Effects of cortisol on hepatic carbohydrate metabolism and responsiveness to hormones in the sea raven, Hemitripterus americanus

Abstract

The sea raven, Hemitripterus americanus, is a sit-and-wait, low metabolic rate, marine teleost. The objective of this study was to determine i) whether cortisol implantation (50 mg. kg(-1)) for 7 days altered hepatocyte metabolism, and hepatocyte responsiveness to epinephrine, glucagon and insulin, and ii) whether 8 weeks of food-deprivation modified the above response. Cortisol implantation significantly increased hepatocyte total glucose production and oxidation from alanine compared to the sham group. There was no cortisol effect on glycogen breakdown, suggesting that the activation of other pathways, including gluconeogenesis, are required to account for the increased glucose production. Epinephrine-mediated (10(-)5M) glycogen breakdown and insulin-mediated (10(-8)M) total glucose production were enhanced in hepatocytes of cortisol implanted sea ravens, but there were no change in any glucagon (10(-7)M) effects. The enhanced glycogen breakdown in the absence of similar increases in total glucose production with epinephrine indicates mobilization of carbohydrate reserves for endogenous use by the liver.Food-deprivation for 8 weeks significantly decreased condition factor, plasma cortisol concentration and liver glycogen content in the sea raven, but had no effect on plasma glucose concentration. Hepatocyte total glucose production and flux rates from alanine increased significantly with food-deprivation. Moreover, food-deprivation increased responsiveness of total hepatocyte glucose production to the actions of glucagon and insulin, but not to epinephrine; none of these effects were modified by cortisol implantation.Our results indicate that cortisol in the sea raven exerts both a direct and an indirect or permissive effect on hepatocyte metabolism by modifying hepatocyte responsiveness to epinephrine and insulin stimulation. Cortisol implantation did not modify the effects of glucagon or food-deprivation in this species.

Divergence of endocrine and metabolic responses to stress in two rainbow trout lines selected for differing cortisol responsiveness to stress

“…Of course, hormones other than the catecholamines and cortisol, such as thyroxine and glucagon, are implicated in glycogen breakdown (Janssens and Waterman, 1988;Soengas et al, 1992b). Enhanced glycogen breakdown in the absence of increased total glucose production has previously been interpreted to indicate a mobilization of carbohydrate reserves for endogenous use by the liver (Vijayan et al, 1993). …”

Influence of food deprivation and high stocking density on energetic metabolism and stress response in red porgy, Pagrus pagrus L

“…High stocking density is a common chronic stressor in aquaculture that activates stress response (Barton and Iwama 1991), affecting different metabolic pathways related to lipid (Montero et al 1999), carbohydrate (Vijayan et al 1993;SangiaoAlvarellos et al 2005), and protein Costas et al 2008) metabolisms. Food deprivation is another common type of stress that fish experience in aquaculture practices.…”

Experimental control of stress hormone levels in fishes: techniques and applications

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