Cobalt complex with GnRH stimulates the LH release and PKA signaling pathway in pig anterior pituitary cells in vitro

Metal complexes with GnRH were shown to interact with GnRH receptors in pituitary cells. In the present study we examined the effects of GnRH and its cobalt complex form (Co-GnRH) on LH secretion and generation of second messengers, namely inositol phosphates (IPs) and cAMP, in porcine pituitary cells in vitro. The cells were obtained from gilt pituitary at the pre-ovulatory phase of estrous cycle and cultured for 72 h before challenge with GnRH or Co-GnRH. Both substances induced a significant increase in LH release that was detectable after 60 min (P < 0.05) of treatment, with the Co-GnRH complex being more efficient than GnRH at 180 min (P < 0.01). GnRH and Co-GnRH were equally effective at 10−8 M (P < 0.01), however, at the lowest (10−9 M) as well as the highest (10−7 M) concentrations tested, Co-GnRH was more potent than its native counterpart (P < 0.01). Interestingly, Co-GnRH revealed twice more efficient than GnRH at stimulating cAMP production, an effect which was detectable in cells after 1 h-incubation (P < 0.001). In contrast, while native GnRH induced a rapid increase (P < 0.05) in IPs no such effect of Co-GnRH was observed. These data demonstrate that Co-GnRH and GnRH differentially effect on the signaling pathway in porcine gonadotropes and suggest that in these cells, the releasing action of Co-GnRH results from the mediation via the cAMP/protein kinase A second messenger system.