Pituitary adenylate cyclase-activating peptide (PACAP), a new vasoactive intestinal peptide (VIP)-like peptide in the respiratory tract

Development of a New Enzyme-Linked Immunosorbent Assay (ELISA) for Measuring the Content of PACAP in Mammalian Tissue and Plasma

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a naturally occurring neuropeptide found in both the central and peripheral nervous systems of vertebrates. Recent studies have revealed the presence of PACAP and its corresponding receptors, namely, the pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1R), vasoactive intestinal peptide receptor 1 (VIPR1), and vasoactive intestinal peptide receptor 2 (VIPR2), in various structures implicated in migraine pathophysiology, including sensory trigeminal neurons. Human studies have demonstrated that when infused, PACAP can cause dilation of cranial vessels and result in delayed migraine-like attacks. In light of this, we present a novel ELISA assay that has been validated for quantifying PACAP in tissue extracts and human plasma. Using two well characterized antibodies specifically targeting PACAP, we successfully developed a sandwich ELISA assay, capable of detecting and accurately quantifying PACAP without any cross-reactivity to closely related peptides. The quantification range was between 5.2 pmol/L and 400 pmol/L. The recovery in plasma ranged from 98.2% to 100%. The increasing evidence pointing to the crucial role of PACAP in migraine pathophysiology necessitates the availability of tools capable of detecting changes in the circulatory levels of PACAP and its potential application as a reliable biomarker.

Localization of the neuropeptides pituitary adenylate cyclase-activating polypeptide, vasoactive intestinal peptide, and their receptors in the basal brain blood vessels and trigeminal ganglion of the mouse CNS; an immunohistochemical study

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are structurally related neuropeptides that are widely expressed in vertebrate tissues. The two neuropeptides are pleiotropic and have been associated with migraine pathology. Three PACAP and VIP receptors have been described: PAC1, VPAC1, and VPAC2. The localization of these receptors in relation to VIP and PACAP in migraine-relevant structures has not previously been shown in mice. In the present study, we used fluorescence immunohistochemistry, well-characterized antibodies, confocal microscopy, and three-dimensional reconstruction to visualize the distribution of PACAP, VIP, and their receptors in the basal blood vessels (circle of Willis), trigeminal ganglion, and brain stem spinal trigeminal nucleus (SP5) of the mouse CNS. We demonstrated a dense network of circularly oriented VIP fibers on the basal blood vessels. PACAP nerve fibers were fewer in numbers compared to VIP fibers and ran along the long axis of the blood vessels, colocalized with calcitonin gene-related peptide (CGRP). The nerve fibers expressing CGRP are believed to be sensorial, with neuronal somas localized in the trigeminal ganglion and PACAP was found in a subpopulation of these CGRP-neurons. Immunostaining of the receptors revealed that only the VPAC1 receptor was present in the basal blood vessels, localized on the surface cell membrane of vascular smooth muscle cells and innervated by VIP fibers. No staining was seen for the PAC1, VPAC1, or VPAC2 receptor in the trigeminal ganglion. However, distinct PAC1 immunoreactivity was found in neurons innervated by PACAP nerve terminals located in the spinal trigeminal nucleus. These findings indicate that the effect of VIP is mediated via the VPAC1 receptor in the basal arteries. The role of PACAP in cerebral arteries is less clear. The localization of PACAP in a subpopulation of CGRP-expressing neurons in the trigeminal ganglion points toward a primary sensory function although a dendritic release cannot be excluded which could stimulate the VPAC1 receptor or the PAC1 and VPAC2 receptors on immune cells in the meninges, initiating neurogenic inflammation relevant for migraine pathology.

Pituitary adenylate cyclase-activating polypeptide: Postnatal development in multiple brain stem respiratory-related nuclei in the rat

The pituitary adenylate cyclase-activating polypeptide (PACAP) plays an important role in anterior pituitary hormone secretion, neurotransmission, and the control of breathing. Mice lacking PACAP die suddenly mainly in the 2^nd postnatal week, coinciding temporally with a critical period of respiratory development uncovered by our laboratory in the rat. The goal of the current study was to test our hypothesis that PACAP expression is reduced during the critical period in normal rats. We undertook immunohistochemistry and optical densitometry of PACAP (specifically PACAP38) in several brain stem respiratory-related nuclei of postnatal days P2-21 rats, and found that PACAP immunoreactivity was significantly reduced at P12 in the pre-Bötzinger complex, nucleus ambiguus, hypoglossal nucleus, and the ventrolateral subnucleus of the nucleus tractus solitarius. No changes were observed in the control, non-respiratory cuneate nucleus at P12. Results imply that the down-regulation of PACAP during normal postnatal development may contribute to the critical period of vulnerability, when the animals' response to hypoxia is at its weakest.

Protective effects of PACAP in ischemia

Pituitary adenylate cyclase activating polypeptide (PACAP) is an ubiquitous peptide involved, among others, in neurodevelopment, neuromodulation, neuroprotection, neurogenic inflammation and nociception. Presence of PACAP and its specific receptor, PAC1, in the trigeminocervical complex, changes of PACAP levels in migraine patients and the migraine-inducing effect of PACAP injection strongly support the involvement of PACAP/PAC1 receptor in migraine pathogenesis. While antagonizing PAC1 receptor is a promising therapeutic target in migraine, the diverse array of PACAP's functions, including protection in ischemic events, requires that the cost-benefit of such an intervention is well investigated by taking all the beneficial effects of PACAP into account. In the present review we summarize the protective effects of PACAP in ischemia, especially in neuronal ischemic injuries, and discuss possible points to consider when developing strategies in migraine therapy interfering with the PACAP/PAC1 receptor system.

PACAP38 in human models of primary headaches

Background

To review the role of PACAP38 in human models of primary headaches, discuss possible mechanisms of PACAP38-induced migraine, and outline future directions.

Discussion

Experimental studies have established PACAP38 as a potent pharmacological “trigger” molecule of migraine-like attacks. These studies have also revealed a heterogeneous PACAP38 migraine response in migraine without aura patients. In addition, findings from brain imaging studies have demonstrated neuronal and vascular changes in migraine patients both ictally and interictally after PACAP38 infusion.

Conclusion

Human migraine models have shed light on the importance of PACAP38 in the pathophysiology of primary headaches. These studies have also pointed to the PAC₁ receptor and the PACAP38 molecule itself as target sites for drug testing. Future research should seek to understand the mechanisms underlying PACAP38-induced migraine. The results from an ongoing proof of concept randomized clinical trial may reveal the therapeutic potential of anti-PAC₁ receptor antibodies for migraine prevention.

Pituitary Adenylate Cyclase Activating Peptide (1-38) and its analog (Acetyl-[Ala15, Ala20] PACAP 38-polyamide) reverse methacholine airway hyperresponsiveness in rats

The aim of this study was to investigate both functionally and structurally bronchodilator effects of Pituitary adenylate cyclase activating peptide (PACAP38) and acetyl-[Ala15, Ala20] PACAP38-polyamide, a potent PACAP38 analog, in rats challenged by methacholine (MeCh). Male Wistar rats were divided randomly into five groups. Groups 1 and 2 inhaled respectively aerosols of saline or increasing doses of MeCh (0.5, 1, 2.12, 4.25, 8.5, 17, 34 and 68mg/L). The other groups received terbutaline (Terb) (250 µg/rat) (10-6 M), PACAP38 (50 µg/rat) (0.1 mM) or PACAP38 analog (50 µg/rat) associated to MeCh from the dose of 4.25 mg/L. Total lung resistances (RL) were recorded before and 2 min after MeCh administration by pneumomultitest equipment. MeCh administration induced a significant and a dose-dependent increase (p<0.05) of RL compared to control rats. Terb, PACAP38 and PACAP38 analog reversed significantly the MeCh-induced bronchial constriction, smooth muscle (SM) layer thickness and bronchial lumen mucus abundance. PACAP38 analog prevents effectively bronchial smooth muscle layer thickness, mucus hypersecretion and lumen decrease. Therefore, it may constitute a potent therapeutic bronchodilator.

