Chicken Vasoactive Intestinal Peptide Research Articles

Vasoactive intestinal peptide promotes differentiation and clock gene expression in granulosa cells from prehierarchal follicles.

Vasoactive intestinal peptide (VIP) signaling via cyclic adenosine monophosphate (cAMP) is reported to stimulate steroidogenesis in ovarian granulosa cells from a variety of vertebrate species, including the domestic hen. Prior to follicle selection in the hen ovary (i.e., cyclic recruitment) follicle-stimulating-hormone (FSH)-induced cAMP signaling is absent within the granulosa layer until immediately following follicle selection. As a consequence, granulosa cells remain in an undifferentiated state and are unable to initiate FSH-induced steroidogenesis. VIP receptors (VPAC1 and VPAC2), like the FSH receptor, are G protein-coupled receptors, so we predicted that VIP signaling in granulosa cells is also absent in follicles that have not yet been selected into the preovulatory hierarchy. Initial studies established that mRNA encoding VPAC1 and VPAC2 are expressed within the granulosa cells throughout follicle development. Nevertheless, undifferentiated granulosa cells from prehierarchal (6-8 mm) follicles do not accumulate cAMP in response to a 4-hr incubation with chicken VIP; the capacity for such receptor signaling is attained only following selection within actively differentiating granulosa cells. VIP treatment did, however, increase expression of mRNA encoding the Gallus circadian clock protein, BMAL1-but only in granulosa cells collected from selected follicles. These findings provide evidence that, at follicle selection, the acquisition of VIP-induced cAMP cell signaling helps initiate and promote the differentiation of of granulosa cells. Furthermore, we propose that VIP signaling may regulate BMAL1 expression and, thus, a daily rhythmicity within granulosa cells of preovulatory follicles. Mol. Reprod. Dev. 83: 455-463, 2016. © 2016 Wiley Periodicals, Inc.

Role of the serotonergic axis in the reproductive failure associated with aging broiler breeder roosters

Reproductive failure associated with aging is a well-known phenomenon. However, the mechanism by which this failure occurs in broiler breeder roosters is still unclear. A previous study conducted in our laboratory, comparing young and aging broiler breeder roosters, demonstrated an elevation in hypothalamic vasoactive intestinal peptide (VIP) and pituitary prolactin (PRL) gene expression accompanied by a deterioration of gonadal axis function. This resulted in a decrease in semen-quality variables as roosters aged. The objective of this study was to examine the involvement of the serotonergic axis in the age-associated reproductive failure in broiler breeder roosters. Cobb roosters aged 64 wk were divided into 3 groups (n = 20 each): parachlorophenylalanine (PCPA) administration, active immunization against chicken VIP, and controls. At 69 wk of age, each group was divided into 2 equal subgroups: 1 received ovine PRL and the other served as controls. Weekly semen volume, concentration and motility, and plasma testosterone, estradiol, and PRL concentrations were examined. At the end of the experiment, roosters were euthanized, testes were weighed, and hypothalamus and pituitary were removed to assay the expression of genes encoding hypothalamic GnRH-I, pituitary FSH, pituitary LH, hypothalamic VIP, and pituitary PRL. Both PCPA administration and active immunization against chicken VIP significantly increased testis weight, semen volume, sperm concentration, ejaculation grade, plasma testosterone level, and GnRH-I, FSH and LH gene expression compared with controls (P ≤ 0.05). In addition, a decrease in plasma estradiol and PRL concentrations and VIP and PRL gene expression was observed in PCPA- and VIP-immunized birds compared with controls (P ≤ 0.05). Administration of PRL in all groups decreased gonadal axis function and semen-quality variables (P ≤ 0.05). Collectively, these results suggest that the increasing expression levels of the serotonergic axis in aging broiler breeder roosters inhibit proper gonadal function and reproductive performance. This article establishes for the first time the inhibitory role of serotonin on reproduction in aging roosters.

