Involvement of hypothalamic vasoactive intestinal polypeptide (VIP) in prolactin secretion induced by serotonin in rats

To study the possible involvement of hypothalamic vasoactive intestinal polypeptide (VIP) in regulating the secretion of prolactin (PRL), the effect of anti-VIP rabbit serum on serotonin (5-HT)-induced PRL release was examined in urethane-anesthetized male rats. Anti-VIP serum (AVS) or normal rabbit serum (NRS) was infused into a single hypophysial portal vessel of the rat for 40 min at a rate of 2 microliters/min with the aid of a fine glass cannula and 5-HT was injected into a lateral ventricle 10 min after the start of the infusion. Intraventricular injection of 5-HT (10 micrograms/rat) caused an increase in plasma PRL levels in control animals infused with NRS and 5-HT-induced PRL release was blunted in animals infused with AVS (mean +/- SE peak plasma PRL: 118.9 +/- 19.8 ng/ml vs 54.7 +/- 16.2 ng/ml, p less than 0.05). These findings suggest that the secretion of PRL induced by 5-HT is mediated, at least in part, by hypothalamic VIP release into the hypophysial portal blood in the rat.     

Regulation of somatostatin and growth hormone-releasing factor by gonadal steroids in fetal rat hypothalamic cells in culture.

The mechanism underlying the sexually dimorphic pattern of growth hormone (GH) secretion in the rat has not been clearly elucidated. In the present study, we assayed the possible direct effect of gonadal steroids on both somatostatin (SS) and growth hormone-releasing factor (GRF) in fetal rat hypothalamic cells in culture. Hypothalamic cells, obtained by mechanical dispersion, were maintained as monolayer cultures in serum-supplemented medium. After 20 days in culture, cells were incubated with serum free medium containing testosterone (T, 10, 20, 40 ng/dl) or estradiol (E, 0.1, 1, 10 ng/dl) for 48 h. At the end of the experiments, immunoreactive SS (IR-SS) and immunoreactive GRF (IR-GRF) were measured by specific radioimmunoassays (RIAs) in media and cell extracts. After 48 h of incubation with testosterone, somatostatin in both media and cells was significantly reduced. On the contrary, this treatment lead to a dose-dependent increase in media and cell GRF content. When cells were incubated with estradiol for 48 h, a significant inhibition in medium SS release was observed, whereas intracellular SS slightly increased at the highest concentration of 10 ng/dl. Estradiol treatment resulted in an inconsistent decrease in media and cells IR-GRF. Our results indicate that both SS and GRF are under the influence of testosterone and estradiol acting at the hypothalamic level, and furthermore suggest that at this stage of brain development, gonadal steroids may regulate GH secretion through their ability to modulate hypothalamic SS and GRF.     

Vasoactive intestinal peptide enhances dopamine accumulation in primary cell culture of rat hypothalamus.

The effect of vasoactive intestinal peptide (VIP) and PHI-27 on dopamine accumulation in cultured rat hypothalamic cells was investigated. VIP enhanced [3H]dopamine accumulation dose dependently. This effect was significant at 10(-8)-10(-5) M VIP with a concomitant increase in intracellular cyclic AMP (cAMP), and reached its plateau level at 10(-6) M VIP. VIP increased [3H]dopamine accumulation significantly within 15 min. PHI-27 and dibutyryl cAMP ((Bu)2-cAMP) also enhanced [3H]dopamine accumulation. These results suggest that VIP enhances dopamine accumulation in hypothalamic cells by increasing intracellular cAMP.     

Vasoactive intestinal peptide and forskolin regulate proliferation of the HT29 human colon adenocarcinoma cell line.

