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PubMed2002

Consequences of altered TGF-beta expression and responsiveness in breast cancer: evidence for autocrine and paracrine effects.

To characterize the impact of increased production of TGF-beta in a xenograft model of human breast cancer, TGF-beta-responsive MDA-231 cells were genetically modified by stable transfection so as to increase their production of active TGF-beta1. Compared with control cells, cells that produced increased amounts of TGF-beta proliferated in vitro more slowly. In vivo, however, tumors derived from these cells exhibited increased proliferation and grew at an accelerated pace. To evaluate the role of autocrine TGF-beta signaling, cells were also transfected with a dominant-negative truncated type II TGF-beta receptor (TbetaRII). Disruption of autocrine TGF-beta signaling in the TGF-beta-overexpressing cells reduced their in vivo growth rate. Co-inoculation of Matrigel with the TGF-beta-overexpressing cells expressing the truncated TbetaRII compensated for their diminished in vivo growth capacity, compared with the TGF-beta-overexpressing cells with an intact autocrine loop. Tissue invasion by the tumor was a distinctive feature of the TGF-beta-overexpressing cells, whether or not the autocrine loop was intact. Furthermore, tumors derived from TGF-beta-overexpressing cells, irrespective of the status of the autocrine TGF-beta-signaling pathway, had a higher incidence of lung metastasis. Consistent with the suggestion that TGF-beta's enhancement of invasion and metastasis is paracrine-based, we observed no significant differences among the cell clones in an in vitro invasion assay. Thus, in this experimental model system in vitro assays of cell proliferation and invasion do not accurately reflect in vivo observations, perhaps due to autocrine and paracrine effects of TGF-beta that influence the important in vivo-based phenomena of tumor growth, invasion, and metastasis.

Animals↗
PubMed2002

Paracrine cyclooxygenase-2-mediated signalling by macrophages promotes tumorigenic progression of intestinal epithelial cells.

In human colorectal adenomas or polyps, cyclooxygenase-2 is expressed predominantly by stromal (or interstitial) macrophages. Therefore, we tested the hypothesis that macrophage cyclooxygenase-2 has paracrine pro-tumorigenic activity using in vitro models of macrophage-epithelial cell interactions. We report that macrophages can promote tumorigenic progression of intestinal epithelial cells (evidenced by decreased cell-cell contact inhibition, increased proliferation and apoptosis, gain of anchorage-independent growth capability, decreased membranous E-cadherin expression, up-regulation of cyclooxygenase-2 expression, down-regulation of transforming growth factor-beta type II receptor expression and resistance to the anti-proliferative activity of transforming growth factor-beta(1)) in a paracrine, cyclooxygenase-2-dependent manner. Pharmacologically relevant concentrations (1-2 microM) of a selective cyclooxygenase-2 inhibitor had no detectable, direct effect on intestinal epithelial cells but inhibited the macrophage-epithelial cell signal mediating tumorigenic progression. Cyclooxygenase-2-mediated stromal-epithelial cell signalling during the early stages of intestinal tumorigenesis provides a novel target for chemoprevention of colorectal cancer (and other gastro-intestinal epithelial malignancies, which arise on a background of chronic inflammation, such as gastric cancer) and may explain the discrepancy between the concentrations of cyclooxygenase inhibitors required to produce anti-neoplastic effects in vitro and in vivo.

Animals↗
PubMed1999

'Paracrine' control of spermatogenesis.

Spermatogenesis is a remarkably complex but precise process yielding highly differentiated haploid germ cells from diploid stem cells. Although many factors have been implicated in the paracrine control of spermatogenesis, functional proof is only available for a few regulators. Among those are androgens, growth factors and stem cell factor. Cell- and organ-specific genetargeting will provide important insights into the relevance of local factors controlling male gametogenesis. As testicular communication frequently occurs between rather remote cells and compartments, it is proposed that the term 'local' rather than 'paracrine' mediators/factors should be used, since the latter term refers to communication amongst neighbouring cells (and mainly via diffusion).

Animals↗
PubMed2001

Sites of epidermal growth factor synthesis and action in the pituitary: paracrine and autocrine interactions.

