Chapter 4 Tissue carbohydrate metabolism, gluconeogenesis and hormonal and environmental influences

Moon, Thomas W.; Foster, Glen D.

doi:10.1016/s1873-0140(06)80007-x

Cited by 96 publications

(78 citation statements)

References 146 publications

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“…Nevertheless, in fish fed the LFD, G6Pase was also strongly stimulated from day7 to day14, possibly because of the dietary protein level in the LFD (49%) relative to the HFD (26%) (Kirchner et al, 2003;Moon and Foster, 1995). Despite its higher G6Pase activity, our data show that the high protein level in the LFD did not negatively affect glycaemic control, and that G6Pase was even down-regulated in this group of fish.…”

Section: Metabolic Events Linked To the Hfd-induced Hyperglycaemiamentioning

confidence: 54%

High levels of dietary fat impair glucose homeostasis in rainbow trout

Figueiredo-Silva

Panserat

Kaushik

et al. 2012

Journal of Experimental Biology

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SUMMARYThis study was designed to assess the effects of dietary fat levels on glucose homeostasis in rainbow trout under prolonged hyperglycaemia induced by high carbohydrate intake. Trout were fed identical amounts of one of two iso-energetic diets containing either a low (LFD, 3%) or a high fat level (HFD, 20%) and similar amounts of digestible carbohydrates (26-30%) for 14days. While a single high fat meal reduced glycaemia compared with a low fat meal, the consumption of a high fat diet for 14days resulted in prolonged hypergylcaemia and reduced plasma glucose clearance in response to an exogenous glucose or insulin challenge. The hyperglycaemic phenotype in trout was characterised by a reduction of the activities of lipogenic and glucose phosphorylating enzymes with a concomitant stimulation of enzymes involved in glucose production in the liver and reduced glycogen levels in the white muscle. Impaired glucose tolerance (IGT) was further associated with a significant reduction of insulin receptor substrate 1 (IRS1) protein content in muscle, and with a poor response of HFD fed fish to an exogenous insulin load, suggestive of impaired insulin signalling in trout fed with a HFD. To our knowledge, this is the first study showing that a teleost can also develop a high fat-induced IGT, characterised by persistent hyperglycaemia and reduced insulin sensitivity, established symptoms of IGT and the prediabetic insulin-resistant state in mammals. Our results also provide evidence that persistent hyperglycaemia after a high carbohydrate meal stems from a metabolic interaction between dietary macronutrients rather than from high carbohydrate intake alone.

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Section: Metabolic Events Linked To the Hfd-induced Hyperglycaemiamentioning

confidence: 54%

High levels of dietary fat impair glucose homeostasis in rainbow trout

Figueiredo-Silva

Panserat

Kaushik

et al. 2012

Journal of Experimental Biology

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“…Whole blood glucose concentrations were measured as an index of physiological stress (Moon and Foster, 1995) using a OneTouch Ultra 2 blood glucose monitoring system (LifeScan, Milpitas CA, USA) (Clarkson et al, 2005) with ~5l of blood. Haematocrit was measured in duplicate using microcapillary tubes centrifuged at 6000g for 5min in an Autocrit Ultra 3 centrifuge (BD, Mississauga, ON, Canada).…”

Section: Analytical Techniquesmentioning

confidence: 99%

Chronic social stress impairs thermal tolerance in the rainbow trout (Oncorhynchus mykiss)

LeBlanc

Middleton

Gilmour

et al. 2011

Journal of Experimental Biology

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SUMMARYWhen faced with limited resources, juvenile salmonid fish form dominance hierarchies that result in social stress for socially subordinate individuals. Social stress, in turn, can have consequences for the ability of the fish to respond to additional stressors such as pathogens or exposure to pollutants. In the present study, the possibility that social stress affects the ability of rainbow trout (Oncorhynchus mykiss) to tolerate acute increases in water temperature was investigated. To this end, we first evaluated physiological and cellular stress responses following a 1h heat shock in juvenile fish in dominance hierarchies. We measured stress hormone (cortisol and catecholamines) concentrations and blood, brain and liver tissue levels of three heat shock proteins (HSPs), the stress inducible HSP70, the constitutive HSC70 and HSP90, in dominant and subordinate trout. No effects of social status on the hormonal response to the heat stress were detected, but the cellular heat shock response in the brain and liver of dominant and subordinate individuals was inhibited. We then assessed thermal tolerance in dominant and subordinate fish through critical thermal maximum temperature (CT max ) trials and measured HSPs following the heat shock. Subordinate fish were less thermally tolerant than their dominant counterparts. We conclude that social stress impacts the ability of fish to respond, on a cellular scale and in a tissue-specific manner, to increases in water temperature, with likely consequences for overall fitness.