Although several lines of evidence implicate cAMP in the regulation of intestinal cell proliferation, the precise role of this second messenger in the control of the human colon cancer cell cycle is still unclear. In order to investigate the role of cAMP in HT29 cell proliferation, we have tested the effect of vasoactive intestinal peptide (VIP) and forskolin on DNA synthesis and cell number, focusing on the time-dependent efficacy of the treatment. The cells were arrested in G0/G1 phase by incubation for 24 h in serum-free medium and proliferation was re-initiated by addition of either 85 nM insulin or 0.5% fetal calf serum. In the presence of fetal calf serum, G1/S transition was found to occur earlier than with insulin. Exposure of the HT29 cells to 10(-5) M forskolin in the early stages of growth induction (within 12 h from FCS addition or within 14 h from insulin treatment) resulted in a significant inhibition of DNA synthesis and a delayed entry in the S phase. By contrast, VIP (10(-7) M) was inhibitory only when added within a narrow window (10 to 12 h or 12 to 14 h following FCS or insulin addition, respectively). The difference in efficiency of forskolin and VIP to inhibit cell proliferation may be correlated with their own potency to promote long-lasting cAMP accumulation. The combination of VIP plus forskolin had synergistic effects on both cAMP accumulation and cell-growth inhibition. Taken together, our data indicate that cAMP may act at a step in the late G1 or G1/S transition.     

Determination of the ovulatory mechanism of the grasscutter (Thryonomys swinderianus)

The objective of this study was to determine whether gonadotrophin-releasing hormone (GnRH), oxytocin (OT) and vasoactive intestinal polypeptide (VIP) modulate beta-endorphin-like immunoreactivity (beta-END-LI) secretion by dispersed anterior pituitary cells of pigs and in vivo priming with steroid hormones, estradiol benzoate (EB) and progesterone (P(4)), influences the cell reactivity to peptide hormones tested. Additionally, the aim of this research was to examine the involvement of cyclic nucleotides (cAMP and cGMP) in transduction of signals induced by GnRH, OT and VIP in porcine pituitary cells. Pituitaries were collected from ovariectomized (OVX) gilts that were divided into four experimental groups. Animals of group 1 (OVX) received 1ml corn oil (placebo)/100 kg body weight (b.w.), group 2 (OVX+EB I) and group 3 (OVX+EB II) were treated with EB at the dose 2.5mg/100 kg b.w., 30-36 and 60-66 h before slaughter, respectively. Animals of group 4 (OVX+P(4)) were injected with P(4) at the dose 120 mg/100 kg b.w. for 5 subsequent days before slaughter. Anterior pituitaries were dispersed with trypsin and then pituitary cells were cultured (10(6) per well) in McCoy's 5A medium containing horse serum (10%) and fetal calf serum (2.5%) for 3 days at 37 degrees C under an atmosphere of 95% air and 5% CO(2). Subsequently, plates were rinsed with fresh McCoy's 5A medium and pituitary cells were treated with one of the following agents: GnRH (100 ng/ml), OT (10(-6)M) or VIP (10(-7)M) and incubated for 3.5h at 37 degrees C.GnRH did not affect beta-END-LI secretion by pituitary cells of OVX (group 1) and OVX+P(4) (group 4) gilts. When the pituitary cells were incubated in the presence of OT and VIP, significant increases were observed. After priming of OVX gilts with EB, 30-36 h before slaughter (group 2), we noted a significant increase in beta-END-LI release from pituitary cells only in the presence of VIP. Pituitary cells from gilts treated with EB, 60-66 h before slaughter (group 3), produced markedly elevated amounts of beta-END-LI after GnRH, OT or VIP addition.GnRH markedly stimulated cGMP release from cultured pituitary cells in all experimental groups and significantly increased cAMP production by the cells from OVX, OVX+EB II and OVX+P(4) animals. The addition of OT enhanced both cAMP and cGMP output in all experimental groups of pigs. VIP stimulated cAMP release from pituitary cells derived from OVX, OVX+EB I and OVX+EB II animals. cGMP output was markedly elevated under the influence of VIP from pituitary cells of OVX, OVX+EB II and OVX+P(4) gilts.In conclusion, our results suggest that GnRH, OT and VIP can modulate beta-endorphin release from porcine pituitary cells and imply the involvement of cAMP and cGMP in transduction of signals induced by studied peptides in the cells.     