1. Epidermal growth factor (EGF) is produced by growth hormone (GH) cells and gonadotropes in normal pituitary cell populations. The studies were initiated to determine whether EGF is a paracrine or autocrine regulator of gonadotrope function. 2. The first group of studies tested for the presence of EGF receptors in gonadotropes from cycling female rats by immunolabelling. Expression varied with the stage of the cycle. At the highest point (metoestrus), only a few EGF target cells are gonadotropes, identified by their content of luteinizing hormone (LH)-beta mRNA. Expression by gonadotropes then increased to reach a peak of 50% of cells during pro-oestrus. 3. Studies investigating the regulation of expression of EGF receptor (R) showed that all culture conditions (in media with or without serum) and EGF itself both stimulated expression of the receptor by gonadotropes in populations from oestrus or metoestrus rats. Gonadotropin-releasing hormone (GnRH) also stimulated EGFR expression in follicle-stimulating hormone (FSH) gonadotropes from oestrus animals. Additional tests of expression of immediate early genes (c-fos) showed that, after 15 min, EGF stimulated expression in cells with FSH antigens. 4. Epidermal growth factor also stimulated gonadotrope proliferation, as detected by the MTT cell growth/cell death assays and bromodeoxyuridine uptake by gonadotropes during the S phase (DNA synthesis) of the cell cycle. 5. Epidermal growth factor and GnRH both stimulated a significant increase in the percentage of mitotic gonadotropes. Epidermal growth factor may be an autocrine or a paracrine growth factor to maintain and develop the gonadotrope population and EGF may also be involved in early differentiation events that prepare cells to support the LH surge.

Animals↗
PubMed2002

Adrenocortical peptides: autocrine or paracrine regulators for the steroid hormone secretion or the cell proliferation?

There is accumulating evidence that indicates the production and secretion of some peptides by adrenal cortex and adrenocortical tumors. These peptides include adrenomedullin, proadrenomedullin N-terminal 20 peptide (PAMP), endothelin-1, cerebellin, urotensin-II etc., and appear to be involved in the regulation of steroid hormone secretion and the proliferation of adrenocortical cells as autocrine and/or paracrine factors. It is noteworthy that expression of adrenomedullin is induced by hypoxia and inflammatory cytokines in various cells, raising the possibility that the adrenocortical production of adrenomedullin (and probably PAMP) may be increased in some inflammatory and/or ischemic conditions, and these two peptides may modulate the states of inflammatory and/or ischemic disorders. In addition to adrenomedullin and PAMP, adrenal cortex and/or some adrenocortical tumors express endothelin-1, cerebellin, urotensin-II, etc. The adrenocortical peptides may form a novel autocrine or paracrine regulatory system for the steroid hormone secretion and the cell proliferation in the adrenal cortex, and involve in the pathophysiology of inflammatory, ischemic or neoplastic diseases of the adrenal cortex

Adrenal Cortex↗
PubMed2002

Paracrine in vivo inhibitory effects of hepatitis B virus X protein (HBx) on liver cell proliferation: an alternative mechanism of HBx-related pathogenesis.

The role of the hepatitis B virus X protein (HBx) in the pathogenesis of hepatitis B virus (HBV) infection remains unclear. HBx exhibits pleiotropic biological effects, whose in vivo relevance is a matter for debate. In the present report, we have used a combination of HBx-expressing transgenic mice and liver cell transplantation to investigate the in vivo impact of HBx expression on liver cell proliferation and viability in a regenerative context. We show that moderate HBx expression inhibits liver regeneration after partial hepatectomy in HBx-expressing transgenic mice. We also demonstrate that the transplantation of HBx-expressing liver cells, isolated from HBx transgenic mice, is sufficient to inhibit overall recipient liver regeneration after partial hepatectomy. Moreover, the injection of serum samples drawn from HBx-expressing transgenic mice mimicked the inhibitory effect of HBx on liver regeneration. Finally, the incubation of primary rat hepatocytes with the supernatant of HBx-expressing liver cells inhibits cellular DNA synthesis. Taken together, our results demonstrate a paracrine inhibitory effect of HBx on liver cell proliferation and lead us to propose HBV as one of the few viruses implicated in human cancer which act, at least in part, through paracrine biological pathways.

