VASOACTIVE-INTESTINAL-PEPTIDE STIMULATES PROLACTIN MESSENGER-RNA EXPRESSION IN TURKEY PITUITARY-CELLS - EFFECTS OF DOPAMINERGIC DRUGS

It is well documented that vasoactive intestinal peptide (VIP) is a pr olactin (PRL)-releasing factor and that dopamine (DA) is an inhibitory neurotransmitter in avian species, However, the roles of VIP and DA i n the regulation of PRL gene expression are unclear, In this study, pr imary anterior pituitary cells cultured from laying turkeys were utili zed to investigate the influence of VIP and dopaminergic D-1 and D-2 r eceptors on PRL secretion, PRL mRNA, and PRL synthesis, Incubation of pituitary cells with VIP increased PRL secretion up to 3.5-fold within 3 hr, Prolactin mRNA was undetectable during the first 2 hr of pituit ary cell treatment; thereafter, the PRL mRNA content response to VIP i ncreased within 24-48 h (P < 0.05), Total PRL content (media + cellula r) increased over time in the presence of VIP, The response of cells i ncubated in the presence of a dopaminergic D-1 receptor agonist (SKF38 393) was variable and inconclusive, However, cells incubated with a do paminergic D-2 receptor agonist (quinpirole) inhibited VIP-induced PRL secretion (P < 0.05) and PRL mRNA levels (P < 0.05) in a dose-related fashion without effect on the basal levels of PRL release and PRL mRN A, These observations suggest that VIP, in addition to acting as a PRL -releasing peptide, also plays a role in the regulation of PRL gene ex pression, Moreover, the results of this study also indicate that a dru g that can selectively stimulate dopamine D-2 receptors can also regul ate PRL secretion and PRL mRNA in turkey pituitary cells in culture.