Insights into a role of GH secretagogues in reversing the age-related decline in the GH/IGF-I axis

Growth hormone (GH) secretion and serum insulin-like growth factor-I (IGF-I) decline with aging. This study addresses the role played by the hypothalamic regulators in the aging GH decline and investigates the mechanisms through which growth hormone secretagogues (GHS) activate GH secretion in the aging rats. Two groups of male Wistar rats were studied: young-adult (3 mo) and old (24 mo). Hypothalamic growth hormone-releasing hormone (GHRH) mRNA and immunoreactive (IR) GHRH dramatically decreased (P < 0.01 and P < 0.001) in the old rats, as did median eminence IR-GHRH. Decreases of hypothalamic IR-somatostatin (SS; P < 0.001) and SS mRNA (P < 0.01), and median eminence IR-SS were found in old rats as were GHS receptor and IGF-I mRNA (P < 0.01 and P < 0.05). Hypothalamic IGF-I receptor mRNA and protein were unmodified. Both young and old pituitary cells, cultured alone or cocultured with fetal hypothalamic cells, responded to ghrelin. Only in the presence of fetal hypothalamic cells did ghrelin elevate the age-related decrease of GH secretion to within normal adult range. In old rats, growth hormone-releasing peptide-6 returned the levels of GH and IGF-I secretion and liver IGF-I mRNA, and partially restored the lower pituitary IR-GH and GH mRNA levels to those of young untreated rats. These results suggest that the aging GH decline may result from decreased GHRH function rather than from increased SS action. The reduction of hypothalamic GHS-R gene expression might impair the action of ghrelin on GH release. The role of IGF-I is not altered. The aging GH/IGF-I axis decline could be rejuvenated by GHS treatment.     

Responses of human basilar arteries to vasoactive intestinal polypeptide

The responses to 9 X 10(-7) M vasoactive intestinal polypeptide (VIP) by isolated human basilar arteries of 30 individuals were studied to further elucidate the role the peptide might play in modifying cerebrovascular tone normally and in disease. In most experiments the artery was precontracted with prostaglandin F2 alpha (PGF2 alpha), either with 1 or 2 X 10(-6) M or with 10(-5) M PGF2 alpha. The course of action to VIP was observed for 15 min following its application to the contracted vessel. Some arteries failed to respond to VIP (13%), otherwise the arteries relaxed 44% when the contraction was induced by 10(-5) M PGF2 alpha and 67.6% after the lower concentrations of PGF2 alpha. There was no significant decrement in the vasorelaxant effect of VIP throughout the period of observation. A second and third application of VIP to the precontracted artery produced significantly less of an effect than the first, but no consistent progressive pattern of tachyphylaxis was evident. In additional experiments, indomethacin (10(-5) M) did not prevent the vasorelaxant effect of VIP, suggesting that prostanoid synthesis was not involved. Pretreatment of the artery with VIP did not prevent the contractions generated by 10, 30, 50 and 90 mM KCl while antithrombin III (1.2 X 10(-7) M) did, indicating fundamental differences between these two vasorelaxants. In conclusion, VIP will inhibit contraction of isolated human cerebral arteries for prolong periods and could be a significant factor regulating cerebral blood flow in humans.     

Humoral immunity in experimental syphilis: the demonstration of IgG as a treponemicidal factor in immune rabbit serum

