Progestins actions in the lactotroph population: mPR involvement in PRL secretion

CAMILLETI, MARIA ANDREA; THOMAS, PETER; FARAONI, ERIKA; FERRARIS JIMENA; ABELEDO-MACHADO, ALEJANDRA; DIAZ-TORGA, GRACIELA

Congreso; FASEB-GROWTH HORMONE/PROLACTIN FAMILY IN BIOLOGYN AND DISEASE; 2017

In the pituitary, therole of progesterone (P4) in controlling lactotroph proliferation and prolactin(PRL) secretion remains unclear. It has been described that concomitant P4treatment prevented both the elevation of plasma PRL level and development ofprolactinomas in chronically-estrogen treated rats. In contrast, female miceexpressing hCGβ with enhanced LH action and high progesterone levels displayedpituitary prolactinomas. We hypothesize that these controversial results of P4actions on PRL secretion are due to the different hormonal milieu and the progesteronereceptor types involved. Two receptor types mediate progestin actions: thenuclear progestin receptors (nPRs) and the membrane progestin receptors (mPRs).The mPRs (α, β, γ, δ, ε) are novel 7-transmembrane-G protein coupled receptorswhich have been shown to mediate rapid, non-genomic progesterone actions indifferent cell types.                                                                      Inour present work, the relative expression of nPRs and mPRs assayed by qRT-PCR inpituitary glands of Sprague Dawley (SD) female rats in diestrus showed that nPRscorrespond to 86% while mPRs represented the 14%. The relative expression of mPRa mRNA was the highest among all the mPRs in the pituitary gland (41%)followed by mPRb and mPRε. mPRa expression in lactotrophs was proved by Immunohistochemical analysis ofrat pituitaries sections showing positive fluorescent staining of both PRL and mPRαproteins. Approximately 54% of total pituitary cells were mPRa+ and among them 65% were lactotrophs according to flow cytometry analysis.In order to determine mPR involvement in PRL secretion two functional assayswere conducted with a selective mPR agonist, 10-ethenyl-19-norporgesterone OrgOD 02-0 (OD). In an ex vivoexperiment, pituitaries from female SD rats were incubated with 100 nM OD.After 1 h incubation with OD, PRL secretion (measured by RIA) decreasedsignificantly (486,8 ± 27,8 ng/ml OD vs 700 ± 20,3 ng/ml Ctrl, p=0.006). Concomitantly,the pituitary content of active TGFβ1, a known inhibitor of lactotroph functionsignificantly increased with OD (OD 56,74 ± 8,12 pg/mg protein vs Control29±0,84, p=0.009; measured by ELISA). A similar experiment was carried out in vitro using the GH3 somalactotrophcell line. Interestingly, OD (100nM) decreased PRL levels after 30 min, 1 h and6 h treatment while this effect was not observed with nuclear PR agonist R5020(10nM).                      This studyprovides the first evidence of mPRs function in the pituitary gland. Takentogether, our results suggest a role for mPRs in progestin actions in thelactotroph population through the inhibition of PRL secretion.