Feeding response following central administration of chicken vasoactive intestinal peptide in chicks

Vasoactive intestinal peptide (VIP) is expressed in central nervous systems and peripheral tissues across lower and higher vertebrates and is involved in many physiological functions. One of these functions is appetite regulation; however the mechanisms mediating this response are poorly understood. Therefore, the purpose of this study was to investigate central mechanisms of VIP induction of satiety using chicks as models. Intracerebroventricular (ICV) injection of VIP (0.1 and 0.5nmol) significantly decreased food intake under both ad libitum and food deprivation conditions and chicken VIP (cVIP) was more potent than mammalian VIP. The mechanisms involved with the VIP-induced anorexigenic effect were investigated by studying the involvement of the central corticotrophin-releasing hormone (CRH) systems. ICV injection of cVIP caused increased plasma corticosterone concentration and decreased diencephalic mRNA expression of CRH, CRH receptor-2 (CRH-R2) and urocortin 3 (UCN-3, which has high affinity for CRH-R2). This simultaneous decrease in the expression of ligands and their receptor, with the increase in plasma corticosterone concentration suggests that the anorexigenic effect of cVIP might be related to CRH systems. The cVIP-induced anorexigenic effect was partly attenuated by co-injection of astressin, a CRH-R2 antagonist, supporting this thesis. The present study demonstrated that VIP inhibits feeding behavior via CRH systems in the brain of chicks.

Associations between polymorphisms in the chicken VIP gene, egg production and broody traits

1. In this study, the vasoactive intestinal peptide (VIP) gene was screened for variations by cloning and sequencing to analyse the association with chicken egg production and broodiness traits. 2. Sequencing revealed that 69 polymorphisms were found in a 9305-bp length of the chicken VIP gene, of which 39 were located in introns, 28 in 5′ regulatory region, 1 in exon 6 (synonymous) and 1 in 3′-UTR. The nucleotide diversity corrected for sample size was 1·96 × 10−3. 3. Five polymorphisms, C-3134T, “AGG” indel at −2648 to −2650, C + 338T, G + 780T and A + 4691G, were genotyped in 644 individuals of Ningdu Sanhuang chickens to evaluate their effects on egg production and broodiness traits. Marker-trait association analyses showed that the “AGG” indel was associated with total number of eggs from 90 to 300 d of age and total number of qualified eggs from 90 to 300 d of age. In contrast, C + 338T was associated with duration of broodiness.

Distribution of vasoactive intestinal peptide and substance P messenger ribonucleic acid in intestinal nerve of Remak of chicken

The intestinal nerve of Remak (INR) is unique to birds. The exact distributions and secretions of the peptide transmitters in the INR that innervate the intestine, and the patterns of their projections to the nerve plexus of the intestinal wall, are still unclear. In the present study, the distributions of chicken vasoactive intestinal peptide (VIP) mRNA and substance P (SP) mRNA in the chicken INR were demonstrated by means of in situ hybridization histochemistry, using sense and antisense digoxigenin-labeled RNA probes. The in situ hybridization histochemistry results suggested that VIP mRNA-positive neurons were mainly distributed in ganglions, whereas some of the INR fibers were weakly positive. The proportion of VIP mRNA-positive cells among total neurons was 75% in the juxta-jejunoileum portion and 87% in the juxta-rectal portion of the INR. Most SP mRNA-positive cells were sporadically distributed in layers or small groups within the ganglions, as well as in nerve trunks between ganglions. Moreover, the proportion of positive cells among total neurons was 83% in the juxta-jejunoileum portion and 98% in the juxta-rectal portion of the INR, which suggests that both VIP and SP mRNA are coexpressed in the chicken INR. Our results provide an approach to further study of the locations of VIP and SP in nerve tissue.