Pituitary adenylate cyclase-activating peptide receptor 1 mediates anti-inflammatory effects in allergic airway inflammation in mice

BACKGROUND

Bronchial asthma is characterized by airway inflammation and reversible obstruction. Since the gold standard of therapy, a combination of anti-inflammatory corticosteroids and bronchodilatory β(2) agonists, has recently been discussed to be related to an increased mortality, there is a need for novel therapeutic pathways.

OBJECTIVE

A new experimental concept that encompasses the vasoactive intestinal peptide/pituitary adenylate cyclase activating peptide (PACAP) family of receptors by demonstrating the anti-inflammatory effects of the PACAP receptor 1 (PAC1R) in a murine model of allergic asthma is described.

METHODS

PAC1R expression was investigated in lung tissue and isolated dendritic cells (DCs) via real-time PCR. Ovalbumin (OVA)-induced asthma models were used in PAC1R-deficient mice and BALB/c mice treated with PAC1R agonist maxadilan (MAX). Bronchoalveolar lavages have been performed and investigated at the cellular and cytokine levels. Fluorescence staining of a frozen lung section has been performed to detect eosinophil granulocytes in lung tissue. Plasma IgE levels have been quantified via the ELISA technique. Lung function was determined using head-out body plethysmography or whole-body plethysmography.

RESULTS

Increased PAC1R mRNA expression in lung tissue was present under inflammatory conditions. PAC1R expression was detected on DCs. In OVA-induced asthma models, which were applied to PAC1R-deficient mice (PAC1R(-/-)) and to BALB/c mice treated with the specific PAC1R agonist MAX, PAC1R deficiency resulted in inflammatory effects, while agonistic stimulation resulted in anti-inflammatory effects. No effects on lung function were detected both in the gene-depletion and in the pharmacologic studies. In summary, here, we demonstrate that anti-inflammatory effects can be achieved via PAC1R.

CONCLUSION

PAC1R agonists may represent a promising target for an anti-inflammatory therapy in airway diseases such as bronchial asthma.

PACAP is transiently expressed in anterior pituitary gland of rats: in situ hybridization and cell immunoblot assay studies

In this work the expression of PACAP (pituitary adenylate cyclase activating polypeptide) in rat anterior pituitary was demonstrated for the first time using in situ hybridization. The number of cells showing PACAP signal in intact male rats was negligible similarly to that of diestrous rats. In proestrous rats sacrificed at 10h there was a moderate increase in the expression and after a decrease at 16 h and 18 h, there was a transient peak at 20 h and then the number of labeled cells was declined again (22 h). In the cell immunoblot assay study it was observed that the number of PACAP blot forming (PACAP releasing) cells in an anterior pituitary cell culture changed according to a similar pattern as the number of PACAP expressing cells. The number of blots was also the highest when the animals were sacrificed in the evening of proestrus at 20h. The results obtained by in situ hybridization and cell immunoblot assay well correlate with each other. The above-mentioned results support our hypothesis that the enhanced expression and secretion of PACAP in the pituitary gland may be involved in ceasing the LH surge.

Mediators and modulators of pulmonary arterial hypertension

Pulmonary hypertension (PH), defined as a mean pulmonary arterial (PA) pressure of >25 mmHg at rest or >30 mmHg during exercise, is characterized by a progressive and sustained increase in pulmonary vascular resistance that eventually leads to right ventricular failure. Clinically, PH may result from a variety of underlying diseases (Table 1 and Refs. 50, 113, 124). Pulmonary arterial hypertension (PAH) may be familial (FPAH) or sporadic (idiopathic, IPAH), formerly known as primary pulmonary hypertension, i.e., for which there is no demonstrable cause. More often, PAH is due to a variety of identifiable diseases including scleroderma and other collagen disorders, liver disease, human immunodeficiency virus, and the intake of appetite-suppressant drugs such as phentermine and fenfluramine (72). Other, more common, causes of PAH include left ventricular failure (perhaps the most common cause), valvular lesions, chronic pulmonary diseases, sleep-disordered breathing, and prolonged residence at high altitude. This classification, now widely accepted, was first proposed at a meeting in Evian, France, in 1998, and modified in Venice, Italy, in 2003 (124).

Potential protective action of pituitary adenylate cyclase-activating polypeptide (PACAP38) on in vitro and in vivo models of myeloma kidney injury

The most common type of renal injury in multiple myeloma is chronic tubulointerstitial nephropathy associated with casts in tubule lumens, an entity referred to as “myeloma kidney” that often progresses to end-stage kidney diseases. Myeloma kidney is associated with a significant increase in all-cause mortality, yet no effective intervention, except a limited use of steroid, is available. Here, we report that pituitary adenylate cyclase-activating polypeptide with 38 residues (PACAP38) dramatically prevents injury of cultured renal proximal tubule cells caused by myeloma light chains through suppression of proinflammatory cytokines production, by inhibiting p38 MAPK and translocation of NFκB via both PAC1 and VPAC1 receptors. The suppressive effects of PACAP was as effective as dexamethasone in all of their cytokine assays and demonstrated both in vitro and in vivo. Furthermore, PACAP38 inhibits myeloma cell growth directly and may also indirectly by suppressing production of the growth factor, IL-6, from bone marrow stromal cells, that is stimulated by adhesion of myeloma cells. These findings render PACAP38 worth evaluation as a promising candidate for an effective and safe renoprotectant in myeloma kidney, and possibly other nephropathy, and also as a new antitumor agent in multiple myeloma.

Effect of PACAP on LH release studied by cell immunoblot assay depends on the gender, on the time of day and in female rats on the day of the estrous cycle

We have previously demonstrated that pituitary adenylate cyclase activating polypeptide (PACAP) can be released from cultured rat anterior pituitary cells and when added to the medium in physiological concentration it releases LH from individual gonadotropes. In the present work, we studied whether the release of PACAP and the responsiveness of LH cells to PACAP depend on the gender, on the time of day when the animals were sacrificed, and in females on the stage of the estrous cycle. Anterior pituitary cells were cultured on nitrocellulose membrane. We found that the number of PACAP releasing cells was higher in proestrous than in diestrous female or in male rats and their number was always higher in the evening than at the other times. The effect of PACAP on LH cells was stimulatory in the morning of proestrus and diestrus. In proestrous rats, PACAP did not influence LH release in the afternoon or the evening, but in diestrous rats it decreased it in the afternoon and the evening. In males, there was a decrease of LH due to PACAP treatment at 10 and 20 h; however, PACAP did not influence LH at 16 h. It was concluded that in vivo PACAP might be involved in the circadian and episodic release of LH at pituitary level.

Pulmonary Hypertension and Right Heart Failure in Pituitary Adenylate Cyclase–Activating Polypeptide Type I Receptor–Deficient Mice

Background— Pituitary adenylate cyclase–activating polypeptide (PACAP), acting via 3 different G protein–coupled receptors, has been implicated in the regulation of several homeostatic systems in the body, including cardiopulmonary control. To define the physiologic role of the PACAP-preferring type I receptor, PAC1, in cardiopulmonary function, we developed a mutant mouse strain lacking functional PAC1 receptors.

Methods and Results— When PAC1-deficient mice were crossed onto a C57BL/6 background, almost all mutants died during the second postnatal week. Whereas mutant mice were indistinguishable from their wild-type littermates at birth, they showed progressive weakness and died from rapidly developing heart failure. Right ventricles of PAC1 mutants were massively dilated and showed cardiac myocyte hypertrophy, whereas left ventricular structure was unaltered. On direct cardiac catheterization, right ventricular pressure was elevated by 45% in PAC1-deficient mice, indicating increased pulmonary artery pressure, as no malformations were detected in the valves or outflow tract of the right ventricle. Consistent with elevated pulmonary pressure, lung capillary density was decreased by 30% and small pulmonary arteries of mutant mice had significant vascular smooth muscle cell hypertrophy compared with wild-type mice.