The neutralizing activity present in immune rabbit serum (IRS) against virulent Treponema pallidum was shown to be mediated by IgG and complement. IgG was isolated and purified from both IRS and nonimmune rabbit serum (NRS) by the use of an affinity system in which staphylococcal protein A was conjugated to Sepharose 4B. The purity of the isolated IgG fractions was demonstrated by both immunoelectrophoresis and SDS-polyacrylamide gel electrophoresis. Fractions of IgG were tested for specific neutralizing activity as measured by an in vitro-in vivo neutralization test. Lesions failed to develop at 80% of the sites inoculated with treponemal suspensions containing IgG from IRS in the presence of unheated NRS as a source of complement; delayed atypical lesions were observed at the remaining sites. In contrast, typical lesions developed at all sites inoculated with suspensions containing IgG from IRS in the presence of heated NRS. They were significantly delayed, however, as compared with lesion development at control sites inoculated with suspensions containing IgG from NRS. These results provide the first direct evidence for an IgG complement-mediated treponemicidal mechanism operative in immune serum from rabbits with latent syphilis.     

SNV, a lipophilic superactive VIP analog, acts through cGMP to promote neuronal survival.

The current study explored whether the neuroprotective effects of vasoactive intestinal peptide (VIP) and its analog Stearyl-Nle17-VIP (SNV) were mediated through cGMP. SNV, was previously found to be 100-fold more potent than VIP in providing neuroprotection. Neuronal survival was assessed in rat cerebral cortical cultures. A cGMP antagonist (RP-8-pCPT-cGMPS, 10(-12)-10(-9) M) reduced the number of surviving neurons (40-60%), this decline was spared in the presence of SNV (10(-13)M). A cGMP agonist (Sp-8-pCPT-cGMPS, 10(-14)-10(-8)M) and SNV (10(-16)-10(-8)M) both provided significant neuroprotection against 10(-12) M of the cGMP antagonist. Immunoassays indicated that SNV induced increases in cGMP (two-threefold) in these cultures, whereas VIP was 1000-fold less potent. These results implicate cGMP as a second messenger for VIP/SNV-mediated effects on neuronal survival.     

Effect of vasoactive intestinal polypeptide (VIP) on growth hormone (GH) and prolactin (PRL) release and cell morphology in human pituitary adenoma cell cultures

Six GH adenomas and three prolactinomas were investigated by light- and electron-microscopic morphological and immunocytochemical methods and the effect of vasoactive intestinal polypeptide (VIP) on growth hormone (GH) and prolactin (PRL) secretion was tested in vitro. The tumour cells of the acromegalic patients revealed both GH and PRL immunoreactivity while prolactinomas showed only PRL activity. All the adenomas stained immunocytochemically also for VIP. By electron microscopy, the tumours included two densely and two sparsely granulated GH, two mixed GH/PRL, and three sparsely granulated PRL adenomas. The dissociated cells were explanted, and cultured in vitro. The cultures in micro test plates were treated with VIP at different concentrations between 10(-5)-10(-12) M. GH and PRL contents in the culture media were measured by radioimmunoassay. GH release was significantly stimulated by VIP in a dose-dependent manner over the whole concentration range, while VIP was effective on the PRL release only at 10(-6)-10(-7) M concentration. The cells of a mixed adenoma were grown in Petri dishes and used for ultrastructural and immunocytochemical studies. The cytoplasmic structure of the cells treated with VIP corresponded to that of active hormone-secreting cells with large ergastoplasmic fields and Golgi zones containing secretory granules. Massive exocytotic events were encountered mainly in the GH-type cells. GH and PRL double immunocytochemistry showed the predominance of GH cells, many of them containing low amounts of PRL as well. Cells predominantly containing PRL were spread among them, they also might contain GH as well. Some of the cells contained only a single immunoreactive hormone. The intensity of gold labelling of the secretory granules appeared higher in the VIP-treated cells than in the untreated control ones which showed a cytoplasmic structure characteristic of glandular cells with low secretory activity. As all the adenoma cells both contained and reacted to VIP, our results are in agreement with an autocrine or paracrine effect of this peptide. The fine structure of the cells in the cultures treated with VIP supply an additional argument to the assumption that VIP may serve as a growth factor for these cell types.     