Animals↗
PubMed1998

In vivo evidence that the stromelysin-3 metalloproteinase contributes in a paracrine manner to epithelial cell malignancy.

Stromelysin-3 (ST3; Basset, P., J.P. Bellocq, C. Wolf, I. Stoll, P. Hutin, J.M. Limacher, O.L. Podhajcer, M.P. Chenard, M.C. Rio, P. Chambon. 1990. Nature. 348:699-704) is a matrix metalloproteinase (MMP) expressed in mesenchymal cells located close to epithelial cells, during physiological and pathological tissue remodeling processes. In human carcinomas, high ST3 levels are associated with a poor clinical outcome, suggesting that ST3 plays a role during malignant processes. In this study we report the ST3 gene inactivation by homologous recombination. Although ST3 null mice (ST3-/-) were fertile and did not exhibit obvious alterations in appearance and behavior, the lack of ST3 altered malignant processes. Thus, the suppression of ST3 results in a decreased 7, 12-dimethylbenzanthracene-induced tumorigenesis in ST3-/- mice. Moreover, ST3-/- fibroblasts have lost the capacity to promote implantation of MCF7 human malignant epithelial cells in nude mice (P < 0.008). Finally, we show that this ST3 paracrine function requires extracellular matrix (ECM)-associated growth factors. Altogether, these findings give evidence that ST3 promotes, in a paracrine manner, homing of malignant epithelial cells, a key process for both primary tumors and metastases. Therefore, ST3 represents an appropriate target for specific MMP inhibitor(s) in future therapeutical approaches directed against the stromal compartment of human carcinomas.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2006

Paracrine release of insulin-like growth factor 1 from a bioengineered tissue stimulates skeletal muscle growth in vitro.

Bioengineered tissues transduced to secrete recombinant proteins may serve as a long-term delivery vehicle for therapeutic proteins when implanted in vivo. Insulin-like growth factor 1 (IGF1) is an anabolic growth factor for skeletal muscle that can stimulate myoblast proliferation and myofiber hypertrophy. To determine whether the release of IGF1 from an engineered bioartificial skeletal muscle (BAM) could stimulate the growth of skeletal muscle in a paracrine manner, we established an in vitro perfusion system for genetically engineered IGF1 BAMs. BAMs were bioengineered from C2C12 murine myoblasts stably transduced with a retroviral vector to synthesize and secrete IGF1 (C2-IGF1 BAMs). C2-IGF1 BAMs or nontransduced control C2 BAMs were cocultured with avian BAMS (ABAMs) in constantly perfused biochambers. During 11 days of perfusion, IGF1 levels in the C2-IGF1 BAM perfusion medium increased linearly from 1 to 20 ng/mL. The ABAMs maintained in biochambers with the C2-IGF1 BAMs had significantly more myofibers (69%, p < 0.005) and larger myofiber cross-sectional areas (40%, p < 0.001) compared to those cocultured with control C2 BAMs. These studies show that levels of IGF1 secreted from the C2-IGF1 BAMs are sufficient to produce an anabolic paracrine effect on nongenetically engineered BAMs, and the in vitro perfusion system provides a model for screening proteins effective in stimulating localized skeletal muscle growth.

Animals↗
PubMed2006

Decidual stromal cell response to paracrine signals from the trophoblast: amplification of immune and angiogenic modulators.

