Investigating energy balance and hormonal influence in an elasmobranch fish the North Pacific spiny dogfish, Squalus suckleyi
Appropriate energy balance is fundamental for survival, particularly when the demand for energy increases, such as activation of the endocrine stress axis in vertebrates. Hormonal control of energy balance is critical for fueling the stress response and to reestablish internal equilibrium. In most vertebrates, glucose is a predominate fuel source and is primarily mobilized following a stress event. Elasmobranchs are considered relatively glucose intolerant, in comparison to mammals, and also use ketone bodies (e.g. 3-hydroxybutyrate [3-HB]) extrahepatically as a fuel source in both satiated and starved conditions; thus, it is plausible that elasmobranchs use ketones to fuel the stress response. This thesis aims to investigate energy balance (specifically balance of the energy metabolites: glucose and 3-HB) and hormonal regulation during the stress response using a holistic approach in a representative elasmobranch species, the North Pacific spiny dogfish, Squalus suckleyi, by 1) examining metabolite and corticosteroid mobilization in vivo following a stress event, 2) assessing changes in metabolite balance following hormonal stimulation is a novel in situ liver perfusion, and 3) exploring cellular enzymatic and molecular mechanisms involved in metabolite balance. Data presented here show that metabolite mobilization and usage is likely context-dependent and that S. suckleyi is slow to mobilize and use the fuel sources investigated. Further, there is evidence presented that demonstrate an increase in measured plasma corticosteroids following a stress event, but that this is not repeatable across different stressors. However, this thesis highlights hormonal candidates that may serve a role in regulating energy balance, such as 11-deoxycortiosterone. Ultimately, this thesis demonstrates that glucose and 3-HB may serve to fuel the stress response in the relative long-term, but the identity of the hormones that regulate balance of these metabolites remains elusive.
shark, elasmobranch, metabolism, endocrinology, hormone