Homologous regulation of adenylate cyclase-coupled receptors for vasoactive intestinal peptide (VIP) on human mononuclear leucocytes

The effect of agonists on VIP receptor regulation has been investigated in mononuclear human blood leucocytes. VIP receptor number and affinity, as well as VIP-stimulated cyclic AMP accumulation were measured after pretreatment with VIP, PHM-27 or secretin. Pretreatment for 30 min with 0.1 μM VIP caused 28% (S.E.M. = 15) reduction in specific binding, and 52% (S.E.M. = 12) reduction in cyclic AMP accumulation, while 3 h of pretreatment caused 59% (S.E.M. = 10) and 68% (S.E.M. = 12) reduction. Only VIP concentrations at the nanomolar level and higher were shown to have any effect. B_max of the high-affinity receptor was reduced by 66% (S.E.M. = 8) after 30 min, and 95% (S.E.M. = 3) after 3 h of exposure to 0.1 μM VIP. No significant change was observed in receptor affinity, in B_max of the low-affinity receptor, in ED₅₀, or in ED₁₀₀ of VIP-stimulated cyclic AMP accumulation. Pretreatment with PHM-27 (0.1 μM, 3 h) caused 24% reduction in [¹²⁵I]VIP binding and 25% reduction in cyclic AMP accumulation, while no effect was detected after pretreatment with secretin (0.1 μM, 3 h).     

Dual effect of vasoactive intestinal peptide on the mitogenic response of rabbit spleen lymphocytes

The effects of vasoactive intestinal peptide (VIP) have been investigated on the mitogenic response of rabbit spleen cells. Specific binding of 125I-VIP to these mononuclear cells is rapid and saturable. Analysis of binding reveals two classes of binding sites, a class of high-affinity binding sites with KD = 0.93 +/- 0.11 nM and maximal binding capacity of 2000 +/- 560 sites/cell, and a class of low-affinity binding sites with KD = 225 +/- 58 nM and maximal binding capacity of 280,000 +/- 60,000 sites/cell. The VIP regulatory effect on mitogen-stimulated rabbit spleen cell proliferation appears to be time dependent and bimodal. When VIP was added simultaneously with mitogens, it induced an inhibition of the proliferative response. With concanavalin A (Con A) or pokeweed mitogen (PWM), addition of 10(-8) M VIP resulted in a maximal 30% inhibition of [3H]thymidine incorporation after 96 h of culture. This inhibitory effect was significant at concentrations from 10(-8)-10(-6) M and half-maximal inhibition was obtained with 1.2 x 10(-9) M VIP. By contrast, when rabbit spleen cells were preincubated for 18 h with VIP alone, the lymphocyte proliferative response to Con A was increased. However, this increase was mitogen-selective, since it was only observed when the T-cell mitogen Con A was used. The maximal response was obtained after 96 h of culture in the presence of Con A. The VIP stimulatory effect was dose-dependent with a maximal effect at 10(-7) M and a half-maximal effect at 1.7 x 10(-9) M VIP. The effect of VIP was also time-dependent, since a 6 h preincubation was sufficient to induce a significant increase in the proliferative response which was maximal after an 18 h preincubation.     

Interaction of Neuropeptides and Cultured Glial (Müller) Cells of the Chick Retina: Elevation of Intracellular Cyclic AMP by Vasoactive Intestinal Peptide and Glucagon

Vasoactive intestinal peptide (VIP) and, to a lesser extent, glucagon were found to increase intracellular cyclic AMP rapidly in cultured glial (Müller) cells of the chick embryo retina. Although VIP elicited higher cyclic AMP accumulation than glucagon at each concentration tested, the half-maximal concentrations were similar, i.e., 6 X 10(-8) M for VIP and 8 X 10(-8) M for glucagon. Secretin had a minimal effect on cyclic AMP accumulation even at a very high (5 X 10(-6) M) concentration. Several other peptide and nonpeptide putative agonists also had little effect on cyclic AMP accumulation. The cultured Müller cell may thus be a useful model for examining VIP and glucagon effects on glial elements of the CNS.     