During the invasive phase of implantation, trophoblasts and maternal decidual stromal cells secrete products that regulate trophoblast differentiation and migration into the maternal endometrium. Paracrine interactions between the extravillous trophoblast and the maternal decidua are important for successful embryonic implantation, including establishing the placental vasculature, anchoring the placenta to the uterine wall, and promoting the immunoacceptance of the fetal allograph. To our knowledge, global crosstalk between the trophoblast and the decidua has not been elucidated to date, and the present study used a functional genomics approach to investigate these paracrine interactions. Human endometrial stromal cells were decidualized with progesterone and further treated with conditioned media from human trophoblasts (TCM) or, as a control, with control conditioned media (CCM) from nondecidualized stromal cells for 0, 3, and 12 h. Total RNA was isolated and processed for analysis on whole-genome, high-density oligonucleotide arrays containing 54,600 genes. We found that 1374 genes were significantly upregulated and that 3443 genes were significantly downregulated after 12 h of coincubation of stromal cells with TCM, compared to CCM. Among the most upregulated genes were the chemokines CXCL1 (GRO1) and IL8,CXCR4, and other genes involved in the immune response (CCL8 [SCYA8], pentraxin 3 (PTX3), IL6, and interferon-regulated and -related genes) as well as TNFAIP6 (tumor necrosis factor alpha-induced protein 6) and metalloproteinases (MMP1, MMP10, and MMP14). Among the downregulated genes were growth factors, e.g., IGF1, FGF1, TGFB1, and angiopoietin-1, and genes involved in Wnt signaling (WNT4 and FZD). Real-time RT-PCR and ELISAs, as well as immunohistochemical analysis of human placental bed specimens, confirmed these data for representative genes of both up- and downregulated groups. The data demonstrate a significant induction of proinflammatory cytokines and chemokines, as well as angiogenic/static factors in decidualized endometrial stromal cells in response to trophoblast-secreted products. The data suggest that the trophoblast acts to alter the local immune environment of the decidua to facilitate the process of implantation and ensure an enriched cytokine/chemokine environment while limiting the mitotic activity of the stromal cells during the invasive phase of implantation.

Angiogenic Proteins↗
PubMed1997

Paracrine regulation of colony-stimulating factor-1 in medulloblastoma: implications for pathogenesis and therapeutic interventions.

OBJECTIVE: Colony-stimulating factor (CSF)-1, a chemotactic and mitogenic factor for macrophages and microglia, is expressed in a variety of nervous system tumors and when present in nonneural malignancies, is associated with marked inflammatory infiltrates, dissemination, and poorer prognosis. This study investigated the paracrine effects of CSF-1 production by medulloblastoma cells on the macrophage/microglial lineage. METHODS: A recurrent metastatic desmoplastic medulloblastoma was isolated from a 26-year-old man and propagated in tissue culture. Cellular phenotype and proliferation were assessed by immunocytochemical techniques; transcript expression for CSF-1, granulocyte macrophage-CSF, interleukin-3, and c-fms (the receptor for CSF-1) was examined with reverse transcriptase-polymerase chain reaction; and conditioned media and coculture paradigms were used to study cytokine effects on cellular proliferation. RESULTS: Serially passaged cells were uniformly immunoreactive for two lineage-independent neuroepithelial markers, nestin and vimentin. A subpopulation of cells with morphological characteristics of early differentiation stained for neurofilament 66 (7%) and microtubule-associated protein (5%) (markers of early neuronal precursors and postmitotic neurons, respectively) and for the Yp subunit of glutathione-S-transferase (3%) (a marker of early oligodendroglial progenitors). Tumor cells expressed transcripts for CSF-1, but not for granulocyte macrophage-CSF, interleukin-3, or c-fms. Treatment of microglia with serum-free medulloblastoma-conditioned media significantly increased proliferation (P < 0.001), suggesting the secretion of CSF-1. Coculture of medulloblastoma cells and microglia significantly increased proliferation of both cell types (each condition, P < 0.01). CONCLUSION: These observations suggest that CSF-1 mediates important paracrine interactions between transformed cells and the immune system, resulting in increased growth rate and metastatic potential. Future therapeutic goals need to include immunotherapeutic protocols to modulate this interaction.

Adult↗
PubMed1999

Paracrine upregulation of VEGF receptor mRNA in endothelial cells by hypoxia-exposed hep G2 cells.

