Secretoneurin stimulates goldfish pituitary luteinizing hormone production

Secretoneurin (SN), a 33-34 amino acid neuropeptide is derived from endoproteolysis of secretogranin II (SgII), a member protein of the chromogranin family. SN is widely distributed in various tissues of vertebrates especially in pituitary and hypothalamus, and is a potential new hormone. In vivo, i.p. injection of SN increased luteinizing hormone (LH) release in goldfish pretreated with the dopamine antagonist domperidone. In 6-h static incubation of goldfish pituitary fragments, 10 and 100 nM but not 1 nM concentrations of goldfish SN had a direct stimulatory effect to increase LH release by 2.3- and 1.5-fold (p < 0.05), respectively. In addition, 500 nM SN induced a 2.6-fold increase in LHβ subunit messenger RNA (mRNA) levels in pituitary fragments, regardless of whether LHβ mRNA levels were expressed relative to 18S ribosomal RNA or β-actin mRNA. We suggest that the stimulatory actions of SN on LH release may be a part of a paracrine or autocrine feedback loop in the pituitary.