Mechanism of VIPR1 gene regulating human lung adenocarcinoma H1299 cells.

The vasoactive intestinal peptide receptor-1(VIPR1) has prominent growth effects on a number of common neoplasms. However, there were contradictions in the effect cross different cancers. We aimed to explore the effect of VIPR1 overexpression on a human lung adenocarcinoma cell line H1299. GEO dataset was used to screen differentially expressed genes in lung adenocarcinoma tissues. The expression of VIPR1 mRNA was determined in the cancer Genome Atlas (TCGA). Immunohistochemical analysis was performed to determine VIPR1 protein expression in lung adenocarcinoma and corresponding adjacent tissues (n = 22). Fluorescence real-time quantitative PCR detected the expression of VIPR1 in human normal lung epithelial cell line BEAS-2B and lung adenocarcinoma cell line H1299. Overexpression strategies were employed to assess functions of VIPR1 expression on several malignant phenotypes in H1299. The expression of VIPR1 was lower in lung adenocarcinoma tissues than that in adjacent tissues. Compared with the normal lung epithelial cells BEAS-2B, VIPR1 was down-regulated in lung cancer cells H1299 (P < 0.05). After the overexpression of VIPR1, we found that VIPR1 significantly inhibited growth, migration, and invasion of H1299 cells (P < 0.05). Our findings point out the tumor suppressor roles of VIPR1 in human LUAD pathogenesis.

Upregulation of intestinal mucosal mast cells expressing VPAC1 in close proximity to vasoactive intestinal polypeptide in inflammatory bowel disease and murine colitis.

BACKGROUND: Mast cells (MCs) and vasoactive intestinal polypeptide (VIP) have been proposed as regulators of the intestinal barrier and inflammation. Our aim was to map the distribution in inflammatory bowel disease (IBD) and murine colitis. METHODS: MCs, VIP, and VIP-receptors (VPACs) were quantified by immunofluorescence and enzyme-immunoassay (EIA) in ileal tissues (villus epithelium (VE) and adjacent VE, ie, VE next to the follicle-associated epithelium, (FAE)) from Crohn's disease (CD; n = 16) and non-IBD patients, and in colonic specimens of ulcerative colitis (UC; n = 12) and healthy controls (HCs). In addition, VIP levels were measured in plasma from HCs, non-IBD, and IBD in remission (CD n = 30; UC n = 30). Colon, ileum, and plasma from mice with dextran sulfate sodium (DSS)-induced colitis and control mice were analyzed likewise. KEY RESULTS: FAE-adjacent VE in ileum of CD possessed more MCs (P < 0.05) and MCs expressing VPAC1 (P < 0.05), but not VPAC2, compared to controls. Both adjacent and regular VE of CD had more MCs co-localizing/in close proximity to VIP (P < 0.05). In UC colon, more MCs (P < 0.0005), MCs close to VIP (P < 0.0005), and MCs expressing VPAC1 (P < 0.05) were found compared to controls. VIP levels were elevated in plasma from CD and UC compared to controls (P < 0.0005). Colon of DSS mice showed more MCs and MCs close to VIP (P < 0.05) compared to control mice. In vitro experiments revealed MCs expressing VPACs and internalized VIP after 120 minutes of VIP-stimulation. CONCLUSIONS AND INFERENCES: Communication between MCs and VIP is upregulated during IBD and mice colitis. In CD patients, the epithelium next to FAE seems to be more involved than the surrounding VE, suggesting increased MC-VIP-interactions in this intestinal region.

Neuroleptic Drugs and PACAP Differentially Affect the mRNA Expression of Genes Encoding PAC1/VPAC Type Receptors.