Immunization Against Vasoactive Intestinal Peptide and its Effects on Prolactin, Steroid, Luteinizing Hormone and Egg Production During Mid Laying Cycle in Punjab Brown (PB3 ) Birds

Objective of the study is examine the effects of active immunization against chicken Vasoactive Intestinal Peptide (chVIP) on plasma prolactin (PRL) concentration, concentration of luteinizing hormone (LH) profile its interval and duration, Progesterone (P ), Estradiol (E s), intersequence pause days and egg 4 2 production in birds during the later stages of egg production from 48-72 weeks of egg lay in PB3 birds. Twenty-four PB3 birds of same age group were divided into 2 groups of 12 in each. Birds in control group were administered s/c with placebo. Equal volume of chVIP immunogenic protein was administered to treated group from 17 week of age to 36 weeks of age at an interval of 4 weeks. Hormonal profiles of th immunized and control birds were quantified at weekly intervals from 48th to 72nd weeks of age in both the groups for prolactin, LH, estradiol, progesterone. Egg production and pause days were recorded in both the groups. At 59th weeks of age, blood samples from chVIP immunized and control birds were obtained every 4 h for 48 h to study the surges of LH. In immunized PB3 birds (against ch VIP) plasma PRL concentration was lower (p<0.01) with high concentrations of E s, P , LH and its 4 h LH surges in plasma. Significantly 2 4 (p<0.01) higher egg production (13.62%) and less pause days were observed in chVIP immunized birds. It is mainly attributed due to low PRL concentration, associated with high concentrations of LH (with regular interval and duration of LH surges), Es and P concentration required for egg formation and subsequent 2 4 ovulation. In conclusion, chVIP immunization advanced the LH surges, for release of matured oocyte, egg formation and egg lay enabled the birds to lay eggs at regular intervals due to active immunization against chVIP. Results indicate that control of chVIP may lead to more egg production with shorter duration of LH surges.

Prolactin, Luteinizing Hormone and Steroid Hormone Concentration in Punjab Brown (PB3) Birds Immunized Against Vasoactive Intestinal Peptide During the Early Stages of Egg Production

This study aims at the effects of active immunization against chicken Vasoactive Intestinal Peptide (chVIP) on plasma prolactin (PRL) concentration, concentration of Luteinizing Hormone (LH) profile its interval and duration, progesterone (P ), estradiol (E s), intersequence pause days and egg production in 4 2 birds during the initial stages of egg production from 20-36 weeks of egg lay in PB3 birds. Twenty-four PB3 birds of same age group were divided into two groups of twelve in each. Birds in control group were administered s/c with placebo. Equal volume of chVIP immunogenic protein was administered to treate d group from 17th week of age to 36 weeks of age at an interval of four weeks. Hormonal profiles of immunized and control birds were quantified at weekly intervals from 17th to 36th weeks of age in both the groups for prolactin, LH, estradiol, progesterone. Egg production and pause days were recorded in both the groups. At 31st weeks of age, blood samples from chVIP immunized and control birds were obtained every 4 h for 48 hours to study the surges of LH. In immunized PB3 birds (against ch VIP) plasma PRL concentration was lower (p<0.01) with high concentrations of E s, P , LH and, its 4h LH surges, in plasma (p<0.01). Significantly 2 4 higher egg production (9.71%), less pause days were observed in chVIP immunized birds. It is mainly attributed due to low PRL concentration, associated with high concentrations of LH (with regular interval and duration of LH surges), E s and P concentration required for egg formation and subsequent ovulation. In 2 4 conclusion, chVIP immunization advanced the LH surges, for release of matured oocyte, egg formation and egg lay enabled the birds to lay eggs at regular intervals due to active immunization against chVIP. Results indicate that control of chVIP may lead to more egg production with shorter duration of LH surges.

