In vivo effects of the steroid analogue RU486 on some aspects of intermediary and thyroid metabolism of brook charr, Salvelinus fontinalis

Evaluation of the effects of exogenous cortisol manipulation and the glucocorticoid antagonist, RU486, on the exploratory tendency of bluegill sunfish (Lepomis macrochirus)

In teleost fishes, activation of the hypothalamic-pituitary-interrenal axis leads to an elevation of circulating cortisol levels as a primary stress response. While acute elevation of cortisol is generally beneficial, long-term elevation, a common characteristic of chronic stress, may lead to detrimental effects on health and physiological performance in fishes. Some stress-mediated behavioural shifts, such as variation along the shy-boldness axis in fish, may influence individual fitness. The present study evaluated the role of cortisol and its mechanisms of action in the exploratory behaviour of the bluegill sunfish (Lepomis macrochirus). Fish were implanted with cocoa butter alone (sham treatment), or cocoa butter containing cortisol, or cortisol and the glucocorticoid receptor antagonist, RU486. A control (untreated) group was also used. Animals were held for 48 h following treatment and then were subjected to a Z-maze trial to characterize the exploratory behaviour. Cortisol treatment had no measurable effect on the exploratory behaviour of bluegill sunfish. Despite presenting a higher probability of refuge emergence, fish treated with cortisol combined with RU486 behaved similarly to cortisol-treated and control groups. While these results suggest that cortisol may not be involved in the mechanisms controlling boldness, the influence of cortisol elevation across longer time periods plus validation in different contexts will be necessary to confirm this conclusion.

Combined antagonist treatment of glucocorticoid and mineralocorticoid receptor does not affect weight loss of fasting rainbow trout but inhibits a fasting-induced elevation of cortisol secretion

The gastrointestinal system of fish reacts rapidly to food deprivation. The relative masses of digestive organs and activities of digestive enzymes decrease within days of fasting. This is believed to be an energy-conserving strategy as the metabolic cost of maintaining digestive capacity is high. Cortisol is known for its role in energy mobilization following stress exposure, and prolonged elevated cortisol levels have been shown to reduce growth rates in fish. Fish experiencing chronic cortisol elevations show structural changes to their digestive tissues and overall reductions in relative digestive tissue masses. In fish fasting for prolonged periods, circulating cortisol levels have been reported to be downregulated, upregulated, or unchanged compared to feeding fish. This study aimed to investigate if RU486 and spironolactone, antagonists of the glucocorticoid receptor (GR), and mineralocorticoid receptor (MR), respectively, alone or in combination affect circulating cortisol levels during prolonged starvation. In addition, we tested the effects of blocking GR and MR, on the down-regulation of relative digestive tissue mass during starvation, and its effects on weight loss. Three treatment groups of rainbow trout were intraperitoneally implanted with either GR, MR, or GR and MR blockers. A fourth group was implanted with cortisol, while a fifth group served as a control. All treatment groups were sampled over a course of four weeks of food deprivation and compared against each other and fed control fish at day 0 of the trial. Starvation for 2 weeks and longer significantly increased circulating cortisol levels in all groups except for the group implanted with GR and MR antagonists. Loss of body mass occurred most rapidly during the first week of starvation. Spironolactone treatment resulted in significantly reduced loss of mass during the first week, however, over the following weeks, no differences in mass loss were observed in the groups implanted with blockers, while cortisol-treated fish showed the highest decrease in body mass over time. Relative digestive tissue mass decreased in all groups but apparently, the fasting-induced elevation in plasma cortisol levels did not affect the relative weight loss of digestive tissues as no differences were observed between control fish and GR + MR antagonist treated fish. Very high cortisol levels caused by cortisol treatment however caused a faster decrease in the relative mass of some digestive organs, particularly the stomach.