Several lines of evidence suggest that pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide playing an important role as a neuromodulator. It has been indicated that PACAP is associated with mental diseases, and that regulation of the PACAPergic signals could be a potential target for the treatment of such psychiatric states as schizophrenia. Recent studies have suggested that action of neuroleptic drugs is mediated not only by dopaminergic and serotonergic neurotransmission, but also via neuropeptides which may act both as neurotransmitters and as neuromodulators. The present study examines whether currently-used neuroleptics influence the action of PACAP receptors, whose expression is altered in a schizophrenic patient. Real-time polymerase chain reaction (PCR) was used to examine the effects of haloperidol, olanzapine and amisulpride on the expression of genes coding PAC1/VPAC type receptors in the T98G glioblastoma cell line, as an example of an in vitro model of glial cells. PAC1 mRNA expression fell after 24-h incubation with haloperidol or olanzapine; however the effect was not maintained after 72 h, and haloperidol even up-regulated PAC1 mRNA expression in a dose-dependent manner. All the examined drugs decreased VPAC2 mRNA expression, especially after 72-h incubation. Haloperidol (typical neuroleptic) was distinctly more potent than atypical neuroleptic drugs (olanzapine and amisulpride). In addition, PACAP increased PAC1 and VPAC2 mRNA expression. In conclusion, our findings suggest PACAP receptors may be involved in the mechanism of typical and atypical neuroleptic drugs.

VIP impairs acquisition of the macrophage proinflammatory polarization profile.

This study tested the hypothesis that vasoactive intestinal peptide (VIP) is able to modify the macrophage inflammatory profile, thus supporting its therapeutic role in autoimmune diseases. Macrophages are innate immune cells that display a variety of functions and inflammatory profiles in response to the environment that critically controls their polarization. Deregulation between the pro- and anti-inflammatory phenotypes has been involved in different pathologies. Rheumatoid arthritis (RA) is an autoimmune disease, in which macrophages are considered central effectors of synovial inflammation, displaying a proinflammatory profile. VIP is a pleiotropic neuropeptide with proven anti-inflammatory actions. As modulation of the macrophage phenotype has been implicated in the resolution of inflammatory diseases, we evaluated whether VIP is able to modulate human macrophage polarization. In vitro-polarized macrophages by GM-CSF (GM-MØ), with a proinflammatory profile, expressed higher levels of VIP receptors, vasoactive intestinal polypeptide receptors 1 and 2 (VPAC1 and VPAC2, respectively), than macrophages polarized by M-CSF (M-MØ) with anti-inflammatory activities. RA synovial macrophages, according to their GM-CSF-like polarization state, expressed both VPAC1 and VPAC2. In vitro-generated GM-MØ exposed to VIP exhibited an up-regulation of M-MØ gene marker expression, whereas their proinflammatory cytokine profile was reduced in favor of an anti-inflammatory function. Likewise, in GM-MØ, generated in the presence of VIP, VIP somehow changes the macrophages physiology profile to a less-damaging phenotype. Therefore, these results add new value to VIP as an immunomodulatory agent on inflammatory diseases.

VPAC1 Targeted (64)Cu-TP3805 Positron Emission Tomography Imaging of Prostate Cancer: Preliminary Evaluation in Man.

OBJECTIVE: To evaluate (64)Cu-TP3805 as a novel biomolecule, to positron emission tomography (PET) image prostate cancer (PC), at the onset of which VPAC1, the superfamily of G protein-coupled receptors, is expressed in high density on PC cells, but not on normal cells. MATERIALS AND METHODS: Twenty-five patients undergoing radical prostatectomy were PET/X-ray computerized tomography imaged preoperatively with (64)Cu-TP3805. Standardized maximum uptake (SUVmax) values were determined and malignant lesions (standardized uptake value > 1.0) counted, and compared with histologic findings. Whole-mount pathology slides from 6 VPAC1 PET imaged patients, 3 benign prostatic hyperplasia patients, 1 malignant and 1 benign lymph node underwent digital autoradiography (DAR) after (64)Cu-TP3805 incubation and were compared to hematoxylin- and eosin-stained slides. RESULTS: In 25 patients who underwent PET imaging, 212 prostate gland lesions had SUVmax > 1.0 vs 127 lesions identified by histology of biopsy tissues. The status of the additional 85 PET identified prostate lesions remains to be determined. In 68 histologic slides from 6 PET imaged patients, DAR identified 105 of 107 PC foci, 19 of 19 high-grade prostatic intraepithelial neoplasias, and ejaculatory ducts and verumontanum involved with cancer. Additionally, DAR found 9 PC lesions not previously identified histologically. The positive and negative lymph nodes were correctly identified, and in 3 of 3 benign prostatic hyperplasia patients and 5 of 5 cysts, DAR was negative. CONCLUSION: This feasibility study demonstrated that (64)Cu-TP3805 delineates PC in vivo and ex vivo, provided normal images for benign masses, and is worthy of further studies.

