Evidence for cortisol production in a shark.

Corticosteroids are essential regulators of numerous physiological functions in vertebrates, including energy balance, immune responses, osmotic balance and metabolism. The terminal corticosteroids are highly conserved across jawed vertebrates, where cortisol or corticosterone mediates these physiological responses. Elasmobranchs, however, have a unique dominant circulating steroid, 1⍺-hydroxycorticosterone, and since its discovery it has been presumed that elasmobranchs do not produce cortisol. Here, we demonstrate that cortisol is produced by North Pacific spiny dogfish (Squalus suckleyi). For the first time to our knowledge, we confirm the presence of transcripts encoding Cyp17 (which produces steroid intermediates of cortisol) in the interrenal tissue. We provide evidence of circulating cortisol in dogfish following two experimental methods: recovery from a hypoosmotic challenge (48 h at 21 ppt) and a 5-day gavage of antibiotics. Finally, cortisol implants at physiologically relevant levels were used to determine putative glucocorticoid and/or mineralocorticoid roles. Broadly, a persistent depression of plasma glucose occurred with implantation while little effect was seen on plasma osmolytes, yet definitive roles remain elusive. Together, we demonstrate context-dependent cortisol production in an elasmobranch and that endogenous cortisol at this level exerts a glucoregulatory effect. Further, our findings support a novel hypothesis for microbial steroid biosynthesis in elasmobranchs.