Using specific antisera to neutralize ACTH in sturgeon: a method for manipulating the interrenal response during stress.

Abstract Interrenal function and the magnitude of the stress response were assessed in green sturgeon ( Acipenser medirostris ) passively immunized with antisera directed against adrenocorticotropic hormone (ACTH). The nucleotide sequence encoding ACTH was determined using reverse transcriptase polymerase chain reaction (RT-PCR). We identified two isoforms of ACTH that differ at a single site (position 26) in the 39 AA peptide. Both forms of green sturgeon ACTH (gsACTH 1–39 ) display 100% homology with both sequences of white sturgeon ACTH (wsACTH 1–39 ). The N-terminal portion of gsACTH also shares absolute identity with the comparable portion of human ACTH (hACTH). However, we identified considerable sequence divergence in the C-terminal domain between gsACTH and hACTH. Species-specific anti-ACTH sera were generated by vaccinating sheep against the C-terminal portion of gsACTH (gsACTH 26–39 ). The peptide was covalently linked to a carrier protein (keyhole-limpet-hemocyanin [KLH]) to further enhance its immunogenicity. The anti-gsACTH sera recognized gsACTH 1–39 and the immunogenic peptide (gsACTH 26–39 ), but did not interact with hACTH 1–39 . To assess the impact of the antisera, fish were passively immunized with anti-gsACTH 26–39 sera or anti-KLH sera and challenged with a hACTH 1–39 injection on day 1 followed by a 1-min air emersion stressor on day 2. The magnitude and duration of the secretory response induced by hACTH did not differ ( P  > .05) between groups. Conversely, the magnitude of cortisol secretion induced by air emersion was significantly attenuated ( P 26–39 . Collectively, these data demonstrate that the targeted antisera used in this study can discriminate between mammalian and green sturgeon ACTH and moderate the in vivo response to a stressor.