Vasoactive Intestinal Peptide Concentrations in Turkey Hypophysial Portal Blood Differ across the Reproductive Cycle

Youngren, Orlan M.; Chaiseha, Yupaporn; Phillips, Richard E.; Halawani, Mohamed E. El

doi:10.1006/gcen.1996.0128

Cited by 47 publications

(37 citation statements)

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“…Our findings show that, after an initial slow rate of decrease, the rate of decay of PRL mRNA is significantly faster after adding actinomycin D alone (t ½ =3·7 0·7 h) than after treatment with VIP and actinomycin D (t ½ =26·3 4·3 h). These findings are consistent with our earlier data that showed the half-life of PRL mRNA to be positively correlated with PRL mRNA abundance and VIP release (Youngren et al 1996, Tong et al 1997. Thus, in hyperprolactinemic incubating hens, which have up-regulated steady-state concentrations of PRL mRNA (Wong et al 1992), the half-life of PRL mRNA is longer compared with that of reproductively inactive hypoprolactinemic hens which display reduced PRL mRNA abundance and VIP release (Youngren et al 1996).…”

Section: Discussionsupporting

confidence: 92%

“…Previously, high levels of PRL expression were observed in response to exogenous VIP (Talbot et al 1991, Pitts et al 1994b, Xu et al 1996 and under conditions of an enhanced VIP secretion (Wong et al 1991, Youngren et al 1996. In contrast, VIP immunoneutralization was shown to suppress PRL mRNA steady-state concentrations (Youngren et al 1994).…”

Section: Discussionmentioning

confidence: 96%

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Vasoactive intestinal peptide stimulates turkey prolactin gene expression by increasing transcription rate and enhancing mRNA stability

Tong

Pitts

You

et al. 1998

Journal of Molecular Endocrinology

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This study evaluates the transcriptional and post-transcriptional regulation of prolactin (PRL) by vasoactive intestinal peptide (VIP). Pituitary nuclei from laying (control), incubating (with enhanced VIP secretion), and VIP-immunized laying turkey hens, and from pituitary cells cultured with or without VIP were used in nuclear run-on transcription assays. Cytoplasmic PRL mRNA was analyzed by slot blot hybridization. PRL transcription was greater in hyperprolactinemic incubating birds (PRL/ -actin=3·33) than in laying birds (PRL/ -actin=1·83). VIP-immunoneutralized birds had 47% and 51% decreases in PRL transcription and cytoplasmic PRL mRNA, respectively when compared with laying birds. In primary pituitary cell cultures, VIP significantly increased the transcription rate of PRL (3·8-fold) and cytoplasmic PRL mRNA (3·2-fold) compared with that of non-VIP-treated pituitary cells. The stability of pre-existing PRL mRNA was measured by Northern blot analysis after addition of actinomycin D. PRL mRNA half-lives were calculated using a two-component model, with a first-long component of 18·0 1·0 h and a second-short component of 3·7 0·7 h in non-VIP-treated pituitary cells. Both half-lives were significantly increased (53·2 6·9 and 26·3 4·3 h) in VIP-treated cells. The present data show that VIP acts to stimulate PRL expression by up-regulating the transcription rate of PRL and by enhancing PRL mRNA stability.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 96%

Vasoactive intestinal peptide stimulates turkey prolactin gene expression by increasing transcription rate and enhancing mRNA stability

Tong

Pitts

You

et al. 1998

Journal of Molecular Endocrinology

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“…It appears that DA is inhibitory to the neuroendocrine system which stimulates PRL secretion in laying hens, while in incubating hens, the dopaminergic inhibition is diminished, allowing for the increased PRL levels observed during incubation [8]. Photorefractory turkey hens have VIP content levels in median eminence tissue and in CSF as great as or greater than those observed in incubating hens, yet their circulating PRL levels are as low as or lower than that of laying hens [35]. Dopaminergic inhibition at the pituitary level may play a role in this discrepancy.…”

Section: Discussionmentioning

confidence: 99%

Regulation of Prolactin Secretion by Dopamine and Vasoactive Intestinal Peptide at the Level of the Pituitary in the Turkey

