Dopaminergic regulation of avian prolactin gene transcription

Abstract

It is well documented that prolactin (PRL) release and PRL gene expression in birds are controlled by the tonic stimulation of hypothalamic vasoactive intestinal peptide (VIP). However, there is good evidence that dopamine (DA) exerts both stimulatory (at the hypothalamic level) and inhibitory (at the pituitary level) effects on PRL secretion. The interactions between VIP and DA in the regulation of PRL gene transcription are not known. This study was designed to examine the effects of a D 2 DA receptor agonist (D 2 AG; R(−)-propylnorapomorphine HCl) on basal and VIP-stimulated PRL gene transcription rate, PRL mRNA steady-state levels, PRL mRNA stability and PRL release from cultured turkey anterior pituitary cells. The D 2 AG (10 −10 M) completely inhibited the stimulatory effect of VIP (10 −7 M) upon nascent PRL mRNA as determined utilizing a nuclear run-on transcription assay. To examine further the effect of the D 2 AG on PRL mRNA post-transcriptional events, anterior pituitary cells were treated with different concentrations of D 2 AG (10 −12 -10 −4 M). Semi-quantitative RT-PCR and RIA were performed to determine the levels of PRL mRNA and PRL content in the medium respectively. The results show that D 2 AG inhibited VIP-stimulated PRL mRNA steady-state levels as well as basal and VIP-stimulated PRL release, effects which were diminished by the D 2 DA receptor antagonist, S(−)-eticlopride HCl (10 −10 M). Actinomycin D (5 µg/ml), an inhibitor of mRNA synthesis, was used to assess the effect of D 2 AG on PRL mRNA stability in response to VIP. The stimulatory effect of VIP on PRL mRNA stability was completely negated by the D 2 AG (from a half-life of 53·0±2·3 h in VIP-treated cells to 25·5±1·6 h in D 2 AG+VIP-treated cells, P≤0·05). These results support the hypothesis that VIP and DA play a major role in the regulation of PRL gene expression in avian species, at both the transcriptional and post-transcriptional levels. In addition, these findings suggest that the DAergic system inhibits PRL release and synthesis by antagonizing VIP at the pituitary level via D 2 DA receptors.

Transcriptome Profiling Identifies Differentially Expressed Genes in Huoyan Goose Ovaries between the Laying Period and Ceased Period

“…In avian species, two distinct dopamine receptor subtypes, DRD1 and DRD2, have been reported. Dopamine can inhibit PRL secretion via DRD2 at the pituitary level by operating through vasoactive intestinal peptide (VIP) [61]. The DRD2 gene is widely distributed in the hypothalamic-pituitary-ovarian axis of chickens, turkeys and geese, and it plays an important role in the regulation of hormone secretion and reproductive behaviors [62], [63], [64].…”

Dopamine and prolactin involvement in the maternal care of chicks in the native Thai hen (Gallus domesticus)

“…DA exerts stimulatory effects on PRL secretion via the D 1 DA receptor subtype, whereas it exerts inhibitory effects via the D 2 DA receptor subtype (Al Kahtane et al, 2003;Chaiseha et al, 1997Chaiseha et al, , 2003. In turkeys, high expression of D 1 DA receptor mRNA is found in the hypothalamus of hyperprolactinemic incubating hens and in the pituitary glands of laying hens, whereas high expression of D 2 DA receptor mRNA is observed in the pituitary glands of hypoprolactinemic photorefractory hens Schnell et al, 1999).…”

Polymorphisms associated with egg number at 300 days of age in chickens

“…VIP is a well-known hypothalamic PRL-releasing factor in avian (El Halawani et al, 1996) and its physiological effects are mediated through activating its specific receptor (Chaiseha et al, 2004). Furthermore, dopamine was demonstrated to play a dual role in PRL release by affecting VIP secretion, exerting its inhibitory effect via dopamine D2 receptor (DRD2) (Al Kahtane et al, 2003). Therefore, GnRH-I, GnRHR, NPY, PRL, VIP and one of its receptors, VIPR-1, as well as DRD2 were regarded as candidates of chicken EN300 in this study.…”