VPAC1 overexpression is associated with poor differentiation in colon cancer.

Vasoactive intestinal peptide (VIP) is a neurotransmitter that primarily functions as a vasodilator. VIP plays its role through binding to its receptors known as VIP/pituitary adenylate cyclase-activating peptide receptors (VPACs). In this study, we examined the expression of VPAC1 in human colon cancer tissues, analyzed the relationship between VPAC1 expression and cancer malignancy, and explored the possible mechanisms using immunohistochemistry and immunofluorescence double staining. The results showed that (1) poorly differentiated colon cancers have significantly higher VPAC1 expression than well-differentiated colon cancers do (p < 0.01); (2) phospho-epithelial growth factor receptor (EGFR) overexpression/activation in the cytoplasm of cancer cells is related to VPAC1 overexpression; (3) blood vessels surrounding colon cancer have significantly more VPAC1-positive than normal colon mucosa does; (4) tumor-associated macrophages (TAMs) of colon cancer have a higher level of VPAC1 expression than macrophages in normal colon mucosa do. These data suggest that VPAC1 overexpression is associated with poorer differentiation of colon cancer, which is likely caused by subsequent EGFR activation in cancer cells. In addition, VPAC1 overexpression in both blood vessels and macrophages in tumors may also play an important role in the development of aggressive cancer.

Development-related splicing regulates pituitary adenylate cyclase-activating polypeptide (PACAP) receptors in the retina.

PURPOSE: The ubiquitous pituitary adenylate cyclase-activating peptide (PACAP) has a disparate array of functions in development (e.g., proliferation and apoptosis). Among three types of PACAP receptor (VPAC1, VPAC2, and PAC1), PAC1 is subject to alternative splicing that generates isoforms. Although the literature documenting the presence of PACAP receptors in the central nervous system is vast, their expression during development has not been established yet. Here, we performed quantitative analyses on the expression of PACAP receptors during the postnatal development of the rat retina. METHODS: Retinas were harvested from postnatal days 0 to 20 (P0-P20). Using a comprehensive primer system, expression changes were followed employing quantitative real-time PCR. Changes at the protein level were detected by immunoblotting using anti-VPAC1, -VPAC2, and -PAC1 receptor antibodies. RESULTS: The expression of VPAC1 showed increases at P10 and P15. Peaks in VPAC2 expression were observed at P5 and P15. Using splicing variant-specific primers for PAC1 receptor, splicing regulation of Null, Hip, Hop1, and Hiphop1 variants was revealed in correlation with postnatal development. Transcript levels of the Null and Hip variants showed a decline, while Hop1 became the major PACAP receptor by P20. Hiphop1 transcript levels did not display remarkable changes except for a transient increase at P10. Immunoblotting confirmed the presence and expression level changes of the receptors. CONCLUSIONS: We conclude that both VPAC1 and VPAC2 could have roles at all stages of retinal development, that PACAP acts through a specific set of PAC1 isoforms, and that Hip and Hop1 are predominantly involved in the postnatal development of rat retina.

Expression of VIP and its receptors in the testis of the spotted ray Torpedo marmorata (Risso 1880).

The aim of this work was to study, by immunoprecipitation, in situ hybridization and immunohistochemistry, and the expression of the vasoactive intestinal peptide (VIP) and of its receptors (VPAC(1)R and VPAC(2)R) in the testis of a nonmammalian vertebrate, the cartilaginous fish Torpedo marmorata. We demonstrated that, differently from mammals, VIP and VPAC(2)R were widely distributed in the testicular cells while the VPAC(1)R had a limited distribution. In details, we showed that VIP and VPAC(2)R were present in mitotic and differentiating germ cells as well as in the cells involved in the steroidogenesis, i.e., Leydig, Sertoli cells, and prespermatogonia and spermatogonia. The possibility that VIP is involved in the spermatogenesis and particularly in the steroidogenesis of T. marmorata is discussed.