VIP and PACAP stimulate TSH release from the bullfrog pituitary

We have recently shown that corticotropin-releasing hormone (CRH) is a major thyrotropin (TSH)-releasing factor in amphibians, but we have also found that, besides CRH, other hypothalamic substances stimulate TSH secretion in frog. In order to characterize novel TSH secretagogues, we have investigated the effect of frog (Rana ridibunda) vasoactive intestinal polypeptide (VIP) (fVIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) (fPACAP38 and PACAP27) on TSH release from bullfrog (Rana catesbeiana) pituitary cells in primary culture. Incubation of pituitary cells for 24h with graded concentrations of fVIP, fPACAP38 and PACAP27 (10(-9) to 10(-6)M) induced a dose-dependent stimulation of TSH release with minimum effective doses of 10(-9)M for fVIP and 10(-8)M for fPACAP38 and PACAP27. The PAC1-R/VPAC2-R antagonist PACAP(6-38) (10(-7) and 10(-6)M) dose-dependently suppressed the stimulatory effects of fVIP and fPACAP38 (10(-7)M each). Likewise, this antagonist (10(-6) and 10(-5)M) dose-dependently attenuated the stimulatory effect of PACAP27 (10(-7)M). On the other hand, the VPAC1-R/VPAC2-R antagonist [d-pCl-Phe(6), Leu(17)]VIP (10(-6) and 10(-5)M) dose-dependently inhibited the stimulatory effect of fVIP (10(-9)M) and PACAP27 (10(-8)M), but did not affect the response to fPACAP38 (10(-8)M). These data indicate that, in amphibians, the activity of thyrotrophs can be regulated by VIP and PACAP acting likely through VPAC2-R and PAC1-R.     

Isolation of a novel 38 residue-hypothalamic polypeptide which stimulates adenylate cyclase in pituitary cells

A novel neuropeptide which stimulates adenylate cyclase in rat anterior pituitary cell cultures was isolated from ovine hypothalamic tissues. Its amino acid sequence was revealed as: His-Ser-Asp-Gly-Ile-Phe-Thr-Asp-Ser-Tyr-Ser-Arg-Tyr-Arg-Lys-Gln- Met-Ala- Val-Lys-Lys-Tyr-Leu-Ala-Ala-Val-Leu-Gly-Lys-Arg-Tyr-Lys-Gln-Arg-Val-Lys-Asn-Lys - NH2. The N-terminal sequence shows 68% homology with vasoactive intestinal polypeptide (VIP) but its adenylate cyclase stimulating activity was at least 1000 times greater than that of VIP. It increased release of growth hormone (GH), prolactin (PRL), corticotropin (ACTH) and luteinizing hormone (LH) from superfused rat pituitary cells at as small a dose as 10(-10)M (GH, PRL, ACTH) or 10(-9)M (LH). Whether these hypophysiotropic effects are the primary actions of the peptide or what physiological action in the pituitary is linked with the stimulation of adenylate cyclase by this peptide remains to be determined.     

Impact of interleukin-21 in the pathogenesis of primary Sjogren's syndrome: increased serum levels of interleukin-21 and its expression in the labial salivary glands

Introduction

Interleukin (IL)-21 is a cytokine that controls the functional activity of effector T helper cells and the differentiation of Th17 cells, and promotes B-cell differentiation. To test whether IL-21 participates in the pathogenesis of primary Sjögren''s syndrome (SS), serum IL-21 level was measured and IL-21 expression in the labial salivary glands (LSG) was examined.

Methods

Serum IL-21 levels in 40 primary SS, 40 rheumatoid arthritis (RA), and 38 systemic lupus erythematosus (SLE) patients and 20 healthy controls were measured. Serum IL-21 levels of SS patients were assessed for correlations with laboratory data, including anti-nuclear antibody, anti-Ro/La antibodies, globulin, immunoglobulin (Ig) class, and IgG subclass. LSGs from 16 primary SS and 4 controls with sicca symptoms were evaluated for IL-21 and IL-21 receptor (IL-21R) expression by immunohistochemistry. Confocal microscopy was performed to further characterize the IL-21 positive cells.