Treatment with the glucocorticoid antagonist RU486 reduces cooperative cleaning visits of a common reef fish, the lined bristletooth

Cooperation often involves a conflict of interest. This is particularly true in situations where one individual seeks out a service but cannot properly control the quality of the service given by the partner who would gain from defecting. An example is cleaning mutualism involving the bluestreak cleaner wrasse (Labroides dimidiatus) and its reef-fish 'clients'. These cleaners may reduce the stress experienced by their clients by removing parasites; however they occasionally cheat clients (i.e. defect) by eating mucus and other living tissues. Here we present experimental support for the hypothesis that stress responses increase the motivation for clients to seek out such risky asymmetric interactions. We manipulated the stress response by blocking glucocorticoid receptors with the antagonist RU486 in a species that is a regular visitor of cleaner fish, the lined bristletooth (Ctenochaetus striatus). Field observations 1 week after treatment with RU486 showed that antagonist treatment led to a reduction in cleaning duration compared to control treatment. This was not explained by a general effect on client behavior as intraspecific social behavior appeared unaffected. We propose that antagonist treatment reduced stress responses to the presence of ectoparasites, which in turn reduced the client's perception of benefits from seeking out cleaning interactions. The results demonstrate a hitherto overlooked variable role of stress and stress responses on cooperative behavior.

The role of thyroid hormones in stress response of fish

Thyroxine (T(4)) and triiodothyronine (T(3)), the principal thyroid hormones (THs) secreted from the hypothalamic-pituitary-thyroid (HPT) axis, produce a plethora of physiologic actions in fish. The diverse actions of THs in fishes are primarily due to the sensitivity of thyroid axis to many physical, chemical and biological factors of both intrinsic and extrinsic origins. The regulation of THs homeostasis becomes more complex due to extrathyroidal deiodination pathways by which the delivery of biologically active T(3) to target cells has been controlled. As primary stress hormones and the end products of hypothalamic-pituitary-interrenal (HPI) and brain-sympathetic-chromaffin (BSC) axes, cortisol and adrenaline exert its actions on its target tissues where it promote and integrate osmotic and metabolic competence. Despite possessing specific osmoregulatory and metabolic actions at cellular and whole-body levels, THs may fine-tune these processes in accordance with the actions of hormones like cortisol and adrenaline. Evidences are presented that THs can modify the pattern and magnitude of stress response in fishes as it modifies either its own actions or the actions of stress hormones. In addition, multiple lines of evidence indicate that hypothalamic and pituitary hormones of thyroid and interrenal axes can interact with each other which in turn may regulate THs/cortisol-mediated actions. Even though it is hard to define these interactions, the magnitude of stress response in fish has been shown to be modified by the changes in the status of THs, pointing to its functional relationship with endocrine stress axes particularly with the interrenal axis. The fine-tuned mechanism that operates in fish during stressor-challenge drives the THs to play both fundamental and modulator roles in stress response by controlling osmoregulation and metabolic regulation. A major role of THs in stress response is thus evident in fish.

Systemic thyroid hormone is necessary and sufficient to induce ultraviolet-sensitive cone loss in the juvenile rainbow trout retina

Rainbow trout possess ultraviolet-sensitive (UVS) cones in their retina that degenerate naturally during development. This phenomenon can be induced with exogenous thyroxine [T4, a thyroid hormone (TH)] treatment. However, the previous T4 exposure experiments employed static water immersion; a method that could introduce confounding stress effects on the fish. Because of this, it was uncertain if T4 alone was sufficient to induce retinal changes or if stress-related hormones were also necessary to initiate this process. Furthermore, it was unclear whether endogenous T4 was the factor responsible for initiating natural UVS cone loss during development. The current study examined the role of systemic T4 on the juvenile rainbow trout retina using a slow-release implant. Exogenous T4 treatment resulted in SWS1 opsin downregulation and UVS cone loss after four weeks of exposure, signifying that T4 is sufficient to induce this process. Blocking endogenous T4 production with propylthiouracil (PTU, an anti-thyroid agent) attenuated SWS1 downregulation and UVS cone loss in the retina of naturally developing rainbow trout, suggesting that endogenous T4 is necessary to initiate retinal remodelling during development. Quantitative real-time RT-PCR analysis demonstrated that several TH-regulating components are expressed in the trout retina, and that expression levels of the TH receptor isoform TRbeta and the type 2 deiodinase (D2) change with T4 treatment. This suggests that T4 may act directly on the retina to induce UVS cone loss. Taken together, these results demonstrate that systemic TH is necessary and sufficient to induce SWS1 opsin downregulation and UVS cone loss in the retina of juvenile rainbow trout.