Conclusions— Whereas PACAP induces vasodilation in isolated pulmonary vessels in wild-type mice, the absence of its specific receptor PAC1 causes pulmonary hypertension and right heart failure after birth. These in vivo findings demonstrate the crucial importance of PAC1-mediated signaling for the maintenance of normal pulmonary vascular tone during early postnatal life.

Distribution of PACAP-38 in the central nervous system of various species determined by a novel radioimmunoassay

Pituitary adenylate cyclase activating polypeptide (PACAP) occurs in two molecular forms: PACAP-38 and PACAP-27. Soon after the isolation and chemical characterization of PACAP, the first radioimmunoassay (RIA) methods have been developed, but it is a still rarely used laboratory technique in the field of PACAP research. The aim of the present study was to develop a novel, highly specific PACAP-38 assay to investigate the quantitative distribution of PACAP-38 in the central nervous system of various vertebrate species under the same technical and experimental conditions. Different areas of the brain and the spinal cord were removed from rats, chickens and fishes and the tissue samples were processed for PACAP-38 RIA. Our results indicate that the antiserum used in the RIA is C-terminal specific, without affinity for other members of the vasoactive intestinal polypeptide (VIP)/secretin/glucagon peptide family. The average ID50 value was 48.6+/-3.4 fmol/ml determined in 10 consecutive assays. Detection limit for PACAP-38 proved to be 2 fmol/ml. PACAP-38 immunoreactivity was present in the examined brain areas of each species studied, with highest concentration in the rat diencephalons. High levels of PACAP-38 were also detected in the rat telencephalon, followed by spinal cord and brainstem. The central nervous system of the fish also contained considerable concentrations of PACAP-38, whereas lowest concentrations were measured in the central nervous system of the chicken.

[Physiological and therapeutic roles of PACAP in glucose metabolism and diabetes]

Pituitary adenylate cyclase activating polypeptide (PACAP) is a ubiquitous neuropeptide in the central and peripheral nervous systems. Previously we reported that PACAP38 is localized in pancreatic islets and serves as an endogenous amplifier of glucose-induced insulin secretion. PACAP activates Gs-cAMP system, stimulates voltage-dependent Ca(2+) channels, and increases cytosolic Ca(2+) concentration in beta-cells. On the other hand, PAC1 receptor is expressed in adipocytes. PACAP enhances insulin-stimulated glucose uptake in an adipocyte cell-line, 3T3-L1 cells. PACAP does not alter the tyrosine phosphorylation of insulin receptor and IRS-1, but increases the activity of PI-3 kinase, a distal site of insulin signaling. PACAP also promotes differentiation of 3T3-L1 cells from fibroblasts to adipocytes. In GK rats, an animal model of type 2 diabetes, daily i.p. injection of PACAP38 (6 pmol/kg) from the age of 3 weeks prevents development of hyperglycemia between 3 to 8 weeks. These results demonstrate that PACAP enhances glucose-stimulated insulin secretion in islets, enhances insulin action inadipocytes, and prevents hyperglycemia in diabetic animals. This finding presents a possible therapeutic use of PACAP in the treatment of diabetes.

Neurotransmitters co-existing with VIP or PACAP

It is now recognized that a neuron can produce, store and release more than one transmitter substance, and a number of examples of co-existing transmitters, particularly a neuropeptide together with a classical transmitter, have been reported. The present paper deals with transmitter substances, peptides or classical transmitters, co-existing with the two structurally related peptides VIP and PACAP and the possible functional implications of this co-existence.

The diffuse endocrine system: from embryogenesis to carcinogenesis

In the present review we will summarise the current knowledge about the cells comprising the Diffuse Endocrine System (DES) in mammalian organs. We will describe the morphological, histochemical and functional traits of these cells in three major systems gastrointestinal, respiratory and prostatic. We will also focus on some aspects of their ontogeny and differentiation, as well as to their relevance in carcinogenesis, especially in neuroendocrine tumors. The first chapter describes the characteristics of DES cells and some of their specific biological and biochemical traits. The second chapter deals with DES in the gastrointestinal organs, with special reference to the new data on the differentiation mechanisms that leads to the appearance of endocrine cells from an undifferentiated stem cell. The third chapter is devoted to DES of the respiratory system and some aspects of its biological role, both, during development and adulthood. Neuroendocrine hyperplasia and neuroendocrine lung tumors are also addressed. Finally, the last chapter deals with the prostatic DES, discussing its probable functional role and its relevance in hormone-resistant prostatic carcinomas.

Pituitary adenylate cyclase-activating polypeptide, effects in the human nose

BACKGROUND

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide with strong vaso- and bronchodilator capacity. There is recent evidence that PACAP decreases the release of proinflammatory cytokines and we have previously shown that PACAP inhibits neutrophil chemotaxis in vitro, but little is known about the effects of PACAP in human upper and lower airways.

OBJECTIVE

To investigate the effects of PACAP in the human upper respiratory tract focusing on vasodilatation/nasal airway resistance (NAR), neutrophil recruitment, plasma extravasation and endogenous production of IL-1-related mediators.

METHODS

Surgical specimens from five patients (aged 19-55 years), obtained in conjunction with nasal surgery, were used for immunohistochemical localization of PACAP in the nasal mucosa. In seven, healthy, non-allergic, non-smoking subjects (aged 19-45 years), NAR was measured with rhinomanometry. Nasal lavage was performed, before and after intranasal application of PACAP (200 microL of a 1 microm PACAP solution in each nasal cavity), with and without the addition of histamine. Cells, albumin and IL-1-related mediators were analysed in nasal lavage. In addition, the effects on pulse, blood pressure, ECG and pulmonary function were evaluated.

RESULTS

In the nasal mucosa, PACAP-like immunoreactive nerve fibres were seen close to blood vessels and seromucous glands. Application of PACAP in the nasal cavity increased NAR and augmented the increase in NAR induced by histamine. In addition, PACAP inhibited histamine-induced recruitment of neutrophils, increased plasma leakage and reduced the level of IL-1RA (an endogenously produced IL-1 receptor antagonist) in nasal lavage. Cardiovascular and pulmonary parameters were not affected.

CONCLUSION

These results imply that PACAP is an important endogenous mediator in human upper airways, with a potential role as a regulator of vascular smooth muscle, secretion, plasma extravasation, neutrophil recruitment and cytokine activity.

Pituitary adenylate cyclase-activating peptide in the rat central nervous system: an immunohistochemical and in situ hybridization study

In the present study the localization of pituitary adenylate cyclase-activating peptide (PACAP)-expressing cell bodies and PACAP projections were mapped in the adult rat brain and spinal cord by using immunohistochemistry and in situ hybridization histochemistry. A widespread occurrence of PACAP-containing cell bodies was found, with the greatest accumulation in several hypothalamic nuclei and in several brainstem nuclei, especially the habenular nuclei, the pontine nucleus, the lateral parabrachial nucleus (LPB), and the vagal complex. PACAP was also present in cell bodies in the olfactory areas, in neocortical areas, in the hippocampus, in the vestibulo- and cochlear nuclei, in cell bodies of the intermediolateral cell column of the spinal cord and in Purkinje cells of the cerebellum, in the subfornical organ, and in the organum vasculosum of the lamina terminalis. An intense accumulation of PACAP-immunoreactive (-IR) nerve fibers was observed throughout the hypothalamus, in the amydaloid and extended amygdaloid complex, in the anterior and paraventricular thalamic nuclei, in the intergeniculate leaflet, in the pretectum, and in several brainstem nuclei, such as the parabrachial nucleus, the sensory trigeminal nucleus, and the nucleus of the solitary tract. PACAP-IR nerve fibers were also found in the area postrema, the posterior pituitary and the choroid plexus, and the dorsal and ventral horn of the spinal cord. The widespread distribution of PACAP in the brain and spinal cord suggests that PACAP is involved in the control of many autonomic and sensory functions as well as higher cortical processes.

