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 metabo lic rate, marine teleost. The objective of this study was to determine i) whether cortisol implantation (50 mg.kg-1) for 7 days altered hepa tocyte metabolism, and hepatocyte responsiveness to epinephrine, gluca gon and insulin, and ii) whether 8 weeks of food-deprivation modified the above response. Cortisol implantation significantly increased hepa tocyte total glucose production and oxidation from alanine compared to the sham group. There was no cortisol effect on glycogen breakdown, s uggesting that the activation of other pathways, including gluconeogen esis, are required to account for the increased glucose production. Ep inephrine-mediated (10(-5)M) glycogen breakdown and insulin-mediated ( 10(-8)M) total glucose production were enhanced in hepatocytes of cort isol implanted sea ravens, but there were no change in any glucagon (1 0(-7)M) effects. The enhanced glycogen breakdown in the absence of sim ilar 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 t otal glucose production and flux rates from alanine increased signific antly with food-deprivation. Moreover, food-deprivation increased resp onsiveness of total hepatocyte glucose production to the actions of gl ucagon 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 e ffect 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.