The regulatory role of glucocorticoid and mineralocorticoid receptors in pulsatile urea excretion of the gulf toadfish,Opsanus beta

Gulf toadfish, Opsanus beta, are one among a group of unusual teleosts that excrete urea as their predominant nitrogen end product in response to stressful conditions. Under conditions of crowding or confinement,fasted toadfish excrete the majority of their nitrogen waste in large pulses of urea (>90% of total nitrogen) lasting up to 3 h. An earlier study demonstrated that cortisol has an inhibitory influence on urea pulse size. The present study tested the hypothesis that cortisol mediates changes in urea pulse size in ureotelic toadfish through the glucocorticoid receptor (GR) and not the mineralocorticoid receptor (MR). In vivo pharmacological investigations were used to manipulate the corticosteroid system in crowded toadfish, including experimentally lowering plasma cortisol levels by the injection of metyrapone, blocking cortisol receptors through exposure to either RU-486 (GR antagonist) and spironolactone (MR antagonist), or through exogenous infusion of the tetrapod mineralocorticoid aldosterone (tetrapod MR agonist). The data demonstrate that lowering the activity of cortisol, either by inhibiting its synthesis or by blocking its receptor, resulted in a two- to threefold increase in pulse size with no accompanying change in pulse frequency. Treatment with spironolactone elicited a minor (∼1.5-fold)reduction in pulse size, as did aldosterone treatment, suggesting that the anti-mineralocorticoid spironolactone has an agonistic effect in a piscine system. In summary, the evidence suggests that urea transport mechanisms in pulsing toadfish are upregulated in response to low cortisol, mediated primarily by GRs, and to a lesser extent MRs.

Biochemical and stress responses of rohu Labeo rohita and mrigal Cirrhinus mrigala in relation to acclimation temperatures

The biochemical and stress responses of two Indian major carps, rohu Labeo rohita and mrigal Cirrhinus mrigala were studied after acclimating them to four preset temperatures (26, 31, 33 and 36 degrees C) for 30 days. The blood glucose and liver glycogen levels showed an inverse trend in both the species and were significantly different in L. rohita at higher temperatures. The decrease in the liver glycogen level of C. mrigala, however, was not significant. Plasma cortisol levels increased significantly whereas the ascorbic acid content in the brain and kidney of both the species decreased significantly with increasing temperatures. Total lipid content in the liver of both the species decreased significantly with increasing acclimation temperatures. The phospholipid concentration decreased in L. rohita with increasing acclimation temperatures, and in C. mrigala the values decreased up to 33 degrees C and increased at 36 degrees C. In C. mrigala, the cholesterol level decreased up to 33 degrees C and then increased at 36 degrees C, but the absolute value was lower in comparison to L. rohita. The cholesterol levels, however, were not significantly different in L. rohita. Triglycerides and free fatty acids concentrations decreased significantly with increasing acclimation temperatures in both the species. The present study indicates species-specific metabolic responses of L. rohita and C. mrigala to thermal acclimation.

Hepatic transcriptome response to glucocorticoid receptor activation in rainbow trout

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.