Neonatal PACAP administration in rats delays puberty through the influence of the LHRH neuronal system

The onset of puberty is a concerted action of many factors which leads to cyclic LHRH release in rats. It has been demonstrated that; in common with vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase activating polypeptide (PACAP) is also involved in the differentiation of the central nervous system. In our previous work, it was shown that a single PACAP injection into neonatal female rats delayed puberty. In the present work, neonatal administration of PACAP delayed the vaginal opening and decreased the weight of anterior pituitaries, the number of expelled ova at the first ovulation and the intensity of LHRH immunostaining in the septo-preoptico-infundibular system. PACAP antiserum had a reverse effect on LHRH immunoreactivity. The other studied parameters in the latter group remained unchanged compared to control rats. It was concluded that neonatal PACAP administration delayed the onset of puberty through the influence of the LHRH neuronal system.

Distribution of PACAP and its mRNA in several nonneural tissues of rats demonstrated by sandwich enzyme immunoassay and RT-PCR technique

The presence of PACAP in various organs was previously demonstrated using immunohistochemistry and radioimmunoassay. The aim of our work was to get information whether the presence of immunoreactive PACAP in various organs, mainly in the gastric mucosa, also indicates the place of its synthesis. The immunoreactive PACAP and its mRNA were measured in parallel assays using sandwich enzyme immunoassay (S-EIA) and RT-PCR technique. PACAP and its mRNA were demonstrated in the pancreas, testes, adrenal glands, ovaries, and in the oxyntic mucosa of the stomach. These results support our previous observation that PACAP is present not only in the nervous system and endocrine glands, but might be synthetized in the oxyntic mucosa of the stomach as well.

Pituitary adenylate cyclase-activating peptide and lung-liquid reabsorption in vitro by lungs from fetal guinea-pigs

Pituitary adenylate cyclase-activating peptide (PACAP) is present in the lungs, notably in their internal neuroendocrine system; however, its use is not clear. It was investigated for its possible ability to cause lung-liquid reabsorption around birth. Lungs from 31 late-term fetal guinea-pigs (at 60 ± 2 days of gestation) were supported in vitro for 3 h; lung-liquid movements were monitored by a dye-dilution method. Untreated control preparations (n = 9) produced fluid at 1.85 ± 0.40 mL·kg–1 body mass·h–1 (mean ± SD), with no significant change (ANOVA, regression analysis). Those given 10–8 M PACAP in the middle hour turned to reabsorption (n = 3) or reduced production markedly (n = 3) (average fall 84.4 ± 5.4%; significant at P < 0.001–0.0005); effects continued and increased after the PACAP was removed. Preparations given 10–9 M PACAP reacted similarly, but there was partial recovery after treatment (five reabsorbed, four reduced production; average fall 91.4 ± 14.3%; significant at P < 0.01–0.0005). Preparations given 10–10 M PACAP all reduced production, with partial recovery (average fall 43.5 ± 8.2%; significant at P < 0.005–0.0005). Preparations given 10–11 M PACAP showed little or no effect. The linear log dose–response curve became maximal at 10–9 M (r2 = 0.98; theoretical threshold 10–13 M). The results increase the likelihood that the neuroendocrine system is important in lung-liquid reabsorption, and suggest that PACAP could combine its relaxation of airways with lung-liquid removal, and therefore aid the first attempts of the newborn to breathe.

Phospholipids modulate the biophysical properties and vasoactivity of PACAP-(1--38)

The purpose of this study was to elucidate the interactions between pituitary adenylate cyclase-activating peptide (PACAP)-(1--38) and phospholipids in vitro and to determine whether these phenomena modulate, in part, the vasorelaxant effects of the peptide in the intact peripheral microcirculation. We found that the critical micellar concentration of PACAP-(1--38) was 0.4-0.9 microM. PACAP-(1--38) significantly increased the surface tension of a dipalmitoylphosphatidylcholine monolayer and underwent conformational transition from predominantly random coil in saline to alpha-helix in the presence of distearoyl-phosphatidylethanolamine-polyethylene glycol (molecular mass of 2,000 Da) sterically stabilized phospholipid micelles (SSM) (P < 0.05). Using intravital microscopy, we found that aqueous PACAP-(1--38) evoked significant concentration-dependent vasodilation in the intact hamster cheek pouch that was significantly potentiated when PACAP-(1--38) was associated with SSM (P < 0.05). The vasorelaxant effects of aqueous PACAP-(1--38) were mediated predominantly by PACAP type 1 (PAC(1)) receptors, whereas those of PACAP-(1--38) in SSM predominantly by PACAP/vasoactive intestinal peptide type 1 and 2 (VPAC(1)/VPAC(2)) receptors. Collectively, these data indicate that PACAP-(1--38) self-associates and interacts avidly with phospholipids in vitro and that these phenomena amplify peptide vasoactivity in the intact peripheral microcirculation.

The neuropeptide pituitary adenylate cyclase-activating polypeptide and islet function

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is ubiquitously distributed in both the central and peripheral nervous systems and exerts a variety of effects. PACAP is a neuropeptide in pancreatic islets, where it has been suggested as a parasympathetic and sensory neurotransmitter. PACAP stimulates insulin secretion in a glucose-dependent manner, by an effect executed mainly through augmenting the formation of cAMP and stimulating the uptake of calcium. Accumulating evidence in animal studies points to a physiological importance of PACAP in the regulation of the insulin response to feeding. This review summarizes the current knowledge of islet actions and mechanisms and the function of PACAP.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Pituitary adenylate cyclase activating peptide mediates inhibitory nonadrenergic noncholinergic relaxation

We investigated the contribution of pituitary adenylate cyclase activating peptide (PACAP) to inhibitory nonadrenergic noncholinergic (inhibitory-NANC) relaxation of tracheal smooth muscle in cats. We also investigated the roles of vasoactive intestinal peptide (VIP) and nitric oxide (NO) on this function. Smooth muscle strips prepared from feline trachea were precontracted with 1 microM serotonin, and inhibitory-NANC relaxation was induced by electrical-field stimulation in the presence of atropine and propranolol. PACAP-(6-38) (a selective antagonist of PACAP; 1, 3 and 10 microM), VIP-(10-28) (a selective antagonist of VIP; 1, 3 and 10 microM) and N(omega)-nitro-L-arginine methyl ester (L-NAME, a selective NO synthase inhibitor; 3, 10 and 30 microM) each partially but significantly attenuated the amplitude of inhibitory-NANC relaxation. The effects of PACAP-(6-38) and VIP-(10-28) were additive. Addition of PACAP-(6-38) and/or VIP-(10-28) further attenuated relaxation in the presence of L-NAME. These results suggest that PACAP, VIP and NO contribute to the relaxation induced by inhibitory-NANC in tracheal smooth muscle in cats, and that they mediate this relaxation via different pathways.

Immunohistochemical localization and distribution of VIP/PACAP receptors in human lung

VIP and PACAP are distributed in nerve fibers throughout the respiratory tract acting as potent bronchodilators and secretory agents. By using RT-PCR and immunoblotting techniques, we have previously shown the expression of common VIP/PACAP (VPAC(1) and VPAC(2)) and specific PACAP (PAC(1)) receptors in human lung. Here we extend our aims to investigate by immunohistochemistry their localization and distribution at this level. A clear immunopositive reaction was obtained in human lung sections by using either anti-VPAC(1) or -VPAC(2) receptor antibodies but not with anti-PAC(1) receptor antibody. However, PAC(1) receptor (and VPAC(1) and VPAC(2) receptors) could be identified in lung membranes by immunoblotting which supports that the PAC(1) receptor is expressed at a low density. Both VPAC(1) and VPAC(2) receptors showed similar immunohistochemical patterns appearing in smooth muscle cells in the wall of blood vessels and in white blood cells (mainly in areas with inflammatory responses). The results agree with previous evidence on the importance of both peptides in the immune system and support their anti-inflammatory and protective roles in lung.

