PI3K signalling in GnRH actions on dispersed goldfish pituitary cells: Relationship with PKC-mediated LH and GH release and regulation of long-term effects on secretion and total cellular hormone availability

Goldfish pituitary cells are exposed to two GnRHs, salmon (s)GnRH and chicken (c)GnRH-II. Phosphoinositide 3-kinase (PI3K) and protein kinase C (PKC) both participate in acute sGnRH- and cGnRH-II-stimulated LH and GH release. Using goldfish pituitary cells, we examined the relationship between PI3K and PKC in acute LH and GH secretion, and PI3K involvement in chronic hormone release and total LH and GH availability. The PI3K inhibitor LY294002 did not affect PKC agonists-induced LH or GH release, and PKC agonists did not alter PI3K p85 phosphorylation, suggesting PKC activation is not upstream of PI3K in acute hormone release. In 2, 6, 12 and 24 h treatments, LY294002 did not affect LH release but stimulated total LH availability at 6 h. sGnRH stimulatory actions on LH release and total availability at 12 and 24 h, and cGnRH-II effects on these parameters at 6 h were inhibited by LY294002. LY294002 enhanced basal GH release at 2 and 6 h, but reduced total GH at 12 and 24 h. Increased GH release was seen following 6, 12 and 24 h of sGnRH, and 2, 6 and 24 h of cGnRH-II treatment but total GH availability was only elevated by 24 h cGnRH-II treatment. Whereas LY294002 inhibited GH release responses to sGnRH at 12 h and cGnRH-II at 6 h, it attenuated cGnRH-II-elicited, but not sGnRH-induced, effects on total GH. These results indicate that PI3K differentially modulates long-term basal and GnRH-stimulated hormone release, and total hormone availability, in a time-, cell-type-, and GnRH isoform-selective manner.