Pituitary adenylate cyclase-activating polypeptide (PACAP) potently dilates middle meningeal arteries: implications for migraine.

Migraine is a debilitating neurological disorder characterized by mild to severe headache that is often accompanied by aura and other neurological symptoms. Among proposed mechanisms, dilation of the dural vasculature especially the middle meningeal artery (MMA) has been implicated as one component underlying this disorder. Several regulatory peptides from trigeminal sensory and sphenopalatine postganglionic parasympathetic fibers innervating these vessels have been implicated in the process including pituitary adenylate cyclase-activating polypeptide (PACAP). Although PACAP has been well described as a potent dilator in many vascular beds, the effects of PACAP on the dural vasculature are unclear. In the current study, we examined the ability of PACAP to dilate MMAs that were isolated from rats and pressurized ex vivo. PACAP38 potently dilated pressurized MMAs with an EC(50) of 1 pM. The PAC1 receptor antagonist, PACAP(6-38), abolished MMA dilation caused by picomolar concentrations of PACAP. In contrast, cerebellar arteries isolated from the brain surface were ~1,000-fold less sensitive to PACAP than MMAs. Although cerebellar arteries expressed transcripts for all three PACAP receptor subtypes (PAC1, VPAC1, and VPAC2 receptors) by RT-PCR analyses, MMA demonstrated only PAC1 and VPAC2 receptor expression. Further, multiple variants of the PAC1 receptor were identified in the MMA. The expression of PAC1 receptors and the high potency of PACAP to induce MMA vasodilation are consistent with their potential roles in the etiology of migraine.

IL-6 and PACAP receptor expression and localization after global brain ischemia in mice.

Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts a neuroprotective action against ischemic damage. This action is mediated by the interleukin-6 (IL-6) pathway. However, as the expression patterns of PACAP receptors and IL-6 following ischemia are not understood, we evaluated them in the mouse hippocampus in response to ischemia induced by bilateral common carotid artery occlusion. Real-time PCR determination of PAC1R mRNA expression in the hippocampus was significantly elevated on day 7 after ischemia. VPAC1R mRNA expression was significantly decreased 3 days after the ischemic episode, while VPAC2R mRNA expression showed a nonsignificant tendency to increase on day 7. IL-6 mRNA expression was significantly increased on day 3 and peaked on day 7 after ischemia. The mRNA expression of activity-dependent neuroprotective protein, which is a neuroprotective factor stimulated by PACAP, remained virtually unchanged in response to ischemia. IL-6 immunoreactivity was detected in the CA1 pyramidal cell layer and colocalized with the neuronal marker NeuN on day 1 after ischemia. On day 3, irregularly shaped IL-6-immunopositive cells colocalized with the astrocytic marker glial fibrillary acidic protein but not with the microglial marker Iba1. PAC1R immunoreactivity co-labeled with IL-6 immunoreactivity. These results suggest that PACAP could stimulate IL-6 secretion by neurons during the acute phase after an ischemic episode and thereafter by astrocytes during the subacute phase.

Effects of CYP-induced cystitis on PACAP/VIP and receptor expression in micturition pathways and bladder function in mice with overexpression of NGF in urothelium.