Effect of vasoactive intestinal peptide (VIP)-related peptides on cholinergic neurogenic and direct mucus secretion in ferret trachea in vitro

1 We investigated whether vasoactive intestinal peptide (VIP) and its related peptides, pituitary adenylate cyclase activating peptide (PACAP) and secretin, regulate cholinergic neural mucus secretion in ferret trachea in vitro, using 35SO4 as a mucus marker. We also studied the interaction between VIP and secretin on cholinergic mucus output. 2 VIP (1 and 10 microM) increased secretion, whereas neither PACAP1 - 27, PACAP1 - 38 nor secretin (up to 10 microM) increased mucus output. In contrast, VIP, PACAP1 - 27 and PACAP1 - 38 concentration-dependently inhibited cholinergic neural secretion, with an order of potency of VIP>PACAP 1 - 38>PACAP1 - 27. Neither PACAP1 - 27 nor PACAP1 - 38 altered the secretion induced by acetylcholine (ACh). 3 Secretin increased cholinergic neural secretion with a maximal increase of 190% at 1 microM. This potentiation was blocked by VIP or atropine. Similarly, secretin (1 microM) potentiated VIP (1 microM)-induced mucus output by 160%. Secretin did not alter exogenous ACh-induced secretion. VIP vs secretin competition curves suggested these two peptides were competing reversibly for the same receptor. 4 We conclude that, in ferret trachea in vitro, VIP and PACAPs inhibit cholinergic neural secretion via pre-junctional modulation of cholinergic neurotransmission. VIP and secretin compete for the same receptor, possibly a VIP1 receptor, at which secretin may be a receptor antagonist.

Molecular cloning and expression of a chicken pituitary adenylate cyclase-activating polypeptide receptor

Although, since the isolation of pituitary adenylate cyclase-activating polypeptide (PACAP), a wealth of literature has been published describing its localization, binding sites, and biological activities in a variety of mammalian tissues, only very little is known about PACAP in avian species. Therefore, in order to find out the sites of actions of PACAP and to elucidate its physiological significance in birds, we identified a chicken PACAP receptor homologue of the mammalian type I receptors (PAC(1)-Rs). The chicken PACAP type I cDNA sequence was obtained using reverse transcriptase-polymerase chain reaction (RT-PCR) in combination with 3'- and 5'-RACE PCR. This cDNA encodes a 471 amino acid precursor protein, sharing 81-83% sequence identity with mammalian analogs and 76% amino acid identity with the goldfish type I PACAP receptor. Northern blot analysis of chicken brain poly(A)(+)-rich RNA revealed the presence of a 5.5 kb and 7.5 kb PAC(1) receptor transcript. RT-PCR revealed that the chicken PACAP receptor is mainly expressed in the brain and gonads. A smaller amount of the receptor mRNA was found in pituitary, adrenal gland, kidney, intestine, pancreas, lung, and heart tissue. In situ hybridization with specific antisense oligodeoxynucleotide probes showed a widespread distribution of PAC(1) receptor mRNA in the chicken brain, with the highest expression being found in the dorsal telencephalon, olfactory bulb, hypothalamus, optic tectum, and cerebellar cortex. These findings suggest that PACAP affect a variety of functions both in the brain and peripheral tissues of the chicken.

Pituitary adenylate cyclase-activating polypeptide receptors during development: expression in the rat embryo at primitive streak stage

The distribution and localization of the pituitary adenylate cyclase-activating polypeptide (PACAP) receptor the PAC1 receptor (previously called the type 1 PACAP receptor or PVR1), which binds PACAP, but not vasoactive intestinal peptide, with high affinity] were first investigated in rats with in situ hybridization for its messenger RNA, and with immunohistochemical methods during prenatal and postnatal development. The expression of PACAP receptor messenger RNA was first detected in the rat embryo at the primitive streak stage as early as embryonic day 9, and it was intensely expressed in the neural plate. PACAP receptor messenger RNA was also intensely expressed in the neuroepithelia of the mesencephalon and rhombencephalon at embryonic day 11, and expressed in the basal telencephalon, hippocampal formation neuroepithelium, cortical neuroepithelium and cerebellar neuroepithelium after embryonic day 13. It was also expressed in the olfactory bulb neuroepithelium after embryonic day 16, and in mature regions of the older embryos. In postnatal developing brains, PACAP receptor messenger RNA was intensely expressed in the olfactory bulb, hippocampal formation, cerebellum and other scattered regions. The localization of PACAP receptor-like immunoreactivity coincided well with that of the gene transcripts. We also used reverse transcription-polymerase chain reaction methods to determine the expression of the splice variants of the PACAP receptor gene. At each ontogenetic stage of the rat from embryonic day 9 to postnatal day 60, two major products were detected with reverse transcription-polymerase chain reaction, a thick band (303 base pairs) corresponding to the short splice variant of the receptor that lacks both the "hip" and "hop" cassettes, and a thin band (387 base pairs) corresponding to the splice variant that contains one cassette of "hop" or "hip". There was no evidence for the other larger splice variants. Some of the amplified products were sequenced and found to have the exact sequences of "PACAP receptor" and "PACAP receptor-hopl", which are coupled to different signal transduction pathways. These results indicate that the PACAP receptor is actively expressed in different neuroepithelia from early developmental stages and expressed in various brain regions during prenatal and postnatal development, and that the major splice variants are "PACAP receptor" and "PACAP receptor-hopl". The initial mapping of ontogenetic localization of the PACAP receptor provides the basis for a better understanding of the functions of PACAP and its receptors during the development of the brain.

Expression, pharmacological, and functional evidence for PACAP/VIP receptors in human lung

Pituitary adenylate cyclase-activating peptide (PACAP) type 1 (PAC(1)) and common PACAP/vasoactive intestinal peptide (VIP) type 1 and 2 (VPAC(1) and VPAC(2), respectively) receptors were detected in the human lung by RT-PCR. The proteins were identified by immunoblotting at 72, 67, and 68 kDa, respectively. One class of PACAP receptors was defined from (125)I-labeled PACAP-27 binding experiments (dissociation constant = 5.2 nM; maximum binding capacity = 5.2 pmol/mg protein) with a specificity: PACAP-27 approximately VIP > helodermin approximately peptide histidine-methionine (PHM) >> secretin. Two classes of VIP receptors were established with (125)I-VIP (dissociation constants of 5.4 and 197 nM) with a specificity: VIP approximately helodermin approximately PACAP-27 >> PHM >> secretin. PACAP-27 and VIP were equipotent on adenylyl cyclase stimulation (EC(50) = 1.6 nM), whereas other peptides showed lower potency (helodermin > PHM >> secretin). PACAP/VIP antagonists supported that PACAP-27 acts in the human lung through either specific receptors or common PACAP/VIP receptors. The present results are the first demonstration of the presence of PAC(1) receptors and extend our knowledge of common PACAP/VIP receptors in the human lung.

