Pituitary Adenylate Cyclase-activating Peptide Peptides Research Articles

VIP and PACAP receptors in GtoPdb v.2023.1

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Vasoactive Intestinal Peptide Receptors [65, 66]) are activated by the endogenous peptides VIP, PACAP-38, PACAP-27, peptide histidine isoleucineamide (PHI), peptide histidine methionineamide (PHM) and peptide histidine valine (PHV). VPAC1 and VPAC2 receptors display comparable affinity for the PACAP peptides, PACAP-27 and PACAP-38, and VIP, whereas PACAP-27 and PACAP-38 are >100 fold more potent than VIP as agonists of most isoforms of the PAC1 receptor. However, one splice variant of the human PAC1 receptor has been reported to respond to PACAP-38, PACAP-27 and VIP with comparable affinity [30]. PG 99-465 [117] has been used as a selective VPAC2 receptor antagonist in a number of physiological studies, but has been reported to have significant activity at VPAC1 and PAC1 receptors [36]. The selective PAC1 receptor agonist maxadilan, was extracted from the salivary glands of sand flies (Lutzomyia longipalpis) and has no sequence homology to VIP or the PACAP peptides [118]. Two deletion variants of maxadilan, M65 [183] and Max.d.4 [119] have been reported to be PAC1 receptor antagonists, but these peptides have not been extensively characterised.

Differences in pituitary adenylate cyclase-activating peptide and calcitonin gene-related peptide release in the trigeminovascular system.

Several neurotransmitters are expressed in the neurons of the trigeminal ganglion. One such signalling molecule is the pituitary adenylate cyclase-activating peptide (PACAP). PACAP signalling has been suggested to have a possible role in the pathophysiology of primary headaches. The present study was designed to investigate the relationship between PACAP and calcitonin gene-related peptide, currently the two most relevant migraine peptides. In the current study, we used ELISA to investigate PACAP and calcitonin gene-related peptide release in response to 60 mM K+ or capsaicin using a rat hemi-skull model. We combined this analysis with qPCR and immunohistochemistry to study the expression of PACAP and calcitonin gene-related peptide receptors and ligands. Calcitonin gene-related peptide (CGRP) is released from the trigeminal ganglion and dura mater. In contrast, PACAP is only released from the trigeminal ganglion. We observed a weak correlation between the stimulated release of the two neuropeptides. PACAP-38 immunoreactivity was expressed alone and in a subpopulation of neurons in the trigeminal ganglion that also store calcitonin gene-related peptide. The receptor subtype PAC1 was mainly expressed in the satellite glial cells (SGCs), which envelop the neurons in the trigeminal ganglion, in some neuronal processes, inside the Aδ-fibres and in the outermost layer of the myelin sheath that envelopes the Aδ-fibres. Unlike CGRP, PACAP is only released within the trigeminal ganglion. This raises the question of whether a migraine therapy aimed at preventing peripheral PACAP signalling would be as successful as the CGRP signalling targeted treatments.

Drosophila Middle-Term Memory: Amnesiac is Required for PKA Activation in the Mushroom Bodies, a Function Modulated by Neprilysin 1.

