Dopamine Inhibits Basal Prolactin Release in Pituitary Lactotrophs through Pertussis Toxin-Sensitive and -Insensitive Signaling Pathways

Abstract

Dopamine D2 receptors signal through the pertussis toxin (PTX)-sensitive G(i/o) and PTX-insensitive G(z) proteins, as well as through a G protein-independent, beta-arrestin/glycogen synthase kinase-3-dependent pathway. Activation of these receptors in pituitary lactotrophs leads to inhibition of prolactin (PRL) release. It has been suggested that this inhibition occurs through the G(i/o)-alpha protein-mediated inhibition of cAMP production and/or G(i/o)-betagamma dimer-mediated activation of inward rectifier K(+) channels and inhibition of voltage-gated Ca(2+) channels. Here we show that the dopamine agonist-induced inhibition of spontaneous Ca(2+) influx and release of prestored PRL was preserved when cAMP levels were elevated by forskolin treatment. We further observed that dopamine agonists inhibited both spontaneous and depolarization-induced Ca(2+) influx in untreated but not in PTX-treated cells. This inhibition was also observed in cells with blocked inward rectifier K(+) channels, suggesting that the dopamine effect on voltage-gated Ca(2+) channel gating is sufficient to inhibit spontaneous Ca(2+) influx. However, agonist-induced inhibition of PRL release was only partially relieved in PTX-treated cells, indicating that dopamine receptors also inhibit exocytosis downstream of voltage-gated Ca(2+) influx. The PTX-insensitive step in agonist-induced inhibition of PRL release was not affected by the addition of wortmannin, an inhibitor of phosphatidylinositol 3-kinase, and lithium, an inhibitor of glycogen synthase kinase-3, but was attenuated in the presence of phorbol 12-myristate 13-acetate, which inhibits G(z) signaling pathway in a protein kinase C-dependent manner. Thus, dopamine inhibits basal PRL release by blocking voltage-gated Ca(2+) influx through the PTX-sensitive signaling pathway and by desensitizing Ca(2+) secretion coupling through the PTX-insensitive and protein kinase C-sensitive signaling pathway.

Dynamic organisation of prolactin gene expression in living pituitary tissue

“…Dopamine acts in vivo to suppress PRL gene transcription (Elsholtz et al, 1991) and lactotroph proliferation through dopamine D2 receptors (Ben-Jonathan and Hnasko, 2001) and inhibits the secretion of PRL (Gonzalez-Iglesias et al, 2008) in all lactotroph subtypes in both male and female rats (Christian et al, 2007). We hypothesised that the transient increase in luciferase expression detected over the initial 25 hours of imaging in culture conditions resulted from the removal of the tissue from the in vivo tonic inhibition by dopamine.…”

Effects of postnatal bromocriptine injection on thyroid function and prolactinemia of rats at adulthood

“…Besides, thyroid hormones exert important role in thermogenesis (Pétervári et al, 2005;Silva, 2011). All these hormones are influenced by dopamine (Kaptein et al, 1980;Gonzalez-Iglesias et al, 2008;Ustione and Piston, 2012;Alvarez-Aguilar et al, 2013), so it is plausible that improper neonatal dopaminergic stimulation may permanently alter some of these hormones parameters, explaining the observed changes in food consumption and metabolism.…”

Secretoneurin stimulates the production and release of luteinizing hormone in mouse LβT2 gonadotropin cells

“…The L␤T2 cells was preincubated with serum-free DMEM for 15 min and then changed to DMEM with 100 nM mGnRH-A and/or 100 nM SN and incubated for 0.5 h. The intracellular and extracellular cAMP level was determined as described previously (10,17,36). Total cAMP level is the sum of the intracellular and extracellular cAMP levels.…”

“…Given that mouse L␤T2 cells also release SN-immunoreactive peptides, SN may be part of an paracrine and/or autocrine mechanism regulating LH release. 10 , D-Leu 6 , Pro-NHEt 9 )-LHRH] was purchased from Bachem Bioscience (King of Prussia, PA). The 33-amino acid mouse SN (mSN) peptide was synthesized on Fmoc-PAL-PEG polystyrene solid support by using an automated peptide synthesizer (Pioneer; PEPerSeptive Biosystems, Framingham, MA) following HATU/DIEAmediated Fmoc chemistry and purified by reversed-phase HPLC (2).…”