We have previously demonstrated nerve growth factor (NGF) regulation of pituitary adenylate cyclase-activating polypeptide (PACAP)/receptors in bladder reflex pathways using a transgenic mouse model of chronic NGF overexpression in the bladder using the urothelial-specific uroplakin II promoter. We have now explored the contribution of target-derived NGF in combination with cyclophosphamide (CYP)-induced cystitis to determine whether additional changes in neuropeptides/receptors are observed in micturition reflex pathways due to the presence of additional inflammatory mediators in the urinary bladder. Quantitative PCR was used to determine PACAP/vasoactive intestinal polypeptide (VIP), substance P, galanin, and receptor transcript expression in the urinary bladder (urothelium, detrusor) in mice with overexpression of NGF in the urothelium (NGF-OE) and wild-type (WT) mice with CYP-induced cystitis (4 h, 48 h, and chronic). With CYP-induced cystitis (4 h), WT and NGF-OE mice exhibited similar changes in galanin transcript expression in the urothelium (30-fold increase) and detrusor (threefold increase). In contrast, PACAP, VIP, and substance P transcripts exhibited differential changes in WT and NGF-OE with CYP-induced cystitis. PAC1, VPAC1, and VPAC2 transcript expression also exhibited differential responses in NGF-OE mice that were tissue (urothelium vs. detrusor) and CYP-induced cystitis duration-dependent. Using conscious cystometry, NGF-OE mice treated with CYP exhibited significant (p ≤ 0.01) increases in voiding frequency above that observed in control NGF-OE mice. In addition, no changes in the electrical properties of the major pelvic ganglia neurons of NGF-OE mice were detected using intracellular recording, suggesting that the urinary bladder phenotype in NGF-OE mice is not influenced by changes in the efferent limb of the micturition reflex. These studies are consistent with target-derived NGF and other inflammatory mediators affecting neurochemical plasticity and the reflex function of micturition pathways.

Gene expression of vasoactive intestinal peptide receptors in human lung cancer.

Despite significant improvement in the diagnosis and treatment of various human carcinomas, the 5-year survival rate for lung cancer remains below 20%. Vasoactive intestinal peptide (VIP) is an important neuropeptide in the control of lung physiology, and exerts its functions mainly through two receptor subtypes, VPAC1 and VPAC2. Receptors for VPAC1 and VPAC2 are present in human lung cancer cells, but very limited information exists about the mRNA expression of these VIP receptor subtypes in lung cancer specimens. The aim of the present study was to investigate by RT-PCR the mRNA expression of the VPAC1 and VPAC2 receptors in surgical specimens of 43 human lung cancer specimens and 7 normal lung samples. mRNA expression of the VPAC1 receptor was detected in 51% of the tumor specimens, while the incidence of mRNA expression for VPAC2 was 46%. Twenty-one percent of the tumor samples expressed only the VPAC1 receptor and 16% displayed only the VPAC2 receptor, while 13 samples (30%) expressed neither subtype. Thirteen cancer tissue specimens (30%), expressed both of these VIP receptor subtypes. Three normal lung tissue specimens also displayed gene expression for VPAC1 and/or VPAC2 receptors. Our results support the additional investigation of the role of VIP and its receptors in human lung cancer and suggest a further development of VIP analogs for therapeutic and imaging purposes in this malignancy.

VPAC receptor mediated tumor cell targeting by protamine based nanoparticles.

The receptors for vasoactive intestinal peptide (VIP), VPAC1-, VPAC2-, and PAC1-receptor are overexpressed by various tumor cells. VIP can target these receptors and transport conjugates into the cell. However, the use of VIP for tumor cell targeting is hampered by the peptides short half-lives due to enzymatic degradation. Because protamine-based nanoparticles (proticles) protect the peptide and serve as peptide depot, we explored the potential of proticles as carrier for VIP-conjugated molecules. The VIP-loaded proticles were stable as shown by Fluorescence Correlation Spectroscopy. With Confocal Laser Scanning Microscopy, we observed VIP-loaded proticles to specifically target the tumor cells. The cell binding triggered the substance release and conjugate internalization of VIP-Cy3 in vitro and ex vivo by human tumors. We observed VIP releasing proticle depots distributed in rat tissue and human tumors. Our findings warrant further studies to explore the proticles potential to enable peptide-mediated targeting for in vivo and clinical applications.

Imaging spontaneous MMTVneu transgenic murine mammary tumors: targeting metabolic activity versus genetic products.