In Drosophila, the mushroom bodies (MB) constitute the central brain structure for olfactory associative memory. As in mammals, the cAMP/PKA pathway plays a key role in memory formation. In the MB, Rutabaga (Rut) adenylate cyclase acts as a coincidence detector during associative conditioning to integrate calcium influx resulting from acetylcholine stimulation and G-protein activation resulting from dopaminergic stimulation. Amnesiac encodes a secreted neuropeptide required in the MB for two phases of aversive olfactory memory. Previous sequence analysis has revealed strong homology with the mammalian pituitary adenylate cyclase-activating peptide (PACAP). Here, we examined whether amnesiac is involved in cAMP/PKA dynamics in response to dopamine and acetylcholine co-stimulation in living flies. Experiments were conducted with both sexes, or with either sex. Our data show that amnesiac is necessary for the PKA activation process that results from coincidence detection in the MB. Since PACAP peptide is cleaved by the human membrane neprilysin hNEP, we searched for an interaction between Amnesiac and Neprilysin 1 (Nep1), a fly neprilysin involved in memory. We show that when Nep1 expression is acutely knocked down in adult MB, memory deficits displayed by amn hypomorphic mutants are rescued. Consistently, Nep1 inhibition also restores normal PKA activation in amn mutant flies. Taken together, the results suggest that Nep1 targets Amnesiac degradation to terminate its signaling function. Our work thus highlights a key role for Amnesiac in establishing within the MB the PKA dynamics that sustain middle-term memory (MTM) formation, a function modulated by Nep1.SIGNIFICANCE STATEMENT The Drosophila amnesiac gene encodes a secreted neuropeptide whose expression is required for specific memory phases in the mushroom bodies (MB), the olfactory memory center. Here, we show that Amnesiac is required for PKA activation resulting from coincidence detection, a mechanism by which the MB integrate two spatially distinct stimuli to encode associative memory. Furthermore, our results uncover a functional relationship between Amnesiac and Neprilysin 1 (Nep1), a membrane peptidase involved in memory and expressed in the MB. These results suggest that Nep1 modulates Amnesiac levels. We propose that on conditioning, Amnesiac release from the MB allows, via an autocrine process, the sustaining of PKA activation-mediating memory, which subsequently is inactivated by Nep1 degradation.

Pharmacological Characterisation of PACAP‐responsive Receptors Reveals Signalling Bias and Probe‐dependent Antagonism

Pituitary adenylate cyclase‐activating peptide (PACAP) is a neuropeptide which exists in two biologically active forms; PACAP‐27 and PACAP‐38. PACAP is widely expressed in the brain and periphery where it is involved in many physiological processes including pain, inflammation, stress and anxiety. PACAP potently activates three different G protein‐coupled receptors (GPCRs); the PAC1 receptor, the VPAC1 receptor and VPAC2 receptor. The VPAC receptors are co‐receptors for PACAP and vasoactive intestinal peptide (VIP). The PAC1 receptor has several known splice variants in the N‐terminal domain, which include the PAC1n receptor (full N‐terminus) and the PAC1s receptor (21 amino acid N‐terminal deletion). To develop therapeutics targeting the PACAP system, it is essential to understand how these receptors signal and how this signalling is inhibited. Here we pharmacologically characterised the signalling capabilities of PACAP‐responsive receptors and how these responses were blocked by antagonists.The pharmacology of the human PAC1n, PAC1s, VPAC1, VPAC2 receptors were examined in transfected Cos7 cells. Using concentration‐response curves, the ability of PACAP and related peptides to stimulate cAMP, IP1, pAkt, pERK and pCREB responses were measured. Signalling bias was then quantified. The ability of multiple antagonists to block PACAP‐38, PACAP‐27 or VIP‐induced cAMP responses at PACAP‐responsive receptors was then determined.PACAP‐responsive receptors stimulated activation of all signalling molecules measured. However, only limited signalling bias was observed. For example, VIP was 4‐fold biased towards cAMP production over IP1 production at the PAC1n receptor. Interestingly, the PAC1n and PAC1s receptors displayed distinct pharmacology. At the PAC1s receptor, VIP was found to be 20‐fold more potent than at the PAC1n receptor. Probe‐ or agonist‐dependent antagonism was observed at the PAC1n and PAC1s receptors. Both VIP and PACAP‐27 were more potently antagonised than PACAP‐38 by the antagonists PACAP6–38 and M65.The distinct pharmacological profile displayed by the PAC1s receptor, suggests that it can act as a dual receptor for VIP and PACAP under specific conditions. Furthermore, differences in antagonist pharmacology at PACAP‐responsive receptors suggests the effectiveness of blocking a signalling pathway can be influenced by which endogenous agonist is present. These effects have potential implications for the development and effectiveness of drugs targeting the PAC1 receptor.Support or Funding InformationThis research is supported by grants from the Royal Society of New Zealand Marsden Fund (RSNZ) and the Health Research Council of New Zealand (HRC).

