Apoptosis of Lactotrophs Induced by D2 Receptor Activation Is Estrogen Dependent

Abstract

BACKGROUND/AIMS: Dopamine (DA) inhibits prolactin release and reduces lactotroph proliferation by activating D2 receptors. DA and its metabolite, 6-hydroxydopamine (6-OHDA), induce apoptosis in different cell types. DA receptors and DA transporter (DAT) were implicated in this action. Considering that estradiol sensitizes anterior pituitary cells to proapoptotic stimuli, we investigated the effect of estradiol on the apoptotic action of DA and 6-OHDA in anterior pituitary cells, and the involvement of the D2 receptor and DAT in the proapoptotic effect of DA. METHODS: Viability of cultured anterior pituitary cells from ovariectomized rats was determined by MTS assay. Apoptosis was evaluated by Annexin-V/flow cytometry and TUNEL. Lactotrophs were identified by immunocytochemistry. RESULTS: DA induced apoptosis of lactotrophs in an estrogen-dependent manner. In contrast, estradiol was not required to trigger the apoptotic action of 6-OHDA. Cabergoline, a D2 receptor agonist, induced lactotroph apoptosis, while sulpiride, a D2 receptor antagonist, blocked DA-induced cell death. The blockade of DAT by GBR12909 did not affect the apoptotic action of DA, but inhibited 6-OHDA-induced apoptosis. CONCLUSION: These data show that DA, through D2 receptor activation, induces apoptosis of estrogen-sensitized anterior pituitary cells, and suggest that DA contributes to the control of lactotroph number not only by inhibiting proliferation but also by inducing apoptosis