UNLABELLED: Despite the great strides made in imaging breast cancer (BC) in humans, the current imaging modalities miss up to 30% of BC, do not distinguish malignant lesions from benign ones, and require histologic examinations for which invasive biopsy must be performed. Annually in the United States, approximately 5.6 million biopsies find benign lesions. More than 50% of human BCs overexpress cyclin D1, and all BCs exhibit VPAC1 oncogene products. Together, these gene products may provide an excellent biomarker for the early and accurate detection of BC. We have evaluated 4 biologically active peptide analogs that have high affinity for VPAC1. The transgenic MMTVneu mice spontaneously develop BC and metastatic lesions that overexpress cyclin D1 and VPAC1 biomarkers. The MMTVneu mouse, therefore, provides an excellent animal model that mimics the pathogenesis of human BC. The objective of this investigation was to determine the ability of 1 of the peptide analogs, (64)Cu-TP3805, to detect BC in MMTVneu mice using (18)F-FDG as a gold standard. METHODS: The transgenic MMTVneu mouse colony was maintained. Offspring were screened for transgenic status by reverse transcriptase polymerase chain reaction (RT-PCR). Nine mice with visible, palpable, or unknown metastatic lesions were entered into the protocol. (18)F-FDG (6,475 +/- 1,628 kBq [175 +/- 44 microCi]) PET served as a control, followed by a CT scan and 24-48 h later by PET with (64)Cu-TP3805 (4,588 +/- 962 kBq [124 +/- 26 microCi]). RT-PCR on excised tumors determined VPAC1 expression, and histology ascertained the pathology. RESULTS: Ten tumors were detected by PET. Four tumors were detected both by (18)F-FDG and by (64)Cu-TP3805. Additionally, 4 tumors were imaged with (64)Cu-TP3805 only. These 8 tumors overexpressed VPAC1 receptors and were malignant by histology. The 2 remaining tumors were visualized with (18)F-FDG only. These tumors did not express the VPAC1 oncogene product and had benign histology. The standard uptake value ranged from 3.1 to 18.3 for (64)Cu-TP3805 and 0.9 to 1.4 for (18)F-FDG. CONCLUSION: (64)Cu-TP3805 identified all malignant lesions unequivocally that overexpressed the VPAC1 oncogene surface product. The 2 benign tumors that did not express the VPAC1 receptor were not imaged. (64)Cu-TP3805 promises to have the potential for the early and accurate imaging of primary and metastatic BC.

PET imaging of VPAC1 expression in experimental and spontaneous prostate cancer.

UNLABELLED: Among U.S. men, prostate cancer (PC) accounts for 29% of all newly diagnosed cancers. A reliable scintigraphic agent to image PC and its metastatic or recurrent lesions and to determine the effectiveness of its treatment will contribute to the management of this disease. All PC overexpresses VPAC1 receptors. This investigation evaluated a probe specific for a (64)Cu-labeled receptor for PET imaging of experimental human PC in athymic nude mice and spontaneously grown PC in transgenic mice. METHODS: The probe, TP3939, was synthesized, purified, and labeled with (64)Cu and (99m)Tc. Using a muscle relaxivity assay, biologic activity was assessed and inhibitory concentrations of 50% calculated. Receptor affinity (Kd) for human PC3 cells was determined using (99m)Tc-TP3939 and (64)CuCl(2.) Blood clearance and in vivo stability were studied. After intravenous administration of either (64)Cu-TP3939 or (64)CuCl(2) in PC3 xenografts and in transgenic mice, PET/CT images were acquired. Prostate histology served as the gold standard. Organ distribution studies (percentage injected dose per gram [%ID/g]) in normal prostate were performed. The ratios of tumor to muscle, tumor to blood, normal prostate to muscle, and tumor to normal prostate were determined. RESULTS: Chemical and radiochemical purities of TP3939 were 96.8% and 98% +/- 2%, respectively. Inhibitory concentrations of 50% and affinity constants were 4.4 x 10(-8) M and 0.77 x 10(-9) M, respectively, for TP3939 and 9.1 x 10(-8) M and 15 x 10(-9) M, respectively, for vasoactive intestinal peptide 28. Binding of (64)CuCl(2) to PC3 was nonspecific. Blood clearance was rapid. In vivo transchelation of (64)Cu-TP3939 to plasma proteins was less than 15%. (64)Cu-TP3939 uptake in PC was 7.48 +/- 3.63 %ID/g at 4 h and 5.78 +/- 0.66 %ID/g at 24 h after injection and was significantly (P < 0.05) greater than with (64)CuCl(2) (4.79 +/- 0.34 %ID/g and 4.03 +/- 0.83 %ID/g at 4 and 24 h, respectively). The ratios of PC to normal prostate at 4 and 24 h were 4 and 2.7, respectively. (64)Cu-TP3939 distinctly imaged histologic grade IV prostate intraepithelial neoplasia in transgenic mice, but (18)F-FDG and CT did not. CONCLUSION: Data indicate that TP3939, with its uncompromised biologic activity, delineated xenografts and cases of occult PC that were not detectable with (18)F-FDG. (64)Cu-TP3939 is a promising probe for PET imaging of PC. It may also be useful for localizing recurrent lesions and for determining the effectiveness of its treatment.