VIP and PACAP receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Vasoactive Intestinal Peptide Receptors [64, 65]) are activated by the endogenous peptides VIP, PACAP-38, PACAP-27, peptide histidine isoleucineamide (PHI), peptide histidine methionineamide (PHM) and peptide histidine valine (PHV). VPAC1 and VPAC2 receptors display comparable affinity for the PACAP peptides, PACAP-27 and PACAP-38, and VIP, whereas PACAP-27 and PACAP-38 are >100 fold more potent than VIP as agonists of most isoforms of the PAC1 receptor. However, one splice variant of the human PAC1 receptor has been reported to respond to PACAP-38, PACAP-27 and VIP with comparable affinity [29]. PG 99-465 [115] has been used as a selective VPAC2 receptor antagonist in a number of physiological studies, but has been reported to have significant activity at VPAC1 and PAC1 receptors [35]. The selective PAC1 receptor agonist maxadilan, was extracted from the salivary glands of sand flies (Lutzomyia longipalpis) and has no sequence homology to VIP or the PACAP peptides [116]. Two deletion variants of maxadilan, M65 [180] and Max.d.4 [117] have been reported to be PAC1 receptor antagonists, but these peptides have not been extensively characterised.

Stress-specific changes of galanin and PACAP expression in the rat hypothalamus and adrenal gland

Galanin and pituitary adenylate cyclase-activating peptide (PACAP) are involved in the stress response, and both produce multiple effects in the central and peripheral nervous systems. In rodents, galanin brain expression is altered by different stressors, while PACAP has a critical role in the circuits mediating the stress-response. The aim of this study was to investigate whether acute and/or repeated immobilization (IMO) and restraint (R) differently affect galanin and PACAP expression in the rat hypothalamus and adrenal gland. Relative expression of mRNAs was examined by qPCR and relative changes in the protein content were analyzed using Western blotting. The distribution of galanin and PACAP peptides in the hypothalamus was analyzed by immunofluorescence. Relative hypothalamic expression of both galanin and PACAP mRNAs was increased only after repeated restraint. Hypothalamic galanin protein levels were increased after all applied stressors, whereas there were no changes in the PACAP content. In the adrenal glands, galanin and PACAP mRNAs were elevated only after acute IMO, whereas the protein levels were not changed, regardless of the applied stressor or its duration. Immunofluorescence staining demonstrated the presence of galanin in the paraventricular nuclei (PVN) of the hypothalamus in all groups. Galanin immunoreactivity was stronger in the PVN of all stressed groups in comparison to the control. We concluded that the patterns of transcriptional activation and translational control of galanin and PACAP in the examined tissues depended on the type (IMO vs. R) and duration (acute vs. repeated) of the applied stressor.

Expression of pituitary adenylate cyclase-activating peptide, vasoactive intestinal peptide and their receptors in diabetic rat retinas