Pituitary adenylate cyclase-activating polypeptide and islet amyloid polypeptide in primary sensory neurons: functional implications from plasticity in expression on nerve injury and inflammation

Primary sensory neurons serve a dual role as afferent neurons, conveying sensory information from the periphery to the central nervous system, and as efferent effectors mediating, e.g., neurogenic inflammation. Neuropeptides are crucial for both these mechanisms in primary sensory neurons. In afferent functions, they act as messengers and modulators in addition to a principal transmitter; by release from peripheral terminals, they induce an efferent response, "neurogenic inflammation," which comprises vasodilatation, plasma extravasation, and recruitment of immune cells. In this article, we introduce two novel members of the sensory neuropeptide family: pituitary adenylate cyclase-activating polypeptide (PACAP) and islet amyloid polypeptide (IAPP). Whereas PACAP, a vasoactive intestinal polypeptide-resembling peptide, predominantly occurs in neuronal elements, IAPP, which is structurally related to calcitonin gene-related peptide, is most widely known as a pancreatic beta-cell peptide; as such, it has been recognized as a constituent of amyloid deposits in type 2 diabetes. In primary sensory neurons, under normal conditions, both peptides are predominantly expressed in small-sized nerve cell bodies, suggesting a role in nociception. On axotomy, the expression of PACAP is rapidly induced, whereas that of IAPP is reduced. Such a regulation of PACAP suggests that it serves a protective role during nerve injury, but that of IAPP may indicate that it is an excitatory messenger under normal conditions. In contrast, in localized adjuvant-induced inflammation, expression of both peptides is rapidly induced. For IAPP, studies in IAPP-deficient mice support the notion that IAPP is a pronociceptive peptide, because these mutant mice display a reduced nociceptive response when challenged with formalin.

The pulmonary neuroendocrine system: the past decade

The pulmonary neuroendocrine system consists of specialized airway endocrine epithelial cells, associated with nerve fibres. The epithelial cells, the pulmonary neuroendocrine cells (PNEC), can be solitary or clustered to form neuroepithelial bodies (NEB). During the last thirty years, the pulmonary neuroendocrine system has been intensively investigated and much knowledge of its function has been obtained. This text reviews work which dates from the last ten years. In this period, the picture of the pulmonary neuroendocrine system we previously had, has not fundamentally changed. The pulmonary neuroendocrine system is still regarded as an oxygen sensitive chemoreceptor with local and reflex-mediated regulatory functions, and as a regulator of airway growth and development. Continuing research has much more refined this picture. This text reviews several aspects of the pulmonary neuroendocrine system: phylogeny, the amine and peptide content of its epithelial cells, ontogeny and influence on lung development, the influence of hypoxia and nonhypoxic stimuli, immunomodulatory function, innervation and pathology. Among the discoveries of the past decade, three stand out prominently because of their great significance: additional proof that the neural component of the pulmonary neuroendocrine system is sensory, sound experimental evidence that PNEC stimulate airway epithelial cell differentiation and the discovery of a specific membrane oxygen receptor in the PNEC.

Hemodynamic actions of systemically injected pituitary adenylate cyclase activating polypeptide-27 in the rat

The aims of this study were (1) to characterize the hemodynamic mechanisms underlying the hypotensive effects of pituitary adenylate cyclase activating polypeptide-27 (PACAP-27 0.1-2.0 nmol/kg, i.v.) in pentobarbital-anesthetized rats, and (2) to determine the roles of the autonomic nervous system, adrenal catecholamines and endothelium-derived nitric oxide (NO) in the expression of PACAP-27-mediated effects on hemodynamic function. PACAP-27 produced dose-dependent decreases in mean arterial blood pressure and hindquarter and mesenteric vascular resistances in saline-treated rats. PACAP-27 also produced pronounced falls in mean arterial blood pressure in rats treated with the ganglion blocker, chlorisondamine (5 mg/kg, i.v.). The hypotensive and vasodilator actions of PACAP-27 were not attenuated by the beta-adrenoceptor antagonist, propranolol (1 mg/kg, i.v.), or the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME 50 micromol/kg, i.v.). PACAP-27 produced dose-dependent increases in heart rate whereas the hypotensive response produced by the nitrovasodilator, sodium nitroprusside (10 microg/kg, i.v.), was associated with a minimal tachycardia. The PACAP-27-induced tachycardia was unaffected by chlorisondamine, but was virtually abolished by propranolol. These results suggest that the vasodilator effects of PACAP-27 are due to actions in the microcirculation rather than to the release of adrenal catecholamines and that this vasodilation may not involve the release of endothelium-derived NO. These results also suggest that PACAP-27 produces tachycardia by directly releasing norepinephrine from cardiac sympathetic nerve terminals rather than by direct or baroreceptor reflex-mediated increases in sympathetic nerve activity.

Perspectives on pituitary adenylate cyclase activating polypeptide (PACAP) in the neuroendocrine, endocrine, and nervous systems

PACAP is a pleiotropic neuropeptide that belongs to the secretin/glucagon/VIP family. PACAP functions as a hypothalamic hormone, neurotransmitter, neuromodulator, vasodilator, and neurotrophic factor. Its structure has been remarkably conserved during evolution. The PACAP receptor is G protein-coupled with seven transmembrane domains and also belongs to the VIP receptor family. PACAP, but not VIP, binds to PAC1-R, whereas PACAP and VIP bind to VPAC1-R and VPAC2-R with a similar affinity. Despite the sizable homology of the structures of PACAP and VIP and their receptors, the distribution of these peptides and receptors is quite different. At least eight subtypes of PACAP specific, or PAC1-R, result from alternate splicing. Each subtype is coupled with specific signaling pathways, and its expression is tissue or cell specific. Although PACAP fulfills most requirements for a physiological hypothalamic hypophysiotropic hormone, it does not consistently stimulate secretion of the adenohypophysial hormones, except for stimulation of IL-6 release from the FS cells of the pituitary. The major regulatory role of PACAP in pituitary cells appears to be the regulation of gene expression of pituitary hormones and/or regulatory proteins that control growth and differentiation of the pituitary glandular cells. These effects appear to be exhibited directly and indirectly through a paracrine or autocrine action. Although PACAP stimulates the release of AVP, the physiological role of neurohypophysial PACAP remains unknown. One important action of PACAP in the endocrine system is its role as a potent secretagogue for adrenaline from the adrenal medulla through activation of TH. PACAP also stimulates the release of insulin and increases [Ca2+]i from pancreatic beta-cells at an extremely small concentration. The stage-specific expression of PACAP in testicular germ cells during spermatogenesis suggests its regulatory role in the maturation of germ cells. In the ovary, PACAP is transiently expressed in the granulosa cells of the preovulatory follicles and appears to be involved in the LH-induced cellular events in the ovary, including prevention of follicular apoptosis. In the central nervous system, PACAP acts as a neurotransmitter or neuromodulator, which has been supported by IHC and electrophysiological methods. More important, PACAP is a neurotrophic factor that may play an important role during the development of the brain. In the adult brain, PACAP appears to function as a neuroprotective factor that attenuates the neuronal damage resulting from various insults.

Pituitary adenylate cyclase activating peptides relax human pulmonary arteries by opening of KATP and KCa channels

BACKGROUND

Pituitary adenylate cyclase activating peptides (PACAPs) are potent endothelium independent dilators of human coronary arteries; however, their effects on human pulmonary arteries are unknown.

METHODS

The vasorelaxant effects of PACAP27 on human pulmonary segmental arteries were studied and the specific potassium (K+) channel regulatory mechanisms in the vasorelaxant effects were tested by means of isometric contraction experiments.

RESULTS

PACAP27 produced dose dependent relaxations of 10 microM rings preconstricted with prostaglandin F2 alpha (PGF2 alpha) with half maximal relaxation (IC50) at 17 nM. Pretreatment of the vessels with the ATP sensitive K+ (KATP) channel blocker glibenclamide (1 microM) or with the Ca2+ activated K+ (KCa) channel blocker iberiotoxin (100 nM) inhibited the PACAP27 induced relaxation.

CONCLUSIONS

These results provide evidence that PACAPs are potent vasodilators of human pulmonary arteries and that this relaxation might be mediated by opening of KATP and KCa channels.

