Role and production of secretoneurin (SN) in the goldfish pituitary

Abstract

Secretoneurin (SN) is a 33--34 amino acid neuropeptide derived from secretogranin II (SgII), a protein belonging to the chromogranin family. In static incubation studies, SN (10--500 nM) had a direct effect on pituitary fragments to increase luteinizing hormone (LH) release after 3-hour treatment. SN also induced a specific 2.6-fold increment of LHbeta subunit messenger RNA levels after 6-hour treatment. Using a western blot analysis with a polyclonal rabbit anti-SN antibody, two intermediate proteins (∼57 kDa and ∼30 kDa) likely processed from the 69.6-kDa SgII precursor were detected in the goldfish pituitary. Levels of the ∼57-kDa SN-immunoreactive protein were ∼5-fold higher in the pars distalis than the neurointermediate lobe. In summary, SN has a direct stimulatory action on LH release and synthesis. High production of SN-containing proteins in the pars distalis of the pituitary suggests the existence of a local SN-mediated mechanism to regulate LH in goldfish.