Pituitary adenylate cyclase-activating peptide (PACAP), vasoactive intestinal peptide (VIP) and their related receptors have already been described in the retina of different mammalian species during development. Based on relative affinity studies, at least three different binding sites have been identified for PACAP and VIP: the PACAPpreferring PAC1 receptors and, VPAC1 and VPAC2 receptors which bind with equal affinity both PACAP and VIP. However, peptides and receptors expression in early diabetic retinopathy remains unknown. In the present study we investigated PACAP, VIP and relative receptors expression and distribution in the retina of streptozotocin (STZ)induced diabetic rats. Diabetes was induced in Wistar rats by a single STZ intraperitoneal injection. The expression of PACAP, VIP and receptors in healthy and early diabetic retinas were assayed both after 1 and 3 weeks by quantitative real-time PCR, Western blot and immunohistochemical analyses. VPAC1 and VPAC2 receptors, as well as PACAP and VIP peptides mRNA levels were transiently induced by STZ-treatment within 1 week. After 3 weeks, PAC1, VPAC receptors and their related peptides expression levels were remarkably reduced in diabetic as compared to healthy rat retinas. These findings were confirmed at the protein level by immunoblot. Interestingly, immunohistochemical analyses revealed some peculiar changes in PACAP, VIP and receptors distribution between the two animal groups. In fact, after 1 week treatment, PACAP was more expressed in the retinal pigmented epithelium (RPE) and in the inner segment of diabetic rats. Similarly, VIP reactivity was remarkably increased in the RPE, but also in the inner plexiform layer of STZ-treated rats. No apparent changes were observed in PAC1 immunoreactivity between healthy and diabetic rats, although the RPE was slightly less reactive in the latter group. VPAC2 receptors seemed to be more expressed in the inner nuclear layer but less evident in the outer nuclear layer of STZ-treated rats. VPAC1 receptor retinal distribution was not affected by STZ-treatment. These differences were no longer observable 3 weeks after the STZ injection, although an overall reduction of both peptides and receptors expression occurred. In conclusion, this study provides evidence of an involvement of both PACAP and VIP peptides in early diabetic retinopathy. Furthermore, the overall downregulation of both peptides/receptors expression in retinas of STZ-treated rats after 3 weeks suggests that some deregulatory mechanisms might be activated in the later stages of retinal degeneration.

The effects of PACAP and related peptides on leptin, soluble leptin receptor and resistin in normal condition and LPS-induced inflammation

Leptin and resistin are adipokines considered as pro-inflammatory factors related to metabolic syndrome, inflammatory and/or autoimmune conditions. Pituitary adenylate cyclase activating peptide (PACAP) is a pleiotropic neuropeptide with anti-inflammatory properties. We investigated the influence of PACAP on the serum level of leptin, soluble leptin receptor (SLR) and resistin in ordinary and LPS-induced inflammatory conditions using PACAP38 and a series of selective agonist for each PACAP receptor types. It was found that PACAP exerted opposite effects on the leptin:SLR ratio and the serum resistin level. In ordinary condition, PACAP acted as a pro-inflammatory factor by increasing the leptin:SLR ratio and serum resistin level. But in LPS-induced acute inflammatory condition, PACAP not only antagonized the effects of LPS, but also even reversed the effects of LPS. In mice treated with LPS, co-treatment with PACAP decreased the serum leptin and resistin levels and increased the serum soluble leptin receptor level significantly. It was also found that, in ordinary condition, treatment with PAC1 agonist maxadilan induced marked increase in serum leptin, leptin:SLR ratios and resistin levels; while in LPS-induced inflammation, VPAC1 mediated much more anti-inflammatory and reversing-LPS effects of PACAP on leptin and resistin than PAC1 and VPAC2. It is concluded that different receptors mediates different effects of PACAP on leptin, SLR and resistin in non-inflammatory and LPS-induced inflammatory conditions.

PACAP modulation of the colon-inferior mesenteric ganglion reflex in the guinea pig.