Cortisol is necessary for seawater tolerance in larvae of a marine teleost the summer flounder

Larval-stage summer flounder (Paralichthys dentatus) were immersed in the corticosteroid-receptor blocker RU486 to test the effects of cortisol deficiency on salinity tolerance. Premetamorphic larvae held at 10 (near isosmotic) or 30 (hyperosmotic) parts per thousand ( per thousand) seawater survived well over 5d in 0, 0.012, or 0.12 microM RU486. However, at concentrations of 1.2 or 3.6 microM RU486, mortality was significantly greater for larvae in 30 per thousand compared to larvae in 10 per thousand. In a separate experiment, the ability of RU486 to inhibit tolerance to hyperosmotic medium (30 per thousand) was confirmed; immersion at 1.2 microM RU486 induced mortality of larvae in the metamorphic climax stage held at 30 per thousand, but not 0 or 10 per thousand. Mortality due to RU486 in pre- or prometamorphic stage larvae was prevented by concurrent immersion in cortisol at concentrations approximately 10-200 times greater than RU486, indicating that the action of RU486 was specific to antagonism of cortisol. The efficacy of 1.2 microM RU486 in reducing survival in 30 per thousand was found to be stage-dependent and exhibited the following hierarchy for fastest time to 50% mortality: prometamorphosis>metamorphic climax>premetamorphosis. In a 5-d pretreatment of pre- or prometamorphic larvae by immersion in 20 microM cortisol and/or 0.12 microM RU486 at 30 per thousand, only RU486 had a limited effect on decreasing survival when larvae were challenged with abrupt exposure to 50 per thousand. In total, the results evidence for the first time a necessary role for cortisol in seawater tolerance of a larval marine teleost.

Quantification of a glucocorticoid receptor in sea bass (Dicentrarchus labrax, L.) reared at high stocking density

To assess the effects of environmental stress conditions on fish, the examination of a suite of biomarkers, including endocrine parameters, has been suggested. In teleosts, glucocorticoids, including cortisol and corticosterone, are known to mediate stress response. Inside the cell, they bind to a high-affinity cytosolic glucocorticoid receptor (GR), which acts as ligand-dependent transcription factor to control and regulate gene expression. Receptor number or affinity may directly influence the degree of reactivity of target cells. GR transcripts have been cloned and characterized in different fish species, but no studies, to date, are available on the quantification of GR in sea bass (Dicentrarchus labrax, L.), although this is one of the most important species in Mediterranean aquaculture. These considerations prompted our interest in cloning the GR in this species and investigating the impact of long-term exposure to crowding stress on GR expression in the liver of sea bass. Our data clearly demonstrate that a high rearing density stress affects GR mRNA, whose abundance in the liver decreased inversely with blood cortisol levels.

Cortisol receptor blockade and seawater adaptation in the euryhaline teleost Fundulus heteroclitus

To examine the role of cortisol in seawater osmoregulation in a euryhaline teleost, adult killifish were acclimated to brackish water (10 per thousand) and RU486 or vehicle was administered orally in peanut oil daily for five days at low (40 mg.kg(-1)) or high dose (200 mg.kg(-1)). Fish were transferred to 1.5 x seawater (45 per thousand) or to brackish water (control) and sampled at 24 h and 48 h after transfer, when Cl- secretion is upregulated. At 24 h, opercular membrane Cl- secretion rate, as Isc, was increased only in the high dose RU486 group. Stimulation of membranes by 3-isobutyl-1-methylxanthine and cAMP increased Isc in vehicle treated controls but those from RU486-treated animals were unchanged and membranes from brackish water animals showed a decrease in Isc. At 48 h, Isc increased and transepithelial resistance decreased in vehicle and RU486 groups, compared to brackish water controls. Plasma cortisol increased in all groups transferred to high salinity, compared to brackish water controls. RU486 treated animals had higher cortisol levels compared to vehicle controls. Vehicle treated controls had lower cortisol levels than untreated or RU486 treated animals, higher stimulation of Isc, and lower hematocrit at 24 h, beneficial effects attributed to increased caloric intake from the peanut oil vehicle. Chloride cell density was significantly increased in the high dose RU486 group at 48 hours, yet Isc was unchanged, suggesting a decrease in Cl- secretion per cell. Thus cortisol enhances NaCl secretion capacity in chloride cells, likely via glucocorticoid type receptors.

