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 epinephrine-stimulated glucose release in perfused trout liver was studied. Thermally acclimated (5 and 20°C) rainbow trout (Oncorhynchus mykiss) were responsive to epinephrine (0.5×10-6 mol l-1) at both 5 and 20°C. Metoprolol (beta2 antagonist) and propranolol (beta1and2) decreased the response significantly (to 1.4 % and 8.4 % of stimulated values, respectively) while phentolamine (alpha1and2) was without effect, implying the response is beta2-mediated. Both basal (86 and 19 micromole g-1 liver h-1 in 5 and 20°C trout, respectively) and epinephrine-stimulated (210 and 168 micromole g-1 h-1) rates of glucose release were higher (2.4-fold higher for epinephrine-stimulated and 8.8-fold for basal) in 5°C- than in 20°C-acclimated fish, regardless of perfusion temperature. Although the dose-response curve for epinephrine was markedly temperature-dependent, cold- and warm-acclimated fish were affected in different ways. Cold-acclimated fish (5°C) were less responsive to epinephrine when perfused at 5°C (ED50 6.8×10-9 mol l-1) than when perfused at 20°C (ED50 8.2×10-10 mol l-1); in contrast, warm-acclimated fish (20°C) were less responsive to epinephrine when perfused at 20°C (ED50 4.6×10-7 mol l-1) than at 5°C (ED50 6.6×10-9 mol l-1). These results are interpreted as being indicative of adaptations to maintain the capacity for hepatic glucose mobilization at low temperature.
In the field: an interview with Martha Muñoz
Martha Muñoz is an Assistant Professor at Yale University, investigating the evolutionary biology of anole lizards and lungless salamanders. In our new Conversation, she talks about her fieldwork in Indonesia, Costa Rica, the Dominican Republic and the Appalachian Mountains, including a death-defying dash to the top of a mountain through an approaching hurricane.
Graham Scott in conversation with Big Biology
Graham Scott talks to Big Biology about the oxygen cascade in mice living on mountaintops, extreme environments for such small organisms. In this JEB-sponsored episode, they discuss the concept of symmorphosis and the evolution of the oxygen cascade.
Trap-jaw ants coordinate tendon and exoskeleton for perfect mandible arc
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Trap-jaw ants run the risk of tearing themselves apart when they fire off their mandibles, but Greg Sutton & co have discovered that the ants simultaneously push and pull the mandibles using energy stored in a head tendon and their exoskeleton to drive the jaws in a perfect arc.
Hearing without a tympanic ear
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In their Review, Grace Capshaw, Jakob Christensen-Dalsgaard and Catherine Carr explore the mechanisms of hearing in extant atympanate vertebrates and the implications for the early evolution of tympanate hearing.
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