We investigated the effect of pituitary adenylate cyclase activating peptide (PACAP) on the colon-inferior mesenteric ganglion (IMG) reflex loop in vitro. PACAP27 and PACAP38 applied to the IMG caused a prolonged depolarization and intense generation of fast EPSPs and action potentials in IMG neurones. Activation of PACAP-preferring receptors (PAC1-Rs) with the selective agonist maxadilan or vasoactive intestinal peptide (VIP)/PACAP (VPAC) receptors with VIP produced similar effects whereas prior incubation of the IMG with selective PAC1-R antagonists PACAP6-38 and M65 inhibited the effects of PACAP. Colonic distension evoked a slow EPSP in IMG neurones that was reduced in amplitude by prolonged superfusion of the IMG with either PACAP27, maxidilan, PACAP6-38, M65 or VIP. Activation of IMG neurones by PACAP27 or maxadilan resulted in an inhibition of ongoing spontaneous colonic contractions. PACAP-LI was detected in nerve trunks attached to the IMG and in varicosities surrounding IMG neurones. Cell bodies with PACAP-LI were present in lumbar 2-3 dorsal root ganglia and in colonic myenteric ganglia. Colonic distension evoked release of PACAP peptides in the IMG as measured by radioimmunoassay. Volume reconstructed images showed that a majority of PACAP-LI, VIP-LI and VAChT-LI nerve endings making putative synaptic contact onto IMG neurones and a majority of putative receptor sites containing PAC1-R-LI and nAChR-LI on the neurones were distributed along secondary and tertiary dendrites. These results suggest involvement of a PACAP-ergic pathway, operated through PAC1-Rs, in controlling the colon-IMG reflex.

Involvement of pituitary adenylate cyclase-activating peptide in opossum internal anal sphincter relaxation

Despite its widespread distribution and significance in the gut, the role of pituitary adenylate cyclase-activating peptide (PACAP) in internal anal sphincter (IAS) relaxation has not been examined. This study examined the role of PACAP in nonadrenergic noncholinergic (NANC) nerve-mediated relaxation of IAS smooth muscle. Circular smooth muscle strips from the opossum IAS were prepared for measurement of isometric tension. The influence of PACAP and vasoactive intestinal peptide (VIP) antagonists and tachyphylaxis on the neurally mediated IAS relaxation was examined either separately or in combination. The release of these neuropeptides in response to NANC nerve stimulation before and after the nitric oxide (NO) synthase inhibitor Nomega-nitro-L-arginine and NO was also investigated. Both PACAP and VIP antagonists caused significant attenuation of IAS relaxation by NANC nerve stimulation. The combination of the antagonists, however, did not have an additive effect on IAS relaxation. VIP tachyphylaxis caused significant suppression of IAS relaxation by NANC nerve stimulation. PACAP and VIP were found to be released by NANC nerve stimulation and exogenous NO. The data suggest the involvement of PACAP in IAS relaxation primarily by the activation of PACAP1/VIP receptor and lack of its independent role in the relaxation. Furthermore, NO may regulate the presynaptic release of PACAP and VIP.

Capsaicin-evoked release of pituitary adenylate cyclase activating peptide (PACAP) and calcitonin gene-related peptide (CGRP) from rat spinal cord in vivo

Capsaicin-evoked release of pituitary adenylate cyclase activating peptide (PACAP)-like immunoreactivity (LI) from rat spinal cord was examined in vivo. In anaesthetized rats, a catheter was inserted through the atlanto–occipital membrane into the subarachnoid space at the level of the sacral spinal cord for infusion of artificial cerebrospinal fluid. Another catheter was placed in the cisternal opening for outflow. Blood pressure was monitored and kept stable during the experiment. Perfusion samples were analyzed for PACAP and calcitonin gene-related peptide (CGRP) by radioimmunoassay. The addition of capsaicin (10 μM) to the perfusate elevated the concentrations of PACAP-27-LI in the artificial cerebrospinal fluid by 177%, PACAP-38-LI by 93% and CGRP-LI by 692%. In view of the presence of PACAP-immunoreactive nerve fibres in the superficial layers of the dorsal horn and the expression of PACAP in the small sized neurons in the dorsal root ganglia, the findings suggest that PACAP is released into the artificial cerebrospinal fluid from C-fibres in the spinal cord. PACAP conceivably plays a modulating role in nociception

PACAP immunoreactivity in the rat superior cervical ganglion in comparison to VIP.