1998

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This study investigated the capability of dopamine (DA) to prevent avian prolactin (PRL) secretion by antagonizing the PRL-releasing factor, vasoactive intestinal peptide (VIP), at the level of the pituitary. To test this hypothesis, combined intracranial and intrapituitary infusions of DA, DA agonists, and VIP, plus electrical stimulation of the medial preoptic area (ES/POM), were used to characterize the actions of DA on PRL secretion in anesthetized laying turkey hens. Infused into the third ventricle at the rate of 10 nmol/min, DA induced a 2.8-fold increase in circulating PRL levels (63.8 ± 15.1 to 181.3 ± 44.3 ng/ml, p < 0.05), similar to the 3.1-fold PRL increase induced by ES/POM (65 ± 10.3 to 199.1 ± 57.3 ng/ml, p < 0.05). Infused into the anterior pituitary at the rate of 15 ng/min, VIP induced a 2.2-fold increase in PRL (78.6 ± 22.9 to 173.6 ± 39.5 ng/ml, p < 0.05). When DA (10 nmol/min) was infused into the anterior pituitary it completely blocked both ES/POM- and VIP-induced PRL secretion. The D₂ DA receptor agonist R- (–) -Propylnorapomorphine HCl inhibited VIP-induced PRL secretion at the level of the anterior pituitary, allowing only an insignificant rise in PRL (54.8 ± 14.3 to 73.9 ± 21.6 ng/ml, p > 0.05), while the D₁ DA receptor agonist (±)-SKF-38393 HCl failed to prevent VIP-induced PRL release, allowing PRL to rise 2.5-fold (49.1 ± 10.8 to 121.0 ± 34.8 ng/ml, p < 0.05). Pituitary infusion of DA, DA agonists or vehicle alone caused no change in PRL levels. The data showed that DA prevented avian PRL secretion by blocking the action of VIP at the level of the anterior pituitary. DA effected this blockade of PRL via D₂ DA receptors residing within the anterior pituitary. The data also suggested that there were no stimulatory D₁ DA receptors related to PRL secretion in the avian anterior pituitary.

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“…Serotonin and ĸ opioid receptors appear to lie above the synapse containing D 1 DA receptors. In birds, the primary PRL-releasing factor (perhaps the only one) released from the hypothalamus into the hypothalamo-pituitary portal vessels is VIP [16, 22]. The ability of dynorphin, 5-HT, and DA to stimulate PRL secretion is contingent upon an intact VIPergic system.…”

Section: Discussionmentioning

confidence: 99%

“…VIP is mobilized from neurons concentrated within the mediobasal hypothalamus that project to the external layer of the median eminence [17, 18, 19, 20, 21]. From the median eminence, VIP is transported via the hypothalamic-pituitary portal blood vessels to the anterior pituitary where it acts on putative VIP receptors located on lactotroph cells [22]. …”

Section: Introductionmentioning

confidence: 99%

An Opioid Pathway in the Hypothalamus of the Turkey That Stimulates Prolactin Secretion

et al. 1999

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Circulating prolactin (PRL) levels increase when dynorphin is infused into the turkey brain. This study tested the hypothesis that centrally infused dynorphin requires an intact vasoactive intestinal peptide (VIP) system in order to stimulate turkey PRL secretion. It also investigated the roles of the dopaminergic and serotonergic systems in dynorphin-induced PRL release. Drugs were infused into the third ventricle of anesthetized laying turkeys via stereotaxically guided cannulae and circulating blood was assayed for changes in PRL levels. When a highly selective ĸ opioid receptor antagonist was given prior to dynorphin injection, the PRL response to dynorphin was almost totally blocked. The coinfusion of either a serotonin (5-HT) or a D₁ dopamine (DA) receptor antagonist with dynorphin prevented the increase in PRL observed in birds when dynorphin was infused alone. On the other hand, the ĸ opioid receptor antagonist failed to prevent the 5-HT-induced release of PRL. In hens actively immunized against VIP, infused dynorphin was unable to increase plasma PRL levels and infused VIP gave a muted PRL rise, while large increases in PRL were seen in nonimmunized birds receiving the same infusions. These data show that: (1) dynorphin stimulates PRL secretion by activating ĸ opioid receptors in the avian hypothalamus, and (2) dynorphin, 5-HT, DA, and VIP stimulate avian PRL secretion via a common pathway expressing ĸ opioid, serotonergic, dopaminergic, and VIPergic receptors at synapses arranged serially in that functional order, with the VIPergic system as the final mediator (releasing factor).

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Vasoactive Intestinal Peptide Concentrations in Turkey Hypophysial Portal Blood Differ across the Reproductive Cycle

Cited by 47 publications

References 0 publications

Vasoactive intestinal peptide stimulates turkey prolactin gene expression by increasing transcription rate and enhancing mRNA stability

Vasoactive intestinal peptide stimulates turkey prolactin gene expression by increasing transcription rate and enhancing mRNA stability

Regulation of Prolactin Secretion by Dopamine and Vasoactive Intestinal Peptide at the Level of the Pituitary in the Turkey

An Opioid Pathway in the Hypothalamus of the Turkey That Stimulates Prolactin Secretion

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