Cyclic AMP Formation in C6 Glioma Cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) exert their actions via common receptors, VPAC1 and VPAC2, which are equally sensitive to both peptides, while PACAP stimulates its specific PAC1-type receptors. Both peptides potently stimulate cAMP production in different biological systems. In the present article, we examined the effects of PACAP and VIP on cAMP formation in C6 rat glioma cells used between passages 12-28 (early) and 120-136 (late). In the presence of the PDE inhibitor IBMX (0.1 mM), PACAP (0.1 microM) and VIP (1 microM) strongly stimulated cAMP synthesis in C6 cells in early passages, but not in C6 cells in late passages. In contrast, forskolin (10 microM), a direct activator of adenylyl cyclase, and isoprenaline (10 microM), a beta-adrenergic receptor agonist, strongly stimulated cAMP production in both early and late C6 cell passages. Concentration-dependent studies carried out in early passages with PACAP-38, PACAP-27, mammalian and chicken VIPs, and PHI/PHM peptides (1-5 microM) revealed that both forms of PACAP produced strong cAMP accumulation, VIP peptides were less effective than PACAP, while the cAMP effects of PHI/PHM peptides were noticeable only at the highest doses tested. These results suggest that C6 glioma cells in early passages possess functional PAC1 and possibly VPAC-type receptors, but either the density of PACAP/VIP receptors progressively declines or the PACAP/VIP receptor-Gs protein coupling becomes less effective through culture passages.

Active Immunization Against cVIP and It`s Role on the Pattern of Sequence Length and Pause Days in Domestic Hen (Gallous domesticus)

Chicken vasoactive intestinal peptide (cVIP) is a hypothalamic PRL (PRL) releasing factor in birds and it plays an important role avian reproduction. Our objective was to determine whether active immunization against cVIP would increase the sequence length, decrease intersequence pause days, and there by improving egg production in White Leghorn (WLH) by decreasing the prolactin (PRL) concentration during the active period of productive cycle in birds. WLH birds at 13 weeks of age were divided into two experimental groups consisting of 21 birds in control and immunized birds. At 17 week of age, 21 birds th were immunized with synthetic chicken VIP (conjugated with keyhole limpet haemocyanin KLH-cVIP), followed by three booster doses at four weekly intervals with a total of four immunizations. Controls were given placebo in place of immunogen. cVIP antibody titers were consistent till the age of 72 weeks in immunized birds. Active immunization of the birds against cVIP significantly (P<0.01) decreased the circulating PRL during and after the withdrawal of immunizations and PRL levels were found to decrease up to the age of 72 weeks of age, resulting in significantly lower incidence of shorter sequences, with significantly (P<0.01) lower number of intersequence pause days, egg laying sequence lengths in bird s immunized against cVIP. Total number of pause days were significantly reduced in immunized birds compared to controls. Egg production increased by 7.00% in the immunized birds over the control birds with the available resources under normal husbandry practices. It is observed that the laying pauses are mainly due to fluctuations in the concentration of PRL above physiological levels in circulation and keeping the PRL hormone under check will influence egg production, pause days, sequence length, persistency in eg g production with almost an egg a day. It is conclude that the physiological pauses that occur during ovulatory sequences can be disrupted effectively using active immunization against cVIP, which modulates PRL levels, that may interfere with the follicular recruitment and subsequent oviposition thereby improving egg production in white leghorn hens.

Receptors for VIP and PACAP in Guinea Pig Cerebral Cortex: Effects on Cyclic AMP Synthesis and Characterization by &lt;SUP&gt;125&lt;/SUP&gt;I-VIP Binding