The presence and regulation of pituitary adenylate cyclase activating peptide (PACAP) was investigated in the adult rat superior cervical ganglion. Double-labelling immunofluorescence using specific antibodies against PACAP and vasoactive intestinal peptide (VIP) revealed a dense innervation of postganglionic sympathetic neurones by PACAP-immunoreactive but VIP-negative nerve endings that mainly were of preganglionic origin since they disappeared after transection of the cervical sympathetic trunk. Since PACAP regulates transmitter synthesis and release in sympathetic neurones in vitro, this finding provides a morphological correlate for modulatory effects of PACAP in vivo. Few neurones contained PACAP under normal conditions. However, the number of PACAP-positive neurones increased in response to axotomy of the postganglionic nerves. Many of the newly PACAP-positive neurones also contained VIP, suggesting that both peptides are regulated by similar mechanisms.

Expression of pituitary adenylate cyclase activating peptide (PACAP) and PACAP type I receptors in the rat adrenal medulla

Pituitary adenylate cyclase activating polypeptide (PACAP) which belongs to the vasoactive intestinal polypeptide family of regulatory peptides, occurs in two variants, PACAP-27 and PACAP-38, and is thought to be an important messenger in both the central and peripheral nervous system. Three cloned G-protein coupled 7 transmembrane spanning receptors bind PACAP with high affinity, one reacting only weakly with VIP (PACAP type I receptor) the other two binding vasoactive intestinal peptide (VIP) with equally high affinity (VIP type I and II receptors). The PACAP type I receptor displays high affinity for both variants of PACAP. In this study, we have investigated the distribution of PACAP and the PACAP type I receptor in the adrenal medulla of newborn and adult rat. Immunocytochemistry revealed, in the adult rat, a dense network of PACAP-immunoreactive nerve fibers terminating on chromaffin cells. Such fibers were few and weakly immunoreactive in the newborn rat. PACAP-immunoreactive medullary cells could not be detected in the adult rat, whereas in the newborn, occasional cells were seen. By in situ-hybridization we detected PACAP type I receptor mRNA in a majority of the adrenal medullary cells of both newborn and adult rat. Receptor autoradiography using 125I-PACAP-27 as ligand revealed binding-sites with a localization virtually identical to the in situ hybridization signal indicating a functional expression of high-affinity type 1 PACAP receptors in the adrenal medulla. Additionally, in the adult rat, single or clustered large cells, presumably ganglion cells, contained an even higher abundance of PACAP receptor mRNA as well as binding sites than the surrounding chromaffin cells. Our observations on the distribution of PACAP peptide and PACAP receptors in the adrenal medulla suggest that both chromaffin cells and ganglion cells are PACAP targets. The data thus strengthen earlier observations indicating an important regulatory role of PACAP in catecholamine biosynthesis and release. The presence of both ligand and receptors in newborn rats may indicate a role for PACAP in the development of the adrenal medulla.

PACAP acts through VIP type 2 receptors in the rat testis

Pituitary adenylate cyclase-activating peptide (PACAP) is present and synthesized in the testis in large amounts. Messenger RNA encoding the peptide is expressed in a stage specific manner in the developing germ cells. PACAP regulates a variety of physiological actions, among them, paracrine modulation of spermatogenesis. The PACAP peptides are potential ligands of at least three receptor types, the type I PACAP receptor, VIP1 and VIP2 receptors. Although PACAP27 binding sites have found in the testis, the receptor at which it acts has not been identified. We used in situ hybridization with riboprobes to identify the PACAP binding receptor present in the testis. Neither type I PACAP receptor, nor VIP1 receptor mRNA was present within the germ cells. Using the VIP2 receptor probe there was strong labelling within some cross sections of the seminiferous tubuli, while others were not labelled. The in situ results were also confirmed using reverse-transcription PCR (RT-PCR). Our data suggest that PACAP mediates its possible paracrine effect in the testis through the VIP2 receptor.

