Kisspeptin induction of somatolactin- alpha release in goldfish pituitary cells: functional role of cAMP/PKA-, PLC/PKC-, and Ca super( 2+)/calmodulin-dependent cascades

Although the importance of kisspeptin in the pituitary is firmly established, the signaling mechanisms for the pituitary actions of kisspeptin are still largely unknown. Somatolactin (SL), a member of the growth hormone (GH)/prolactin (PRL) family, is a pituitary hormone with pleiotropic functions in fish, but its regulation by kisspeptin has not been examined. To investigate the functional role of kisspeptin in SL regulation, expression of two paralogues of goldfish Kiss1 receptors (Kiss1ra and Kiss1rb) were confirmed in immunoidentified SL... but not SL... cells isolated by RT-PCR coupled with laser capture microdissection. In goldfish pituitary cells prepared from neurointermediate lobe (NIL), synthetic goldfish Kiss decapeptides (gKiss1-10 and gKiss2-10) could increase SL... release. Consistent with the lack of Kiss1r expression in SL... cells, SL... release was not altered by kisspeptin stimulation. In parallel experiments, goldfish gKiss1-10 could elevate cyclic adenosine monophosphate (cAMP) production, upregulate protein kinase A (PKA) and protein kinase C (PKC) activities, and trigger a rapid rise in intracellular Ca2+ levels in goldfish NIL cells. Using a pharmacological approach, cAMP/PKA and phospholipase C (PLC)/PKC pathways and subsequent activation of Ca2+/calmodulin (CaM)-dependent cascades were shown to be involved in SL... release induced by gKiss1-10. Apparently, the Ca2+-dependent cascades were triggered by extracellular Ca2+ entry via voltage-sensitive Ca2+ channels and mobilization of inositol trisphosphate-sensitive intracellular Ca2+ stores. Our results demonstrate that gKiss1-10 can act directly at the pituitary level to trigger SL... release via a complex network of post-receptor signaling mechanisms. (ProQuest: ... denotes formulae/symbols omitted.)