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in guinea pig cerebral cortex were characterized by (1) radioreceptor binding of 125I-labeled VIP (human/rat/porcine), and (2) cyclic AMP (cAMP) formation. Saturation analysis of 125I-VIP binding to membranes of guinea pig cerebral cortex resulted in a linear Scatchard plot, suggesting the presence of a single class of high-affinity receptor-binding sites, with a Kd of 0.63 nM and a B(max) of 77 fmol/mg protein. Various peptides from the PACAP/VIP/secretin family displaced the specific binding of 125I-VIP to guinea pig cerebrum with the relative rank order of potency: chicken VIP (cVIP) > or = PACAP38 approximately PACAP27 approximately guinea pig VIP (gpVIP) > or = mammalian (human/rat/porcine) VIP (mVIP) > peptide histidine-methionine (PHM) > peptide histidine-isoleucine (PHI) > secretin. Analysis of the competition curves revealed displacement of 125I-VIP from high- and lower-affinity binding sites, with IC50 values in the picomolar and the nanomolar range, respectively. About 70% of the specific 125I-VIP-binding sites in guinea pig cerebral cortex were sensitive to Gpp(NH)p, a nonhydrolyzable analog of GTP. Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38), PACAP27, cVIP, gpVIP, mVIP, PHM, and PHI stimulated cAMP production in [3H]adenine-prelabeled slices of guinea pig cerebral cortex in a concentration-dependent manner. Of the tested peptides, the most effective were PACAP38 and PACAP27, which at a 1 microM concentration produced a 17- to 19-fold rise in cAMP synthesis, increasing the nucleotide production to approx 11% conversion above the control value. The three forms of VIP (cVIP, mVIP, and gpVIP) at the highest concentration used, i.e., 3 microM, produced net increases in cAMP production in the range of 8-9% conversion, whereas 5 microM PHM and PHI, by, respectively, 6.7% and 4.9% conversion. It is concluded that cerebral cortex of guinea pig contains VPAC- type receptors positively linked to cAMP formation. In addition, the observed stronger action of PACAP (both PACAP38 and PACAP27), when compared to any form of VIP, on cAMP production in this tissue, suggests its interaction with both PAC1 and VPAC receptors.

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in turkey cerebral cortex: characterization by 6125I9-VIP binding and effects on cyclic AMP synthesis

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in turkey cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [125I]-VIP, and (2) effects of peptides from the PACAP/VIP/secretin family on cyclic AMP formation. The binding of [125I]-VIP to turkey cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of high affinity receptor binding sites with a Kd of 0.70 nM and a Bmax of 52 fmol/mg protein. Various peptides displaced the specific binding of 0.12 nM [125I]-VIP to turkey cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to turkey cerebrum was: PACAP38 ≈ PACAP27 ≈ chicken VIP ≈ mammalian VIP ⋙ PHI ≫ secretin, chicken VIP16-28 (inactive). About 65% of specific [125I]-VIP binding sites in turkey cerebral cortex was sensitive to Gpp(NH)p, a nonhydrolysable analogue of GTP. PACAP38, PACAP27, chicken VIP and, to a lesser extent, mammalian VIP potently stimulated cyclic AMP formation in turkey cerebral cortical slices in a concentration-dependent manner, displaying EC50 values of 8.7 nM (PACAP38), 21.3 nM (PACAP27), 67.4 nM (chicken VIP), and 202 nM (mammalian VIP). On the other hand, PHI and secretin very weakly affected the nucleotide production. The obtained results indicate that cerebral cortex of turkey contains VPAC type receptors that are positively linked to cyclic AMP-generating system and are labeled with [125I]-VIP.

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in turkey cerebral cortex: characterization by [ 125I]-VIP binding and effects on cyclic AMP synthesis

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in turkey cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [ 125I]-VIP, and (2) effects of peptides from the PACAP/VIP/secretin family on cyclic AMP formation. The binding of [ 125I]-VIP to turkey cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of high affinity receptor binding sites with a K d of 0.70 nM and a B max of 52 fmol/mg protein. Various peptides displaced the specific binding of 0.12 nM [ 125I]-VIP to turkey cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [ 125I]-VIP binding to turkey cerebrum was: PACAP38 ≈ PACAP27 ≈ chicken VIP ≈ mammalian VIP ⋙ PHI ≫ secretin, chicken VIP16-28 (inactive). About 65% of specific [ 125I]-VIP binding sites in turkey cerebral cortex was sensitive to Gpp(NH)p, a nonhydrolysable analogue of GTP. PACAP38, PACAP27, chicken VIP and, to a lesser extent, mammalian VIP potently stimulated cyclic AMP formation in turkey cerebral cortical slices in a concentration-dependent manner, displaying EC 50 values of 8.7 nM (PACAP38), 21.3 nM (PACAP27), 67.4 nM (chicken VIP), and 202 nM (mammalian VIP). On the other hand, PHI and secretin very weakly affected the nucleotide production. The obtained results indicate that cerebral cortex of turkey contains VPAC type receptors that are positively linked to cyclic AMP-generating system and are labeled with [ 125I]-VIP.