Although vascular endothelial growth factor (VEGF) plays a role in the growth of hypervascular tumors, mechanisms for paracrine regulation of its receptor expression on vascular endothelial cells remain unknown. This study aimed to investigate whether VEGF released from hypoxia-exposed Hep G2 cells alters expression of the two distinct receptors, kinase insert domain-containing receptor (KDR) and fms-like tyrosine kinase 1 (flt-1), in human umbilical venous endothelial cells (HUVEC). Hep G2 cells were cultured in 20% or 1% O2 for 16 h to examine induction of VEGF mRNA and its protein expression. Conditioned medium from Hep G2 cells (CM) was applied to HUVEC under normoxic conditions, and expression of mRNA for the VEGF receptors was determined by RT-PCR. In response to the hypoxic challenge, Hep G2 cells upregulated VEGF mRNA and the release of VEGF. Hypoxia-CM preferentially stimulated the mRNA expression of flt-1 but not that of KDR in HUVEC. When the VEGF release from hypoxia-exposed Hep G2 cells was blocked by its antisense oligodeoxynucleotide, the endothelial flt-1 mRNA upregulation elicited by the hypoxia-CM was still maintained. These results suggest that hypoxia-exposed Hep G2 cells not only produce VEGF but also evolve paracrine induction of flt-1 through VEGF-independent mechanisms.

Carcinoma, Hepatocellular↗
PubMed2001

Intestinal serotonin acts as paracrine substance to mediate pancreatic secretion stimulated by luminal factors.

We recently demonstrated that luminal factors such as osmolality, disaccharides, and mechanical stimulation evoke pancreatic secretion by activating 5-hydroxytryptamine subtype 3 (serotonin-3, 5-HT3) receptors on mucosal vagal afferent fibers in the intestine. We hypothesized that 5-HT released by luminal stimuli acts as a paracrine substance, activating the mucosal vagal afferent fibers to stimulate pancreatic secretion. In the in vivo rat model, luminal perfusion of maltose or hypertonic NaCl increased 5-HT level threefold in intestinal effluent perfusates. Similar levels were observed after intraluminal 10(-5) M 5-HT perfusion. These treatments did not affect 5-HT blood levels. In a separate study, intraduodenal, but not intraileal, 5-HT application induced a dose-dependent increase in pancreatic protein secretion, which was not blocked by the CCK-A antagonist CR-1409. Acute vagotomy, methscopolamine, or perivagal or intestinal mucosal application of capsaicin abolished 5-HT-induced pancreatic secretion. In conscious rats, luminal 10(-5) M 5-HT administration produced a 90% increase in pancreatic protein output, which was markedly inhibited by the 5-HT3 antagonist ondansetron. In conclusion, luminal stimuli induce 5-HT release, which in turn activates 5-HT3 receptors on mucosal vagal afferent terminals. In this manner, 5-HT acts as a paracrine substance to stimulate pancreatic secretion via a vagal cholinergic pathway.

Animals↗
PubMed2004

Human neutrophils promote angiogenesis by a paracrine feedforward mechanism involving endothelial interleukin-8.

Neovascularization by sprouting angiogenesis is critical for inflammation-mediated tissue remodeling and wound healing. We report here that human polymorphonuclear neutrophils (PMN) stimulated for 1 h with 100 nM N-formyl-methionyl-leucyl-phenylalanine (fMLP) released a proangiogenic entity that induced sprouting of capillary-like structures in an in vitro angiogenesis assay. The effect was comparable to the response obtained on stimulation with 100 ng/ml basic FGF. The PMN-mediated response was inhibited by neutralizing antibodies against VEGF or IL-8. As measured by ELISA technique, we found that fMLP-activated PMN (5 x 10(6)/ml) released 78 pg/ml IL-8 and 39 pg/ml VEGF within 1 h after stimulation. IL-8 release was blocked by actinomycin D or cycloheximide, but the inhibitors had no effect on VEGF release, suggesting that IL-8 secretion required de novo synthesis whereas VEGF was secreted from preformed stores. Accordingly, RT-PCR analysis revealed that IL-8 mRNA was upregulated on PMN stimulation, whereas the expression of VEGF mRNA was not affected. Moreover, supernatant derived from activated PMN induced upregulation of endothelial IL-8 mRNA expression, suggesting that release of VEGF and IL-8 from activated PMN may activate a paracrine feedforward mechanism involving endothelial IL-8. Moreover, VEGF-induced upregulation of endothelial IL-8 expression as well as sprouting of capillary-like structures was inhibited by a neutralizing anti-IL-8 antibody. These findings suggest that bacteria-derived tripeptides stimulate human PMN to release VEGF and IL-8, which activate endothelial cells and induce angiogenesis by a paracrine feedforward mechanism involving endothelial IL-8 upregulation.

