Energy and corticosteroid mobilization following an induced stress response in an elasmobranch fish, the North Pacific spiny dogfish (Squalus acanthias suckleyi)

Abstract

The dominant corticosteroid in elasmobranchs, 1α-hydroxycorticosterone (1α-OHB), has a described role in mineral regulation but a presumptive role in energy balance. Energy demand in vertebrates following exposure to a stressor typically involves an immediate but transient release of glucocorticoids as a means of mobilizing available energy stores, usually in the form of glucose. Although a glucocorticoid role for 1α-OHB would be expected, direct glucocorticoid function of this steroid has yet to be reported in any elasmobranch. In addition, elasmobranchs also utilize the metabolite β-hydroxybutyrate (β-HB), which is thought to replace the role fatty acids play in most vertebrates as a predominant fuel source in extrahepatic tissues. To determine the mobilization of metabolites and corticosteroids during a stress event, North Pacific spiny dogfish, Squalus acanthias suckleyi, were cannulated and held in a darkened isolation box to recover (24-48 h) before being subjected to an acute air exposure or corticosterone injection. Dogfish were then serially blood sampled at nine timepoints over 48 h. Glucose, β-HB, 1α-OHB, corticosterone, as well as lactate, pH, and osmolality were quantified in plasma samples. All measured variables increased in control and treatment groups within 48 h from the start of experimentation, and β-HB and 1α-OHB remained elevated for the duration of the experiment. There was no linear correlation between glucose and 1α-OHB, but there was a weak (R² = 0.230) although significant (p = 0.001), positive correlation between β-HB and 1α-OHB. Interestingly, there were also significant correlations between increasing circulating glucose and corticosterone (R² = 0.349; p < 0.001), and decreasing β-HB and corticosterone concentrations (R² = 0.180; p = 0.008). Our data suggest that following successive stressors of capture, surgery, and confinement, 1α-OHB was not correlated with circulating glucose, only weakly correlated with circulating β-HB concentrations (R² = 0.230; p = 0.001), and that corticosterone may also serve a role in energy mobilization in this species.

Keywords: 1α-hydroxycorticosterone; Corticosteroid; Elasmobranch; Glucose; Metabolism; Stress; β-hydroxybutyrate.