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Title: VASOACTIVE INTESTINAL PEPTIDE STIMULATES PROLACTIN MRNA EXPRESSION IN TURKEY PITUITARY CELLS: EFFECTS OF DOPAMINERGIC DRUGS

Author
item XU, M - UNIVERSITY OF MINNESOTA
item Proudman, John
item PITTS, G - UNIVERSITY OF MINNESOTA
item WONG, E - VIRGINIA POLYTECH INST
item FOSTER, D - UNIVERSITY OF MINNESOTA
item EL HALAWANI, M - UNIVERSITY OF MINNESOTA

Submitted to: Society Of Experimental Biological Medicine Proceedings
Publication Type: Other
Publication Acceptance Date: 1/18/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Prolactin (PRL), produced by the pituitary gland, causes incubation behavior and ovarian regression in turkey hens and decreases hatching-egg production. The increase in PRL secretion is caused by vasoactive intestinal peptide (VIP), a brain hormone which acts on the pituitary cell to increase the synthesis and secretion of PRL. In mammals, dopamine, a chemical synthesized by brain cells, inhibits PRL secretion by binding to specific receptors on the pituitary cell. Prior work has shown that dopamine has much less effect on PRL secretion in birds than in mammals. This study was designed to clarify the effects of VIP and dopamine on PRL secretion and on the production of PRL messenger RNA (mRNA) in cultured pituitary cells. The results showed that VIP stimulates synthesis of PRL mRNA 3.5-fold within 3 hours of administration. By using chemicals which block specific types of dopamine receptors, it was determined that binding to the dopaminergic D2 receptor inhibits both PRL mRNA synthesis and VIP- induced PRL secretion. These observations suggest that VIP, in addition to acting as a PRL releasing peptide, also plays a role in the regulation of the PRL gene. A drug which can selectively bind to the dopaminergic D2 receptors can prevent the stimulation of PRL synthesis and secretion in culture. If a similar effect could be produced in turkey hens, this drug may be able to prevent the onset of incubation behavior.

Technical Abstract: It is well documented that vasoactive intestinal peptide (VIP) is a putative prolactin (PRL) releasing factor and that dopamine (DA) is an inhibitory neurotransmitter in avian species. However, the roles of VIP and DA in the regulation of PRL gene expression are unclear. In this study, primary anterior pituitary cells cultured from laying turkeys were utilized to investigate the influence of VIP and dopaminergic D1 and D2 receptors on PRL secretion, PRL mRNA and PRL synthesis. Incubation of pituitary cells with VIP increased PRL secretion up to 3.5-fold within 3 hrs. Prolactin mRNA was undetectable during the first 2 hrs of pituitary cell treatment; thereafter, the PRL mRNA content response to VIP increased within 24 to 48 hrs (P<0.05). Total PRL content (media + cellular) increased over time in the presence of VIP. The response of cells incubated in the presence of a dopaminergic D1 receptor agonist (SKF38393) was variable and inconclusive. However, cells incubated with a dopaminergic D2 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 mRNA. These observations suggest that VIP, in addition to acting as a PRL releasing peptide, also plays a role in the regulation of PRL gene expression. Moreover, the results of this study also indicate that a drug which can selectively stimulate dopaminergic D2 receptor, which is inhibitory to the neuroendocrine system, can also regulate PRL secretion and PRL mRNA in turkey pituitary cells in culture.