Cells, Cultured↗
PubMed2005

Paracrine mitogenic effect of human endothelial progenitor cells: role of interleukin-8.

Endothelial progenitor cells (EPCs) play an important role in repair of vascular injury and neovascularization. Molecular mechanisms underlying vascular effects of EPCs are not fully understood. The present study was designed to test the hypothesis that human EPCs exert a strong paracrine mitogenic effect on mature endothelial cells. Levels of interleukin-8 (IL-8) were significantly higher in conditioned medium (CM) collected from EPCs than in CM derived from mature endothelial cells [umbilical vein endothelial cells (HUVECs) and coronary artery endothelial cells (CAECs)]. CM of EPCs stimulated proliferation of HUVECs and CAECs. This mitogenic effect was partially inhibited by IL-8-neutralizing antibody. In contrast, CM of HUVECs and CAECs had a weak or no mitogenic effect on mature endothelial cells. Our results demonstrate significantly higher levels of IL-8 secretion by human EPCs than by mature endothelial cells. IL-8 appears to be an important mediator of the paracrine mitogenic effect of EPCs.

Adult↗
PubMed2002

Stretch-stimulated surfactant synthesis is coordinated by the paracrine actions of PTHrP and leptin.

Intrauterine lung development, culminating in physiological pulmonary surfactant production by epithelial type II (TII) cells, is driven by fluid distension through unknown mechanisms. Differentiation of alveolar epithelial and mesenchymal cells is mediated by soluble factors like parathyroid hormone-related protein (PTHrP), a stretch-sensitive TII cell product. PTHrP stimulates pulmonary surfactant production by a paracrine feedback loop mediated by leptin, a soluble product of the mature lipofibroblast (LF). When LFs and TIIs are stretched in coculture, there is a fivefold increase in surfactant phospholipid synthesis that can be "neutralized" by inhibitors of PTHrP or leptin, implicating a paracrine feedback loop in this mechanism. Stretching LFs stimulates PTHrP binding (2.5-fold) and downstream stimulation of triglyceride uptake quantitatively (15-25%) due to upregulation of adipose differentiation-related protein expression. Stretching TII cells increases leptin stimulation of their surfactant phospholipid synthesis threefold, suggesting that retrograde signaling by leptin to TII cells is also stretch sensitive. We conclude that the effect of stretch on alveolar LF and TII differentiation is coordinated by PTHrP, leptin, and their receptors.

Animals↗
PubMed2007

Vasculotropic, paracrine actions of infused mesenchymal stem cells are important to the recovery from acute kidney injury.

Acute kidney injury (AKI) is a major clinical problem in which a critical vascular, pathophysiological component is recognized. We demonstrated previously that mesenchymal stem cells (MSC), unlike fibroblasts, are significantly renoprotective after ischemia-reperfusion injury and concluded that this renoprotection is mediated primarily by paracrine mechanisms. In this study, we investigated whether MSC possess vasculoprotective activity that may contribute, at least in part, to an improved outcome after ischemia-reperfusion AKI. MSC-conditioned medium contains VEGF, HGF, and IGF-1 and augments aortic endothelial cell (EC) growth and survival, a response not observed with fibroblast-conditioned medium. MSC and EC share vasculotropic gene expression profiles, as both form capillary tubes in vitro on Matrigel alone or in cooperation without fusion. MSC undergo differentiation into an endothelial-like cell phenotype in culture and develop into vascular structures in vivo. Infused MSC were readily detected in the kidney early after reflow but were only rarely engrafted at 1 wk post-AKI. MSC attached in the renal microvascular circulation significantly decreased apoptosis of adjacent cells. Infusion of MSC immediately after reflow in severe ischemia-reperfusion AKI did not improve renal blood flow, renovascular resistance, or outer cortical blood flow. These data demonstrate that the unique vasculotropic, paracrine actions elicited by MSC play a significant renoprotective role after AKI, further demonstrating that cell therapy has promise as a novel intervention in AKI.