Influence of cortisol on osmoregulation and energy metabolism in gilthead seabream Sparus aurata

Gilthead seabream Sparus aurata were injected intraperitoneally with slow-release implants of coconut oil alone or containing cortisol (50 and 100 microg x g(-1) body weight), and sampled after two, five, and seven days to assess the simultaneous effects of cortisol on both osmoregulation and energy metabolism. Plasma cortisol levels increased in treated fish to 50-70 ng x ml(-1). An enhanced hypoosmoregulatory capacity of cortisol-implanted fish is suggested by the increase observed in gill Na+, K+-ATPase activity, and the decrease observed in plasma ion concentration (Na+ and Cl-) and osmolality. Cortisol also elicited metabolic changes in liver (increased gluconeogenic potential suggested by elevated FBPase activity, and decreased potential of glycolysis and pentose-phosphate shunt, suggested by the decreased activities of both PK and G6PDH) supporting changes in levels of plasma metabolites suitable for use in other tissues. Thus in this study, we demonstrate for the first time in fish that cortisol treatments elicit changes in the use of exogenous glucose in gills (decreased HK activity) and an increased glycolytic and glycogenic potential in brain (increased GPase, PK and PFK activities).

Stress adaptation, cortisol and pubertal development in the male common carp, Cyprinus carpio

This paper reviews a series of recent studies on the effect of adaptation to chronic stress on pubertal development in the common carp. In pre-pubertal male common carp adaptation to temperature stress caused a retardation of testicular development. Stress-induced delay of the first wave of spermatogenesis could be prevented by treatment with a cortisol antagonist, indicating that the stress effect is mediated by cortisol. Chronically elevated cortisol levels affected all parts of the brain-pituitary-gonad (BPG)-axis. In the hypothalamus lower levels of sGnRH were observed, in the pituitary the steady state levels of FSHbeta-m RNA were decreased, while the testicular production of especially the 11-oxygenated androgens 11-ketoandrostenedione (OA) and 11keto-testosterone (11KT) was strongly diminished. OA and 11KT have been shown to promote testicular development in fish. The LH-induced androgen synthesis in vitro was strongly inhibited by cortisol and its agonist dexamethasone. Although cortisol was shown also to interfere with the synthesis of the 11-oxygenated androgens in vivo, the lower androgen levels induced by cortisol were mainly due to the reduced testicular mass. Restoration of the plasma concentrations of these androgens by implantation could not prevent the cortisol-induced retardation of testicular growth and the first wave of spermatogenesis. Therefore, it is suggested that cortisol acts directly on Sertoli cells and/or on germ cells, which is supported by the demonstration of GRs on germ cells. We have little indication that the cortisol-induced retardation of testicular development is mediated by a decreased secretion of LH, but a crucial role for FSH can not be excluded.

Evidence for a mineralocorticoid-like receptor linked to branchial chloride cell proliferation in freshwater rainbow trout