Location and function of VPAC1, VPAC2 and NPR-C receptors in VIP-induced vasodilation of porcine basilar arteries.

Vasoactive intestinal peptide (VIP) is a vasodilator peptide present in cerebrovascular nerves. Vasoactive intestinal peptide can activate VPAC1, VPAC2 and the NPR-C receptor. This study sought to determine the receptors involved in VIP-induced vasodilation of porcine basilar arteries. Porcine basilar arteries contained the messenger ribonucleic acid of all three receptors. Immunocytochemical analysis of porcine basilar arteries revealed that the VPAC1 receptor is expressed on the endothelium, VPAC2 on the outer layers of the media and the NPR-C receptor throughout the artery, including nerves. Vasodilator responses to all receptor agonists showed that the receptors are functional. The vasodilator response to the VPAC1 receptor agonist was inhibited by L-NAME and abolished by endothelial denudation. Vasodilation induced by Ro-25-1553, the VPAC2 agonist, was unaffected by NOS inhibition or removal of the endothelium. Activation of the NPR-C receptor produced a vasodilation, which was susceptible to NOS inhibition and independent of endothelium. The vasodilator response to electrical stimulation at 20 Hz was attenuated by PG-99-465, the VPAC2 antagonist. This study shows that all known VIP receptors are involved in VIP-mediated vasodilation of porcine basilar arteries. The VPAC1 receptor is located on the endothelium and elicits vasodilation by generating nitric oxide (NO). The VPAC2 receptor is mainly expressed in the outer layers of the smooth muscle and induces vasodilation independently of NO in response to VIP released from intramural nerves. The NPR-C receptor produces NO-dependent vasodilation independently of the endothelium by stimulation of nNOS in intramural nerves.

Down-regulation of vasoactive intestinal peptide and altered expression of its receptors in rat diabetic cardiomyopathy.

Vasoactive intestinal peptide (VIP) is a vasorelaxant peptide that addresses two receptor subtypes, VPAC1 and VPAC2. It stimulates insulin secretion and mediates anti-inflammatory effects and has been proposed for treatment of type 2 and autoimmune diabetes. In the heart, VIP is produced and released primarily by intrinsic neurons and improves cardiac perfusion and function. Here, we investigated the involvement of this system in the events underlying development of experimentally induced diabetic cardiomyopathy. Rats received a single streptozotocin injection, and cardiac VIP content [radioimmune assay (RIA)], expression of the VIP precursors VPAC1 and VPAC2 [real-time reverse transcription-polymerase chain reaction (RT-PCR)], and VPAC1 and VPAC2 tissue distribution (immunohistochemistry) were assessed 4, 8, and 16 weeks thereafter and compared with corresponding vehicle-treated controls. Cardiac neuropathy manifests progressively during the first 4 months of diabetes at the preproVIP mRNA and VIP peptide level and is accompanied by initial down-regulation of VPAC2 at one prime target of VIP-containing axons, i.e., smooth muscle cells of coronary arterioles. VPAC1 is expressed by macrophages. After initial changes that are specific for atria and ventricles, respectively, VPAC1 and VPAC2 expression return to control levels at 16 weeks despite ongoing loss of VIP. Given the cardioprotective role of the VIP signaling system, the persistence of receptors has therapeutic implications since it is the prerequisite for trials with VPAC2 agonists.