Results

Primary SS patients had significantly higher serum IL-21 levels than controls, and these increments correlated positively with levels of IgG, IgG1. Serum IgG1 levels correlated with anti-Ro antibody titers. Immunohistochemical analyses showed that lymphocytic foci and the periductal area of the LSGs from SS patients expressed high levels of IL-21 and lower levels of IL-21R, whereas the control LSGs showed minimal expression of both antigens. The more the lymphocyte infiltrated, IL-21expression in LSGs showed a tendency to increase. Confocal microscopic analyses revealed that IL-21 expressing infiltrating lymphocytes in the LSGs of SS patients also expressed CXCR5.

Conclusions

Primary SS is associated with high serum IL-21 levels that correlate positively with serum IgG, especially IgG1, levels. The expression of IL-21 is increased as more lymphocytes infiltrated in LSGs. These observations suggest that IL-21 may play an important role in primary SS pathogenesis.     

The influences of GnRH, oxytocin and vasoactive intestinal peptide on LH and PRL secretion by porcine pituitary cells in vitro.

The aim of the present study was to evaluate the possible direct effects of GnRH, oxytocin (OT) and vasoactive intestinal peptide (VIP) on the release of LH and PRL by dispersed porcine anterior pituitary cells. Pituitary glands were obtained from mature gilts, which were ovariectomized (OVX) one month before slaughter. Gilts randomly assigned to one of the four groups were treated: in Group 1 (n = 8) with 1 ml/100 kg b.w. corn oil (placebo); in Group 2 (n = 8) and Group 3 (n = 8) with estradiol benzoate (EB) at the dose 2.5 mg/100 kg b.w., respectively, 30-36 h and 60-66 h before slaughter; and in Group 4 (n = 9) with progesterone (P4) at the dose 120 mg/ 100 kg b.w. for five consecutive days before slaughter. In gilts of Group 2 and Group 3 treatments with EB have induced the negative and positive feedback in LH secretion, respectively. Isolated anterior pituitary cells (10(6)/well) were cultured in McCoy's 5a medium with horse serum and fetal calf serum for 3 days at 37 degrees C under the atmosphere of 95% air and 5% CO2. Subsequently, the culture plates were rinsed with fresh McCoy's 5A medium and the cells were incubated for 3.5 h at 37 degrees C in the same medium containing one of the following agents: GnRH (100 ng/ml), OT (10-1000 nM) or VIP (1-100 nM). The addition of GnRH to cultured pituitary cells resulted in marked increases in LH release (p < 0.001) in all experimental groups. In the presence of OT and VIP we noted significant increases (p < 0.001) in LH secretion by pituitary cells derived from gilts representing the positive feedback phase (Group 3). In contrast, OT and VIP were without any effect on LH release in Group 1 (placebo) and Group 2 (the negative feedback). Pituitary cells obtained from OVX gilts primed with P4 produced significantly higher amounts (p < 0.001) of LH only after an addition of 100 nM OT. Neuropeptide GnRH did not affect PRL secretion by pituitary cells obtained from gilts of all experimental groups. Oxytocin also failed to alter PRL secretion in Group 1 and Group 2. However, pituitary cells from animals primed with EB 60-66 h before slaughter and P4 produced markedly increased amounts of PRL in the presence of OT. Neuropeptide VIP stimulated PRL release from pituitary cells of OVX gilts primed with EB (Groups 2 and 3) or P4. In contrast, in OVX gilts primed with placebo, VIP was without any effect on PRL secretion. In conclusion, the results of our in vitro studies confirmed the stimulatory effect of GnRH on LH secretion by porcine pituitary cells and also suggest a participation of OT and VIP in modulation of LH and PRL secretion at the pituitary level in a way dependent on hormonal status of animals.     

