Epinephrine Stimulation of Glucose Release from Perfused Trout Liver: Effects of Assay and Acclimation Temperature

Since fish are poikilothermic, changes in temperature may perturb hormonal activation of cell function. To test this hypothesis, and determine the extent to which hormonal responses are thermally compensated, the effect of temperature on epinephrinestimulated glucose release in perfused trout liver was studied. Thermally acclimated (5 and 20 ̊C) rainbow trout (Oncorhynchus mykiss) were responsive to epinephrine (0.531026 mol l–1) at both 5 and 20 ̊C. Metoprolol (b2 antagonist) and propranolol (b1and2) decreased the response significantly (to 1.4% and 8.4% of stimulated values, respectively) while phentolamine (a1and2) was without effect, implying the response is b2-mediated. Both basal (86 and 19mmol g21 liver h21 in 5 and 20 ̊C trout, respectively) and epinephrine-stimulated (210 and 168 mmolg21 h21) rates of glucose release were higher (2.4-fold higher for epinephrine-stimulated and 8.8-fold for basal) in 5 ̊Cthan in 20 ̊C-acclimated fish, regardless of perfusion temperature. Although the dose–response curve for epinephrine was markedly temperature-dependent, coldand warm-acclimated fish were affected in different ways. Cold-acclimated fish (5 ̊C) were less responsive to epinephrine when perfused at 5 ̊C (ED50 6.831029 mol l–1) than when perfused at 20 ̊C (ED50 8.2310210 mol l–1); in contrast, warm-acclimated fish (20 ̊C) were less responsive to epinephrine when perfused at 20 ̊C (ED50 4.631027 mol l–1) than at 5 ̊C (ED50 6.631029 mol l–1). These results are interpreted as being indicative of adaptations to maintain the capacity for hepatic glucose mobilization at low temperature.