Anterior pituitary gland synthesises dopamine froml-3,4-dihydroxyphenylalanine (l-dopa)

Prolactin (PRL) is a hormone principally secreted by lactotrophs of the anterior pituitary gland. Although the synthesis and exocytosis of this hormone are mainly under the regulation of hypothalamic dopamine (DA), the possibility that the anterior pituitary synthesises this catecholamine remains unclear. The present study aimed to determine if the anterior pituitary produces DA from the precursorl-3,4-dihydroxyphenylalanine (l-dopa). Accordingly, we investigated the expression of aromaticl-amino acid decarboxylase (AADC) enzyme and the transporter vesicular monoamine transporter 2 (VMAT2) in the anterior pituitary, AtT20 and GH3 cells by immunofluorescence and western blotting. Moreover, we investigated the production of DA froml-dopa and its release in vitro. Then, we explored the effects ofl-dopa with respect to the secretion of PRL from anterior pituitary fragments. We observed that the anterior pituitary, AtT20 and GH3 cells express both AADC and VMAT2. Next, we detected an increase in DA content after anterior pituitary fragments were incubated withl-dopa. Also, the presence ofl-dopa increased DA levels in incubation media and reduced PRL secretion. Likewise, the content of cellular DA increased after AtT20 cells were incubated withl-dopa. In addition,l-dopa reduced corticotrophin-releasing hormone-stimulated adrenocorticotrophic hormone release from these cells after AADC activity was inhibited by NSD-1015. Moreover, DA formation froml-dopa increased apoptosis and decreased proliferation. However, in the presence of NSD-1015,l-dopa decreased apoptosis and increased proliferation rates. These results suggest that the anterior pituitary synthesises DA froml-dopa by AADC and this catecholamine can be released from this gland contributing to the control of PRL secretion. In addition, our results suggest thatl-dopa exerts direct actions independently from its metabolisation to DA.