Antagonism of VIP-stimulated cyclic AMP formation in chick brain.

Of eight peptides tested (0.01-5 microM), only two, that is, pituitary adenylate cyclase-activating polypeptide (PACAP27) and chicken vasoactive intestinal peptide (cVIP), potently stimulated cyclic AMP (cAMP) production in cerebral cortical slices of the chick. Mammalian VIP (mVIP) showed some activity only at the highest dose tested, whereas truncated forms of PACAP or VIP, that is, PACAP6-27, cVIP6-28, and mVIP6-28, or hybrid compounds, that is, neurotensin6-11-cVIP7-28 (NT-cVIP) and neurotensin6-11-mVIP7-28 (NT-mVIP), were inactive. Thirty-minute preincubation of chick cortical slices with 5 microM PACAP6-27, NT-cVIP, or NT-mVIP competitively antagonized the cAMP effects of cVIP (0.03-1 microM), with the truncated form of PACAP being the best antagonist. Preincubation of slices with 5 microM mVIP6-28 also produced a significant inhibition of the cVIP (0.1-1 microM)-induced increase in cAMP production; however its action was independent of the concentration of cVIP. In contrast to mVIP6-28, cVIP6-28 showed no antagonistic activity against the full-length peptide. In parallel experiments, 30-min pretreatment of cortical slices with 5 microM PACAP6-27 significantly antagonized the PACAP38-evoked increase in cAMP formation, whereas mVIP6-28 or the NT-mVIP hybrid was ineffective. It has been concluded that in the chick brain, PACAP and cVIP stimulate cAMP biosynthesis via PAC1 and VPAC-type receptors, respectively, and PACAP6-27 seems to be the most potent, yet PACAP/VIP receptor-nonselective antagonist. Unlike truncated PACAP, the NT-VIP hybrid peptides tested may represent VPACtype receptor-selective blocking activity.

Effects of Vasoactive Intestinal Peptide on Plasma Prolactin in Passerines

Vasoactive intestinal peptide (VIP) is a potent releaser of prolactin (PRL) in domestic fowl, turkey, and ring doves. However, few comparative studies have investigated this in wild species. We tested the effects of intravenously administered chicken VIP on plasma PRL concentrations in four passerine species: the white-crowned sparrow (Zonotrichia leucophrys gambelii), the dark-eyed junco (Junco hyemalis), the Florida scrub-jay (Aphelocoma coerulescens), and the western scrub-jay (A. californica). In the white-crowned sparrow, junco, and Florida scrub-jay, which were tested during the breeding season, VIP induced a rapid increase in plasma PRL. Serial plasma samples taken after VIP injection in the white-crowned sparrow show a 10-fold increase in PRL within 2 min of treatment, followed by a gradual decline. Effects of VIP, as compared to saline, remained significant for at least 20 min after treatment. Western scrub-jays did not respond to intravenous VIP with a significant rise in PRL secretion, possibly because they were tested after termination of the breeding season. This study indicates that VIP control of PRL release may be widespread among avian species, and that seasonal changes in plasma PRL may be mediated in part at the level of the pituitary. In addition, analysis of the control data revealed no increase in plasma PRL as a result of injection or restraint, suggesting that unlike in mammals, PRL is not released during acute stress in passerines.

Effect of maternal passive immunization against vasoactive intestinal peptide on prolactin secretion in turkey poults.