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“…Although the role of cortisol in regulating energy-demanding pathways is not clearly known, studies have shown an enhancement of liver gluconeogenic capacity leading to elevated glucose production in fish (4,31,50). Indeed, this metabolic response is a key aspect of the stress recovery process, as glucose is the preferred fuel, especially for tissues such as gills and brain, to meet the increased energy demand (33). This glucose response with cortisol stimulation corresponded to an upregulation of PEPCK transcript levels, supporting enhanced gluconeogenic capacity (31).…”

Section: Metabolic Adjustmentsmentioning

confidence: 99%

Hepatic transcriptome response to glucocorticoid receptor activation in rainbow trout

Aluru

Vijayan

2007

Physiological Genomics

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Cortisol, the principal corticosteroid in teleosts, is thought to play a key role in the metabolic adjustments critical for regaining homeostasis. However, the target tissue molecular mechanisms involved in this adaptive response to corticosteroid stimulation are still unclear. Cortisol signaling is mediated predominantly by the glucocorticoid receptor (GR), and previous studies have shown that RU486 (a GR antagonist) offsets corticosteroid signaling in teleosts. To elucidate the molecular basis of GR-mediated metabolic readjustments, we exposed primary culture of trout hepatocytes in vitro to cortisol (to mimic stressed levels seen in fish), RU486, or a combination of both for 24 h. The gene expression was analyzed using a low-density custom-made rainbow trout cDNA array enriched with endocrine-, metabolic-, and stress-related genes. The microarray results for select genes were further validated using quantitative real-time PCR. Cortisol treatment significantly increased glucose production in hepatocytes, and this response was blocked by RU486, confirming GR-mediated corticosteroid signaling. Cortisol also elevated GR transcript levels, and this response was abolished by RU486, whereas both cortisol and RU486, either alone or in combination, reduced GR protein content in trout hepatocytes. Cortisol treatment significantly modulated the expression of several genes known to be involved in intermediary metabolism, cellular stress response, reproduction, and xenobiotic metabolism. Most of these cortisol-mediated transcript changes were abolished in the presence of RU486, suggesting a key role for GR-specific signaling in this adaptive response. Taken together, our results suggest a key role for genomic cortisol signaling in the liver molecular reprogramming that is critical for coping with stress in fish.RU486; cortisol; fish; Oncorhynchus mykiss; salmonid; cDNA microarray; stress response; intermediary metabolism CORTISOL, THE PRINCIPAL GLUCOCORTICOID in teleosts, is secreted by the interrenal tissues (analogous to the adrenal cortex) dispersed in the head kidney region. This steroid is involved in a diverse array of functions, including growth and metabolism, osmoregulation, immune function, and reproduction (31, 63). A well-studied role for cortisol involves tissue-specific metabolic reprogramming to cope with the increased energy demands associated with stress, but the associated molecular responses are far from clear. It is well established that cortisol actions are mediated via the glucocorticoid receptor (GR) belonging to the nuclear receptor family of ligand-bound transcription factors (46, 59).From a comparative standpoint, unlike mammals, teleosts appear to have multiple isoforms of GR (7,18,46), although the physiological role for each isoform is unknown. Also, some of the cortisol effects may be mediated via mineralocorticoid receptor (MR) activation; recently, an MR-specific ligand was identified in trout (46,56). In addition to genomic signaling mediated by GR and MR, recent studies also point to a no...

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Chapter 4 Tissue carbohydrate metabolism, gluconeogenesis and hormonal and environmental influences

Cited by 96 publications

References 146 publications

High levels of dietary fat impair glucose homeostasis in rainbow trout

High levels of dietary fat impair glucose homeostasis in rainbow trout

Chronic social stress impairs thermal tolerance in the rainbow trout (Oncorhynchus mykiss)

Hepatic transcriptome response to glucocorticoid receptor activation in rainbow trout

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