PACAP and PACAP receptors in insulin producing tissues: localization and effects

We have studied the localization, receptor occupancy and potency of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) in insulin-producing tissues. Immunocytochemistry showed that PACAP-like immunoreactivity (PACAP-IR) was localized to pancreatic nerves with accumulation in intrapancreatic ganglia in both mouse and rat. In contrast, PACAP-IR could not be demonstrated in endocrine cells. Furthermore, in situ hybridization, using oligodeoxyribonucleotide probes recognizing mRNA for PACAP receptors, demonstrated that mouse and rat pancreas, and the insulinoma cell lines HIT-T15 and RINm5F, expressed both the PACAP type 1 and the VIP2/PACAP receptors. Moreover, both PACAP27 and PACAP38 dose-dependently (0.1 nM to 100 nM) and equipotently stimulated insulin secretion in isolated mouse and rat islets and in HIT-T15 and RINm5F cells. Furthermore, in mouse islets, vasoactive intestinal polypeptide (VIP) was of equal potency as PACAP at stimulating insulin secretion. In mouse, PACAP also stimulated insulin secretion in a subfraction of the isolated islets also at the low dose of 1 fM. Thus, (1) PACAP is exclusively a neuropeptide in the pancreas, (2) insulin-producing cells express PACAP type 1 and VIP2/PACAP receptors and (3) the two forms of PACAP equipotently stimulate insulin secretion. Based on these results, we suggest that PACAP is involved in the neural regulation of insulin secretion.

Embryonic expression of pituitary adenylate cyclase-activating polypeptide in sensory and autonomic ganglia and in spinal cord of the rat

Pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide that is related structurally to vasoactive intestinal polypeptide (VIP), has been shown to stimulate neuronal growth and differentiation, indicating a possible function in the development of the nervous system. Studies have indicated that the PACAP receptor is expressed during development, but data on PACAP expression are limited mainly to postnatal development. In the present study, we used immunohistochemistry and in situ hybridization histochemistry to examine the expression of PACAP in autonomic and sensory ganglia and spinal cord of rat fetuses at embryonic days 12-21 (E12-E21). PACAP immunoreactivity was visualized by using a specific monoclonal anti-PACAP antibody to detect both PACAP-38 and PACAP-27, and PACAP mRNA was visualized by using a [33P]-labeled cRNA-probe. PACAP- nerve fibers were observed in the spinal cord as early as E13. At E14, PACAP-immunoreactive nerve fibers projected to the sympathetic trunk, where few PACAP- nerve cell bodies were seen from E15. On the same embryonic day, PACAP-immunoreactive nerve cell bodies appeared in the intermediolateral column of the spinal cord. From E15 to E16, PACAP-immunoreactive nerve cell bodies were visible within sensory and autonomic ganglia, such as the dorsal root, the trigeminal, the sphenopalatine, the otic, the submandibular, and the nodose ganglia. At E16, PACAP+ nerve fibers were innervating the adrenal medulla, and immunoreactive fibers could also be observed in the superior cervical ganglion, in which PACAP-immunoreactive cell bodies were detected occasionally from E18. The synthesis of PACAP in neuronal cell bodies was confirmed by the demonstration of PACAP mRNA with in situ hybridization histochemistry. Thus, in all of the structures examined, PACAP appeared at roughly the same embryonic stage and, thereafter, increased to the adult level before birth. Because PACAP occurred with the same distribution pattern as that described in the adult rat, there is no evidence for transient expression. The early expression of PACAP suggests a possible role for the peptide in the developing nervous system.

Pituitary adenylate cyclase activating polypeptide immunoreactivity in capsaicin-sensitive nerve fibres supplying the rat urinary tract

Pituitary adenylate cyclase activating peptide is a new member of the vasoactive intestinal polypeptide family of peptides which is present in the brain as well as neuronal elements of a number of peripheral organs. Pituitary adenylate cyclase activating peptide occurs in two forms, pituitary adenylate cyclase activating peptide-38 and the C-terminally truncated 27 amino acid form, pituitary adenylate cyclase activating peptide-27, both derived from the same precursor which in addition gives rise to a structurally-related peptide, pituitary adenylate cyclase activating peptide-related peptide. Using specific radioimmunoassays for pituitary adenylate cyclase activating peptide-38, pituitary adenylate cyclase activating peptide-27 and pituitary adenylate cyclase activating peptide-related peptide we found that all three pituitary adenylate cyclase activating peptide-precursor-derived peptides were present in tissue extracts from the ureter, the urinary bladder and the urethra. Pituitary adenylate cyclase activating peptide-38 was the dominating peptide with the highest concentration in the ureter. When extracts from the urinary bladder were fractionated by reverse phase high pressure liquid chromatography immunoreactive components corresponding to synthetic pituitary adenylate cyclase activating peptide-38, pituitary adenylate cyclase activating peptide-27 and pituitary adenylate cyclase activating peptide-related peptide were identified with the respective antisera. By immunohistochemistry, using a specific monoclonal mouse anti-pituitary adenylate cyclase activating peptide antibody, pituitary adenylate cyclase activating peptide-immunoreactivity was shown to have a widespread distribution in the rat urinary tract, localized exclusively to nerve fibres. No immunoreactive neuronal cell bodies were observed in any of the tissues. Pituitary adenylate cyclase activating peptide was shown to be located in varicose nerve fibres associated with blood vessels and smooth muscle. The majority of pituitary adenylate cyclase activating peptide-positive nerve fibres and bundles were, however, present in subepithelial plexuses from which delicate varicose nerve fibres entered the urothelium. Double immunostaining for pituitary adenylate cyclase activating peptide and a marker for sensory neurons, calcitonin-gene related peptide, disclosed that the two peptides were almost completely co-localized while the co-existence between pituitary adenylate cyclase activating peptide and the structurally related peptide vasoactive intestinal polypeptide, was scarce. Neonatal capsaicin-treatment caused a marked reduction in the concentration of immunoreactive pituitary adenylate cyclase activating peptide in all regions of the rat urinary tract, being most prominent in the ureter. By immunohistochemistry it was shown that the sensory neurotoxin caused a reduction in the number and intensity of pituitary adenylate cyclase activating peptide-immunoreactive nerve fibres in all organs of the urinary tract which was most prominent in the epithelial and subepithelial layers. Identical changes were observed for the calcitonin-gene related peptide-containing nerve fibres, while vasoactive intestinal polypeptide-positive nerve fibres were unaffected by capsaicin-treatment. In conclusion pituitary adenylate cyclase activating peptide is present in the rat urinary tract mainly in the form of pituitary adenylate cyclase activating peptide-38. Immunoreactive nerve fibres were associated with the epithelium, blood vessels and smooth musculature. Pituitary adenylate cyclase activating peptide was almost completely co-localized with calcitonin-gene related peptide and by neonatal capsaicin treatment the two peptides were identically affected. The findings suggest that pituitary adenylate cyclase activating peptide is a sensory neurotransmitter in the rat urinary tract.

Locations and molecular forms of PACAP and sites and characteristics of PACAP receptors in canine ileum

In canine ileum we investigated the distribution of pituitary adenylate cyclase-activating peptide (PACAP), using immunofluorescence and radioimmunoassay and the binding of 125I-PACAP-27 to membranes. Nerve profiles immunoreactive to PACAP-27, and often to vasoactive intestinal polypeptide (VIP) as well, were found in all plexi, but PACAP was present in approximately 100-fold lesser amounts than VIP. High-performance liquid chromatography analysis of deep muscular plexus (DMP) synaptosomes suggested the presence of PACAP-38, PACAP-27, and a third unidentified molecular form. High- and low-affinity 125I-PACAP-27 binding sites were found in DMP synaptosomes and circular smooth muscle (CM) plasma membranes. In competition studies with DMP membranes, high (H)- and low (L)-affinity dissociation constants (Kd) and maximal binding capacities (Bmax) were as follows: KdH = 66.9 pM, BmaxH = 101 fmol/mg; KdL = 2.18 nM, BmaxL = 580 fmol/mg protein. The binding of 125I-PACAP-27 was fast. Dissociation was slow and incomplete in the presence of unlabeled PACAP-27 but accelerated by pretreatment with guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S). GTP gamma S or cholera toxin treatment eliminated high-affinity binding in both membranes. VIP had approximately 100-fold lower affinity than PACAP-27 in both membranes. Cross-linking studies identified an approximately 70-kDa PACAP receptor in each membrane. Thus PACAP coexists with VIP in ileal enteric nerves and acts on PACAP-preferring, possibly Gs-coupled, receptors in DMP synaptosomes and CM membranes.