The purpose of this study was to examine the role of vasoactive intestinal peptide (VIP) in prolactin (PRL) release in young turkey poults. Poults obtained from hens immunized with keyhole limpet hemocyanin (KLH)-chicken VIP (cVIP-KLH) conjugate or with KLH alone were used in this study. Plasma VIP antibody was tested by means of monoiodinated cVIP. Plasma samples were prediluted (1:100) in 0.05 EDTA PBS and used as a source of primary antibody in a cVIP-binding assay. Antibody levels averaged 50.8 +/- 10.3% at hatch and then declined with age to a level of 5.0 +/- 2.1% after 3 wk. Plasma PRL concentration was lower in cVIP-KLH-immunized poults (p < 0.05) than in KLH-immunized birds. Exogenous VIP administration at 7 days of age (7.8 micrograms/kg) increased plasma PRL level (p < 0.05) to a peak value of 359 +/- 32 ng/ml in the KLH-immunized birds. A smaller increase (p < 0.05) was obtained when the KLH-immunized poults received injections at 2 and 3 wk of age. The PRL response to cVIP administration was not observed in 1- and 2-wk-old poults maternally immunized with cVIP-KLH. Similarly, electrical stimulation of the ventromedial nucleus of the hypothalamus, at 1 and 8 days of age, induced a significant increase in the plasma PRL level of maternally KLH-immunized birds but not in maternally cVIP-KLH-immunized birds. These findings suggest that cVIP is a PRL-releasing factor in young turkey poults, similar to the finding in adult turkey hens.

Protein Kinase-C Mediates Chicken Vasoactive Intestinal Peptide Stimulated Prolactin Secretion and Gene Expression in Turkey Primary Pituitary Cells

This set of experiments investigated the role of protein kinase-C (PKC) as a second messenger in vasoactive intestinal peptide (VIP)-stimulated prolactin (PRL) secretion and PRL mRNA abundance. Dispersed anterior pituitary cells (5 × 105 or 106 cells/tube) were isolated from laying turkeys and incubated in 1.0 ml of M-199. In Experiment 1, 10-7M VIP increased PRL secretion three- to fivefold. Prolactin mRNA abundance was higher in VIP-treated cells (11.45 ± 2.11 arbitrary optical unit; AOU) than control cells (4.59 ± 1.2 AOU). In Experiment 2, the addition of 10-12, 10-10, 10-8, and 10-6M phorbol 12-myristate 13-acetate (PMA;PKC agonist) increased PRL release from 8.5 ± 0.7 to 14.9 ± 1.1, 17.2 ± 1.3, 18.1 ± 2.2, and 18.7 ± 2.8 μg/106 cells, respectively. PRL mRNA abundance was significantly (P < 0.01) increased in only 10-6M PMA treatmemt. In Experiment 3, PKC desensitization decreased VIP-stimulated PRL release from 10.0 ± 2.3 to 4.2 ± 0.6 μg/5 × 105 cells and PMA-induced release from 7.1 ± 1.3 to 2.7 ± 0.3 μg/5 × 105 cells. VIP and PMA up-regulated PRL mRNA abundance was decreased two- to fourfold by PKC desensitization. In Experiment 4, 10-6M staurosporine (ST; PKC antagonist) decreased both 10-7M VIP-stimulated PRL secretion from 7.86 ± 2.9 to 2.43 ± 0.5 μg/5 × 105 cells and 10-8M PMA-stimulated PRL secretion from 4.26 ± 0.2 to 2.23 ± 0.3 μg/5 × 105 cells (P < 0.01). In addition, ST decreased VIP-stimulated PRL mRNA abundance from 15.95 ± 2.18 to 11.35 ± 2.27 AOU in VIP- and from 6.36 ± 1.21 to 4.57 ± 0.63 AOU in PMA-treated cells. Intracellular pituitary PRL content did not differ in any treatment (P > 0.05). In conclusion, these results suggest that the PKC second messenger system is involved in VIP-stimulated PRL release and gene expression in primary turkey pituitary cell culture.

