose metabolism, although glucose oxidation appears to be less sensitive than FA oxidation to insulin and IGF-I. The use of rapamycin, etomoxir, and rosiglitazone may help us to understand the mechanisms of regulation of lipid metabolism in fish.

Download Full-text