消化管括约肌部VIP免疫活性神经细胞分布

应用免疫组织化学方法研究了食管下部,幽门和回盲部肌间神经丛内ＶＩＰ免疫活性神经细胞的分布。ＶＩＰ免疫活性神经细胞在括约肌部比相邻部位数量多。并用Ｏｐｅｎ－ｔｉＰ法测量了刺激迷走神经后食管下段括约肌部压力的变化。用高阈值参数电刺激迷走神经引起预先投给阿托品的狗食管下段括约肌部压力的降低;这样条件下延长迷走神经刺激引起肌间神经丛内ＶＩＰ免疫活性神经细胞数量明显增加。由此结果提示含有或产生ＶＩＰ的神经细胞可能接受迷走神经的控制。由于刺激节前迷走神经纤维可能作用到这些细胞。     

Vasoactive intestinal polypeptide (VIP) inhibits rat alveolar macrophage phagocytosis and chemotaxis in vitro.

Vasoactive intestinal polypeptide (VIP) has been shown to inhibit lymphocyte function and is believed to modulate the immune response. We explored the possible immunomodulatory effects of VIP on alveolar macrophage (AM) function by examining its influence on AM phagocytosis and chemotaxis. Rat AMs were collected by bronchoalveolar lavage and incubated for 90 min with polystyrene beads in the presence or absence of VIP in concentrations from 10(-11) M to 10(-5) M. VIP significantly (P less than 0.0001) inhibited AM phagocytosis of polystyrene beads at concentrations of 10(-11) to 10(-6) M, with a maximal inhibition of 35% at 10(-6) M (but no inhibition at 10(-5) M). AMs were also incubated for 90 min in a chemotaxis chamber with endotoxin-activated rat serum (EARS) as a chemoattractant, with or without VIP in concentrations from 10(-9) to 10(-6) M. VIP significantly (P less than 0.0001) inhibited AM chemotaxis by at least 30% at concentrations of 10(-9) to 10(-6) M, with a maximal inhibition of 46% at 10(-7) M. These results indicate that VIP, in concentrations from 10(-11) to 10(-6) M, inhibits rat AM function as assessed by phagocytosis of polystyrene beads and chemotaxis to EARS. The inhibition of alveolar macrophage function is another mechanism by which VIP may modulate the immune response in the lung.     

GABAB Receptor-Mediated Enhancement of Vasoactive Intestinal Peptide-Stimulated Cyclic AMP Production in Slices of Rat Cerebral Cortex

Basal and vasoactive intestinal peptide (VIP)-stimulated accumulations of cyclic AMP were measured in slices of rat cerebral cortex. Neither gamma-aminobutyric acid (GABA) nor the selective GABAB receptor agonist (-)-baclofen stimulated basal cyclic AMP accumulation, whereas VIP caused a large dose-dependent increase in cyclic AMP levels. However, in the presence of 100 microM (-)-baclofen, the effects of VIP on cyclic AMP accumulation were significantly enhanced, with the responses to 1 microM and 10 microM VIP being approximately doubled. The enhancing effects of (-)-baclofen was dose related (1-1,000 microM), but an enhancing effect was not observed with 100 microM (+)-baclofen. In the presence of the GABA uptake inhibitor nipecotic acid (1 mM), GABA caused a similar dose-related enhancement of the VIP response. The ability of either GABA or (-)-baclofen to augment VIP-stimulated production of cyclic AMP was not mimicked by the GABAA, agonists isoguvacine and 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and was not antagonized by the GABAA antagonist bicuculline. The putative GABAB antagonist 5-aminovaleric acid (1 mM) significantly reduced the effect of (-)-baclofen. The ability of (-)-baclofen to enhance VIP-stimulated accumulation of cyclic AMP was observed in slices of rat cerebral cortex, hippocampus, and hypothalamus. These results indicate that GABA and (-)-baclofen can enhance VIP-stimulated accumulation of cyclic AMP in rat brain slices via an interaction with specific GABAB receptors.