Increased Egg Production by Active Immunization against Vasoactive Intestinal Peptide in the Turkey (Meleagris gallopavo)1

Vasoactive intestinal peptide (VIP) is a hypothalamic prolactin (PRL)-releasing factor in the turkey. The hypothesis in the present study was that active immunization of turkeys with VIP would neutralize endogenous VIP, decrease circulating PRI, and consequently prevent the expression of incubation behavior. Large white female turkeys were divided into three experimental groups comprising untreated controls, control turkeys immunized with keyhole limpet hemocyanin (KLH), and turkeys immunized with synthetic chicken VIP conjugate (KLH-cVIP). Each turkey received four injections at 4-wk intervals, starting on the day of photostimulation. The immune response, measured by the percentage binding of monoiodinated chicken VIP (cVIP) to plasma at a dilution of 1:1000, averaged 11.8 +/- 2.5% during the reproductive life cycle. Immunization against KLH-cVIP prevented the normal increases of PRL that are associated with the photo-induced reproductive cycle. Over a 21-wk period beginning at photostimulation, KLH-cVIP-immunized birds exhibited a maximal plasma PRL level of 82.2 +/- 29.5 ng/ml, compared to 367.7 +/- 66.6 ng/ml and 227.5 +/- 51.7 ng/ml for non- and KLH-immunized turkeys, respectively. The total number of nest visits per hen during the 147-day experimental period decreased from 320.0 +/- 48.2 in the nonimmunized controls to 180.7 +/- 53.7 and 149.4 +/- 13.1 visits in KLH- and KLH-cVIP conjugate-immunized turkeys. Turkeys that showed an immune response to KLH-cVIP immunization did not exhibit incubation behavior, whereas 54% and 33% of non- and KLH-immunized hens incubated their eggs.(ABSTRACT TRUNCATED AT 250 WORDS)

Presence of vasoactive intestinal peptide receptor in the hen hypothalamus.

Radioligand assays of the membrane fraction of hen hypothalamic tissues involving the preoptic (HPOA) or median eminence (HMEA) areas revealed the presence of a specific binding component to chicken vasoactive intestinal peptide (cVIP) having properties of a receptor. The equilibrium dissociation constant (Kd) was 0.70 +/- 0.07 nM (Mean +/- SEM; N = 5) in HPOA and 1.02 +/- 0.15 nM (N = 5) in HMEA as estimated by Scatchard analysis of saturation studies, and was 0.91 +/- 0.11 nM (N = 3) (HPOA) and 1.25 +/- 0.09 nM (N = 3) (HMEA) as determined by a kinetic analysis. The maximum binding capacity (Bmax) obtained by Scatchard analysis was 167 +/- 19 fmol/mg protein (N = 5) (HPOA) and 133 +/- 17 fmol/mg protein (N = 5) (HMEA). The Kd and Bmax values obtained by Scatchard analysis were similar in the two areas of the hypothalamus and in both laying and nonlaying hens. Administration of cVIP in vivo caused a decrease in specific cVIP binding. These results suggest the presence of a VIP receptor in the hen hypothalamus.

Sequence of a cDNA encoding chicken vasoactive intestinal peptide (VIP)

Mammalian pre-pro-vasoactive intestinal peptide (pre-proVIP) gives rise to the neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine amide (PHI). The cDNA encoding chicken VIP was cloned and sequenced. The region of chicken pre-proVIP homologous to the mammalian PHI region is not followed by an amidation signal. This unusual feature suggests that processing of the precursor may be different in the chicken.

Active Immunization with Vasoactive Intestinal Peptide Prevents the Secretion of Prolactin Induced by Electrical Stimulation of the Turkey Hypothalamus

Immunoneutralization of endogenous vasoactive intestinal peptide (VIP) by active immunization with chicken VIP (cVIP) reduced both basal circulating prolactin (PRL) and steady-state levels of pituitary PRL mRNA in the turkey. This immunoneutralization severely curtailed the plasma PRL response induced by infusion of cVIP into the median eminence, and totally blocked the plasma PRL release effected by electrical stimulation of the medial preoptic nucleus. This is the first demonstration that a stimulated PRL secretion can be blocked by neutralizing VIP availability. These findings imply that among the neurochemicals released by electrical stimulation, only VIP directly stimulates PRL secretion. In addition to serving as a PRL releasing factor, VIP also appears to be involved in the regulation of pituitary PRL mRNA expression.