Fish acclimated to ion-deficient water exhibit proliferation of branchial chloride cells. The objective of the present study was to investigate the role of cortisol in this response using the corticosteroid receptor antagonists RU486 and spironolactone. RU486 is a potent antagonist of the glucocorticoid actions of cortisol, whereas spironolactone exhibits high-affinity binding to mineralocorticoid receptors, with a resulting blockade of mineralocorticoid properties in mammals. Untreated rainbow trout, as well as rainbow trout given a single intraperitoneal implant of coconut oil alone, coconut oil containing RU486 (0.5 mg g–1) or coconut oil containing spironolactone (0.1 mg g–1), were exposed to either dechlorinated city-of-Ottawa tapwater or artificial softwater for 7 days. Neither corticosteroid antagonist nor acclimation condition affected circulating plasma cortisol levels, plasma ion concentrations or gill Na+-K+-ATPase activity. Kidney Na+-K+-ATPase activity was significantly higher in softwater-acclimated fish than in fish held in dechlorinated tapwater. In addition, whereas RU486 treatment was found to be without effect on gill morphometrics, treatment with spironolactone inhibited the proliferation of chloride cells normally associated with acclimation to ion-deficient water. The results of the present study provide further evidence for the mineralocorticoid actions of cortisol in freshwater fish, specifically in eliciting chloride cell proliferation. Furthermore, these results support the hypothesis that distinct glucocorticoid and mineralocorticoid receptor populations are present in teleost fish, despite the apparent absence of the classic mineralocorticoid hormone, aldosterone.

Localization of cortisol receptor in branchial chloride cells in chum salmon fry

To clarify the involvement of cortisol in functional differentiation of branchial chloride cells, cellular gene expression and localization of cortisol receptor were examined in chum salmon (Oncorhynchus keta) fry in freshwater (FW) and those adapted to seawater (SW) by in situ hybridization and immunocytochemical staining. Sodium-potassium adenosinetriphosphatase (Na+,K(+)-ATPase) activity in the whole gill homogenate was significantly higher in SW fish than in FW fish. There were no significant differences in plasma cortisol levels nor in the expression of cortisol receptor mRNA, examined by Northern blot analysis, between SW and FW fish. The receptor gene expression, examined by in situ hybridization with biotin-labeled synthetic oligonucleotide probe, and specific immunostaining with anticortisol receptor serum were found in two types of chloride cells distributed in the gill filaments and lamellae, which were also labeled with anti-Na+,K(+)-ATPase serum, indicating that cortisol may be one of the important factors regulating chloride cell functions. Gene expression of cortisol receptor in filament chloride cells, which were highly activated in SW-adapted fry, was significantly greater in the fry adapted to SW than in FW-adapted fry, reflecting their specific role in salt secretion in SW. Cortisol receptors were also present in undifferentiated cells in the interlamellar regions adjacent to the central venous sinus, also suggesting the involvement of cortisol in the functional differentiation of chloride cells.

Partial cloning of the hormone-binding domain of the cortisol receptor in tilapia, Oreochromis mossambicus, and changes in the mRNA level during embryonic development

Cortisol is one of the central hormones in osmoregulation in fish, especially in seawater adaptation. A cDNA of 453 bp was cloned from liver mRNA of freshwater-reared tilapia (Oreochromis mossambicus), by reverse transcription polymerase chain reaction (RT-PCR) with primers designed for the hormone-binding domain of glucocorticoid receptors (GRs) in mammals and rainbow trout. The sequence of PCR product has 83% homology to the trout GR at the nucleotide level and 92% at the amino acid level. The PCR product of tilapia showed highest homology (74% at the amino acid level) to GR among human steroid hormone receptors, including mineralocorticoid receptor. The length of the receptor mRNA of tilapia was about 6.5 kb as determined by Northern blot hybridization. The mRNA concentration in the gills was relatively higher among various organs, the highest concentration being observed in blood cells. Signal intensity of the receptor message in the gills was stronger in fish reared in freshwater than in those reared in seawater or in concentrated (160%) seawater. During early development of tilapia, the highest concentration of receptor mRNA in the total RNA extracted from the whole egg was found just after fertilization, and its concentration decreased steadily toward hatching. The absolute amount of receptor mRNA per egg increased gradually before the initiation of cortisol production by the embryo. When embryos were transferred from fresh water to seawater 2 days before hatching, no difference was observed in the signal intensity of the receptor mRNA among embryos after 1, 2 (the day of hatching), 4, and 7 days.

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

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.