Endocrine Abstracts

Hypothalamic neuropeptide PACAP is a potent endogenous stimulator of adenylate cyclase synthesis in gonadotrope cells. Previously we found that, in contrast to GnRH, also Cu–GnRH complex is able to induce cAMP/PKA pathway activity.

The aim of the study was to determine whether Cu–GnRH can act via GnRH-R and/or PAC-1 receptors to stimulate cAMP/PKA intracellular signaling. Moreover, we compared PACAP and Cu–GnRH ability to activate cGMP/PKG system in anterior pituitary cells.

5×105/ ml cells obtained from cycling female rats were preincubated for 72 h and then stimulated for 30 min, 1 and 3 h by 10⁻⁷ M of Cu–GnRH or PACAP. Peptides were also incubated with cells pretreated with 5× 10⁻⁷ M of specific receptor antagonists: PACAP 6–38 (for PAC-1 receptor) or antide (for GnRH receptor). Intracellular and extracellular cAMP, cGMP and LH medium concentration were measured by specific RIAs.

PACAP as well as Cu–GnRH activated cAMP synthesis although pattern of activation was different for both peptides. PACAP-induced increase in cAMP concentration was detected after 30 min, whereas Cu–GnRH -induced elevation required 1 h of incubation. In contrast to Cu–GnRH, PACAP-stimulated cAMP/PKA pathway activity remained time-dependent since an increase of cAMP concentration was found up to 3 h of incubation. cAMP synthesis was reduced when Cu–GnRH complex was incubated in the presence of PAC-1 receptor antagonist but was not changed in the presence of GnRH receptor antagonist. Obtained data also revealed that Cu–GnRH potently stimulated cGMP synthesis and inhibition of endogenous PKA activity resulted in an inhibition of cGMP production in anterior pituitary cells.

In conclusion, results indicate that Cu–GnRH-induced cAMP/PKA pathway activation might occur, at least partially, through an involvement of specific PACAP receptor. Moreover, Cu–GnRH complex may induce a cross-talk between cAMP/PKA and cGMP/PKG pathways in anterior pituitary cells.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.