A putative corticosteroid hormone in Pacific lamprey, Entosphenus tridentatus

• 11-Deoxycortisol is present in Pacific lamprey plasma.
• 11-Deoxycortisol levels increase 30 min after exposure to stress.
• 11-Deoxycortisol levels increase after injections of sea lamprey CRH peptide.
• Sea lamprey ACTHs do not display any stimulatory effects on 11-deoxycrotisol levels.

Great efforts have been put forth to elucidate the mechanisms of the stress response in vertebrates and demonstrate the conserved response across different vertebrate groups, ranging from similarities in the activation of the hypothalamic–pituitary–adrenal axis to the release and role of corticosteroids. There is however, still very little known about stress physiology in the Pacific lamprey (Entosphenus tridentatus), descendants of the earliest vertebrate lineage, the agnathans. In this paper we demonstrate that 11-deoxycortisol, a steroid precursor to cortisol in the steroidogenic pathway, may be a functional corticosteroid in Pacific lamprey. We identified the putative hormone in Pacific lamprey plasma by employing an array of methods such as RIA, HPLC and mass spectrometry analysis. We demonstrated that plasma levels of 11-deoxycortisol significantly increased in Pacific lamprey 0.5 and 1 h after stress exposure and that lamprey corticotropin releasing hormone injections increased circulating levels of 11-deoxycortisol, suggesting that the stress response is under the control of the HPA/I axis as it is in higher vertebrates. A comprehensive understanding of vertebrate stress physiology may help shed light on the evolution of the corticosteroid signaling system within the vertebrate lineage.