Specific antibody recognition of rat pituitary adenylate cyclase activating polypeptide receptors

Pituitary adenylate cyclase activating polypeptide (PACAP) is a new member of the secretin/VIP family of peptides. The specific receptor for PACAP has been cloned in rat, human, and bovine tissues. The distribution of the transcripts of PACAP receptor genes has been studied in various tissues using in situ hybridization. However, the unavailability of a specific antibody against the PACAP receptor has hampered further study of the expression of receptor proteins. In the present study, rabbit antisera were generated against a synthetic 25-residue peptide corresponding to the C-terminal intracellular domain of the rat PACAP receptor. To validate the specificity of the antisera, CHO cells and cells stably transfected with rat PACAP receptor cDNA were prepared. Using one of these antisera, the membrane and soluble fractions of the transformants were examined by Western blot analysis. Three bands were observed in subcellular fractions from the transfected CHO cells, but no bands were found in similar preparations from the nontransfected cells. A distinct 57-kDa band, which corresponds to the size of cloned rat PACAP receptor, was detected. In addition, a less intense band, larger than 57 kDa, and a very weakly stained band, smaller than 57 kDa, were demonstrated. All of these bands disappeared or were considerably diminished when the antiserum was preabsorbed with the synthetic immunogen peptide. This suggests that these bands are PACAP receptor-related proteins. The membranes from the transfected CHO cells bound to [125I]PACAP27. The size of the ligand/protein crosslinked product approximated 60 kDa, corresponding to the combined size of the PACAP receptor and PACAP27. No additional bands were observed, indicating that the immunopositive proteins larger or smaller than 57 kDa do not bind to the ligand and are not functional. Unlabeled PACAP27 and PACAP38, but not VIP, displaced the binding, suggesting that the receptors expressed in CHO cells are specific for PACAP. Solubilized membrane fractions prepared from rat brains were used for an immunoprecipitation study with [125I]PACAP27 and [125I]VIP. The PACAP receptor antiserum recognized [125I]PACAP-, but not [125I]VIP-bound proteins in the solubilized brain membrane fractions. Immunohistochemistry using this antiserum showed a distribution of PACAP receptor-like immunoreactivities similar to the distribution of the mRNA of PACAP receptor in the rat brain. Thus, the PACAP receptor antiserum is sufficiently specific to be used as a tool for studying the expression of PACAP receptors and related proteins.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP-27, but not PACAP-38) degradation by the neutral endopeptidase EC 3.4.24.11

VIP (vasoactive intestinal polypeptide) and PACAP (pituitary adenylate cyclase-activating polypeptide), which are potent relaxing agents in the airways, were submitted to in vitro degradation by the neutral endopeptidase EC 3.4.24.11 (NEP), one of the most active peptidase in the lung, to test their relative resistance to proteolysis. Both VIP and PACAP(1-27) were cleaved by NEP, but PACAP(1-38) was not. The main fragments produced were VIP(1-22) and VIP(1-25), and PACAP(1-22) and PACAP(1-25), respectively. The degradation of VIP(1-27), PACAP(6-27), and PACAP(13-27) was also hindered by extending their C-terminal ends with the (28-38) sequence of PACAP(1-38). The sensitivity to enzyme degradation was gradually reduced when the C-terminal extension was increased from PACAP(1-27) to PACAP(1-29), PACAP(1-32) and PACAP(1-38). The biological activities of the degradation products were evaluated on the three classes of PACAP/VIP receptors, with VIP(1-25) and PACAP(1-25) retaining an important part of their activities on the VIP1 receptor. Thus, the degradation of VIP and PACAP(1-27) by the neutral endopeptidase 24.11 might produce a VIP1 receptor-selective active metabolite, provided that very high VIP or PACAP(1-27) concentrations are achieved in the receptor vicinity.

Expression of pituitary adenylate cyclase-activating polypeptide (PACAP) in the mesencephalic trigeminal nucleus of the rat after transsection of the masseteric nerve

Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the VIP (vasoactive intestinal polypeptide) family of peptides, has been demonstrated in neurons of the sensory system. PACAP expression of these neurons is sensitive to nerve damages such as nerve crush or axotomy. In the present study, PACAP expression in the mesencephalic trigeminal nucleus of the rat was examined after transsection of the main trunk of the masseteric nerve. The primary sensory neurons of the nucleus are considered to have purely proprioceptive functions. By quantitative in situ hybridization using a PACAP [35S]cRNA probe, an increase in PACAP mRNA was observed on the side ipsilateral to transsection already after 3 h and the expression reached a peak 24 h after surgery after which the levels gradually decreased during the next 14 days. A low and constant expression of PACAP mRNA could be seen on the side contralateral to transsection. PACAP immunoreactivity was demonstrated on the ipsilateral side after 18 h, using a specific monoclonal PACAP antibody. Co-existence of PACAP with NPY and galanin was demonstrated 7 days after transsection. Analysis of the masseteric nerve by radioimmunoassay on transsected and normal nerve stumps revealed an increase of PACAP-38 immunoreactivity in the nerve proximal to the transsection compared to the normal side (15.3 vs. 6.1 pmol/g wt). The results suggest that PACAP has a role in the early phase of adaptation to nerve injury in the proprioceptive neurons.

Comparative histology of pulmonary neuroendocrine cell system in mammalian lungs

It is increasingly recognized that neuroepithelial endocrine cells and organoid clusters of these cells termed neuroepithelial bodies are widely distributed in the respiratory tract of vertebrates. This review focuses on the neuroepithelial endocrine system in the airway epithelium of mammals according to observations made in a wide range of species, as it appears in light and electron microscopy by means of various visualization techniques under normal and experimental conditions. Because there are similarities but also marked differences between species, wherever possible studies in human airways are emphasized. Conventional histochemical and ultrastructural studies including microspectrofluorimetry have demonstrated the amine-handling properties and the presence of neurosecretory granules in neuroendocrine cells of the epithelium of all mammals studies so far. The neuroepithelial bodies are innervated by morphological afferent- and efferentlike synaptic specializations. These, together with the presence of reciprocal synapses, emphasize that these cells may be involved in dual functions of chemoreception and secretion. Light and electron microscopic immunohistochemistry has demonstrated that neuroepithelial endocrine cells may contain various biogenic agents, suggesting that the neuroendocrine system is highly heterogeneous. Neural elements may interact in a complex manner, and the activation of certain neural pathways may control the release of biogenic substances to influence physiological airway functions. They may be particularly relevant in pulmonary diseases. Consequently, the function of this system is complex and it is highly probable that many of its aspects are still not elucidated.

Local effect of PACAP and VIP on testicular function in immature and adult rats

PACAP, VIP, anti-PACAP and anti-VIP antisera were injected intratesticularly. In 9-day-old hemicastrated rats PACAP or VIP decreased basal testosterone secretion. In 22-day-old hemicastrates VIP but not PACAP reduced compensatory testicular hypertrophy, however, neither PACAP nor VIP altered steroidogenesis. Anti-VIP antiserum to this age group increased testosterone production and enhanced compensatory testicular hypertrophy. In adult hemicastrates neither the peptides nor the antisera influenced steroidogenesis. Neither in immatures nor in adults treatment of both testes with PACAP or VIP had any effect. Data indicate that both PACAP and VIP might exert a local action on testicular steroidogenesis, on compensatory testicular hypertrophy, and these effects are age-dependent.