Acute Disease↗
PubMedDate not supplied

Fetal-placental and decidual-placental units: role of endocrine and paracrine regulations in parturition.

In primates, fetal adrenal and placental steroidogenic enzymatic systems are complementary in a fetal-placental unit, synchronizing fetal maturation and myometrial activation in late gestation. Moreover, as hemochorial placentation characterizes rodents and primates, paracrine regulations between decidua and placenta are essential to the immunotolerance of the conceptus and its development. Thus, the decidual-placental unit remains in a striking state of decidual quiescence throughout gestation, and the reversal of this quiescence is thought to play a key role in myometrial stimulation and the onset of parturition. A comprehensive view of the control of myometrial contractility, through the interaction of paracrine and endocrine modifications in late gestation, is proposed. The failure of these mechanisms underlie prematurity and the use of fetal therapy in threatened preterm labor.

Animals↗
PubMed1998

Direct action of serotonin on prolactin, growth hormone, corticotropin and luteinizing hormone release in cocultures of anterior and posterior pituitary lobes: autocrine and/or paracrine action of vasoactive intestinal peptide.

There is extensive evidence that serotonin (5-HT) is implicated in the neuroendocrine control regulating the secretion of several anterior pituitary hormones. It has also been reported that the posterior pituitary is necessary for prolactin (PRL) response to 5-HT as well as to suckling, in which 5-HT implication has been demonstrated. As we have previously shown that vasoactive intestinal peptide (VIP) mediates through an autocrine or paracrine action the PRL release induced by insulin-like growth factor I, thyrotropin-releasing hormone (TRH) and dopamine withdrawal, the aim of the present work was to determine whether 5-HT has a direct action on pituitary secretion and to study the possible role of pituitary VIP in this situation. Cells from the anterior pituitary lobe (AP) were cultured either alone or together with cells from the posterior pituitary lobe (PP). As melanotropes from PP express glucocorticoid receptors in vitro, both AP cultures and cocultures of AP/PP cells were incubated in the presence or absence of corticosterone (0.1 microg/ml), thus designing four experimental conditions. Then both AP and mixed cultures were incubated with 5-HT (100 nM) for 20, 45 and 180. The release of PRL, growth hormone (GH), corticotropin (ACTH) and luteinizing hormone (LH) was stimulated by 5-HT, but only in cocultures of AP/PP cells preincubated with corticosterone, whereas follicle-stimulating hormone and thyroid-stimulating hormone release was not modified. As AP cultures did not show any response to 5-HT, both in the presence or absence of corticosterone, and as melanotropes are the main cellular type present in the PP cultures, we studied the response of alpha-melanocyte-stimulating hormone (alphaMSH) to 5-HT in PP cells cultured with or without corticosterone. Serotonin did not modify alphaMSH release either in the absence or the presence of corticosterone. VIP release was also stimulated by 5-HT in the cocultures, and the time response profile was only similar to that of PRL. In order to study whether pituitary VIP is implicated in 5-HT action, cocultures preincubated with corticosterone were incubated in the presence of 5-HT, a VIP-receptor antagonist (VIP-At) or simultaneously with 5-HT plus VIP-At. PRL response to 5-HT was abolished by the simultaneous presence of VIP-At, whereas GH, ACTH and LH response remained unchanged. These data demostrate that: (1) 5-HT stimulates the secretion of PRL, GH, ACTH, LH and VIP acting directly at pituitary level on PP, probably by releasing an unidentified mediator from melanotropes; (2) glucocorticoids make the response of AP cells to 5-HT possible due to the presence of PP cells in the coculture; (3) PRL response to 5-HT is mediated through an autocrine and/or paracrine action of VIP.

Adrenocorticotropic Hormone↗