Presence and effects of pituitary adenylate cyclase activating peptide in the submandibular gland of the ferret

Pituitary adenylate cyclase activating peptide (PACAP), a recently described vasoactive intestinal peptide-like neuropeptide, was found to be present in neurons in the submandibular gland of the ferret, where PACAP-immunoreactive nerve fibers were distributed around blood vessels, acini and ducts. Most of the PACAP-immunoreactive fibres were distinct from those storing vasoactive intestinal peptide. PACAP occurs in tissues as PACAP1-38 and PACAP1-27. PACAP1-38 and PACAP1-27 but not PACAP16-38 displayed biological activity with about the same potency. They exerted vasodilator effects on the submandibular vasculature, which resulted in a greater fall in vascular resistance than an equimolar dose of vasoactive intestinal peptide. The vasodilator response was independent of muscarinic receptor activation. Neither vasoactive intestinal peptide nor PACAP alone evoked any flow of saliva. However, both vasoactive intestinal peptide and PACAP enhanced the fluid response to acetylcholine, and the flow of saliva as well as the output of protein in response to parasympathetic nerve stimulation, vasoactive intestinal peptide being more potent than PACAP. In vitro, protein was released from submandibular gland tissue in response to both vasoactive intestinal peptide and PACAP, vasoactive intestinal peptide being more potent than PACAP. PACAP (and vasoactive intestinal peptide) exerted its in vitro effect following adrenoceptor and muscarinic blockade and following degeneration of sympathetic nerves. Sympathetic denervation combined with parasympathetic preganglionic denervation resulted in supersensitivity to both vasoactive intestinal peptide and PACAP. The fact that PACAP and vasoactive intestinal peptide occur in different nerve fibre populations suggests different roles for the two peptides in the submandibular gland.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of VIP, PACAP and related peptides in normal and leukemic human monocytes and macrophages

The activation of the cAMP signaling pathway by vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP) and related peptides was studied (i) in normal peripheral human monocytes and THP-1 leukemic human monocytes, (ii) in their derived macrophage counterparts respectively obtained after spontaneous differentiation or retinoic acid (RA) treatment, and (iii) in human bronchoalveolar macrophages. In THP-1 monocytes, PACAP increased basal adenylate cyclase activity 5.3-fold, with an affinity 50-times greater than that of VIP or helodermin ( K a = 3.2 × 10 −11 M VIP), whereas in normal peripheral monocytes, PACAP and VIP exhibited similar affinities and only increased eAMP generation 2-fold (EC 50 = 10 −9 M). Spontaneous and RA-induced differentiation into normal and leukemic macrophages induced a progressive loss of cAMP production and regulation of superoxide anion production by VIP and related peptides. The neoplastic transformation in THP-1 monocytes and the deficiencies in the cAMP cascade observed during the terminal differentiation of normal and leukemic human macrophages may relate to a differential genetic expression of the VIP/PACAP receptor subtypes, and alterations in the functional activity of the stimulatory and inhibitory G s/G i subunits of adenylate cyclase.

Pituitary adenylate cyclase-activating peptide is a potent modulator of human colonic motility.

Pituitary adenylate cyclase-activating peptide (PACAP) represents a novel brain-gut peptide with high sequence homology to vasoactive intestinal polypeptide (VIP). Since PACAP has been identified in the human gut, the effect of the two molecular forms PACAP-(1-38) and PACAP-(1-27), the hybrid PACAP-(1-23)VIP-(24-28), and VIP on the contractility of the longitudinal muscle of human sigmoid colon was tested in vitro. All peptides inhibited the spontaneous phasic contractions and relaxed concentration-dependently carbachol-precontracted preparations. The effects of the peptides remained unaffected by tetrodotoxin, by inhibition of phosphodiesterase activity, and by inhibition of nitric oxide synthesis. Apamin reduced only the effects of the PACAP peptides, whereas tetraethylammonium blocked only the effect of VIP. In conclusion, PACAP peptides and VIP mediate their relaxant effects via activation of specific PACAP and VIP receptors coupled to different potassium channels.