Newly-identified receptors for peptide histidine-isoleucine and GHRH-like peptide in zebrafish help to elucidate the mammalian secretin superfamily

A group of ten hormones in humans are structurally related and known as the secretin superfamily. These hormones bind to G-protein-coupled receptors that activate the cAMP pathway and are clustered as the secretin or B family. We used an evolutionary approach with zebrafish as a model to understand why some of these hormones, such as peptide histidine-methionine (PHM) and pituitary adenylate cyclase-activating polypeptide (PACAP)-related peptide (PRP) in humans lack a receptor. We used molecular techniques to clone two full-length receptor cDNAs in zebrafish, which were analyzed for amino acid sequence and ligand-binding motifs, phylogenetic position, synteny, tissue expression, functional response, and signaling pathway. Evidence is provided that the two cDNAs encoded the peptide histidine-isoleucine (PHI) receptor and PRP receptor, which is known as GHRH-like peptide (GHRH-LP) receptor in non-mammals. Further, we cloned a zebrafish cDNA encoding the peptides PHI and vasoactive intestinal peptide (VIP). The PHIR had been previously labeled as one type of a VIP-PACAP (VPAC2R) shared receptor based only on sequence data. The PHIR cDNA, transfected into COS7 cells, responded to zebrafish PHI in a sensitive and dose-dependent manner (EC(50)=1.8x10(-9) M) but not to PACAP and VIP. The GHRH-LP receptor responded to both zebrafish GHRH-LP1 and GHRH with a 3.5-fold greater response to the former. For comparison, two zebrafish receptors (PAC1R and VPAC1R) and two human receptors (VPAC2R and GHRHR) were tested with human and/or zebrafish peptides. Unexpectedly, zebrafish VIP activated its PAC1R suggesting that in evolution, PAC1R is not always a specific receptor for PACAP. We conclude that zebrafish, like goldfish, have a specific receptor for PHI and GHRH-LP. Our evidence that zebrafish PHI is more potent than human PHM in activating the human VPAC2R (EC(50)=7.4x10(-9) M) supports our suggestion that the VPAC2R and PHIR shared a common ancestral receptor.

Glucagon-related peptides in the mouse retina and the effects of deprivation of form vision

BACKGROUND

In chickens, retinal glucagon amacrine cells play an important role in emmetropization, since they express the transcription factor ZENK (also known as NGFI-A, zif268, tis8, cef5, Krox24) in correlation with the sign of imposed image defocus. Pharmacological studies have shown that glucagon can act as a stop signal for axial eye growth, making it a promising target for pharmacological intervention of myopia. Unfortunately, in mammalian retina, glucagon itself has not yet been detected by immunohistochemical staining. To learn more about its possible role in emmetropization in mammals, we studied the expression of different members of the glucagon hormone family in mouse retina, and whether their abundance is regulated by visual experience.

METHODS

Black wildtype C57BL/6 mice, raised under a 12/12 h light/dark cycle, were studied at postnatal ages between P29 and P40. Frosted hemispherical thin plastic shells (diffusers) were placed in front of the right eyes to impose visual conditions that are known to induce myopia. The left eyes remained uncovered and served as controls. Transversal retinal cryostat sections were single- or double-labeled by indirect immunofluorescence for early growth response protein 1 (Egr-1, the mammalian ortholog of ZENK), glucagon, glucagon-like peptide-2 (GLP-2), glucose-dependent insulinotropic polypeptide (GIP), peptide histidine isoleucine (PHI), growth hormone-releasing hormone (GHRH), pituitary adenylate cyclase-activating polypeptide (PACAP), secretin, and vasoactive intestinal polypeptide (VIP). In total, retinas of 45 mice were studied, 28 treated with diffusers, and 17 serving as controls.

RESULTS

Glucagon itself was not detected in mouse retina. VIP, PHI, PACAP and GIP were localized. VIP was co-localized with PHI and Egr-1, which itself was strongly regulated by retinal illumination. Diffusers, applied for various durations (1, 2, 6, and 24 h) had no effect on the expression of VIP, PHI, PACAP, and GIP, at least at the protein level. Similarly, even if the analysis was confined to cells that also expressed Egr-1, no difference was found between VIP expression in eyes with diffusers and in eyes with normal vision.

CONCLUSIONS

Several members of the glucagon super family are expressed in mouse retina (although not glucagon itself), but their expression pattern does not seem to be regulated by visual experience.

Unconventional binding sites and receptors for VIP and related peptides PACAP and PHI/PHM: an update

The 28-amino-acid neuropeptide VIP and related peptides PACAP and PHI/PHM modulate virtually all of the vital functions in the body. These peptides are also commonly recognized as major regulators of cell growth and differentiation. Through their trophic and cytoprotective functions, they appear to play major roles in embryonic development, neurogenesis and the progression of a number of cancer types. These peptides bind to three well-characterized subtypes of G-protein coupled receptors: VPAC1 and VPAC2 share a common high affinity in the nanomolar range for VIP and PACAP; a third receptor type, PAC1, has been characterized for its high affinity for PACAP but its low affinity for VIP. Complex effects and pharmacological behaviors of these peptides suggest that multiple subtypes of binding sites may cooperate to mediate their function in target cells and tissues. In this complex response, some of these binding sites correspond to the definition of the conventional receptors cited above, while others display unexpected pharmacological and functional properties. Here we present potential clues that may lead investigators to further characterize the molecular nature and functions of these atypical binding species.

Expression and GTP sensitivity of peptide histidine isoleucine high-affinity-binding sites in rat

High-affinity-binding sites for the vasoactive intestinal peptide (VIP) analogs peptide histidine/isoleucine-amide (PHI)/carboxyterminal methionine instead of isoleucine (PHM) are expressed in numerous tissues in the body but the nature of their receptors remains to be elucidated. The data presented indicate that PHI discriminated a high-affinity guanosine 5'-triphosphate (GTP)-insensitive-binding subtype that represented the totality of the PHI-binding sites in newborn rat tissues but was differentially expressed in adult animals. The GTP-insensitive PHI/PHM-binding sites were also observed in CHO cells over expressing the VPAC2 but not the VPAC1 VIP receptor.

Roles of PACAP and PHI as inhibitory neurotransmitters in the circular muscle of mouse antrum

Mediators of neurogenic responses of the gastric antrum were studied in wild-type and pituitary adenylate cyclase-activating polypeptide (PACAP) -knockout (KO) mice. Electrical field stimulation (EFS) to the circular muscle strips of the wild-type mouse antrum induced a triphasic response; rapid transient relaxation and contraction, and sustained relaxation that was prolonged for an extended period after the end of EFS. The transient relaxation and contraction were completely inhibited by L-nitroarginine and atropine, respectively. The sustained relaxation was significantly inhibited by a PACAP receptor antagonist, PACAP(6-38). The antral strips prepared from PACAP-KO mice unexpectedly exhibited a tri-phasic response. However, the sustained relaxation was decreased to about one-half of that observed in wild-type mice. PACAP(6-38) inhibited EFS-induced sustained relaxation (33.5% of control) in PACAP-KO mice. Anti-peptide histidine isoleucine (PHI) serum partially (the 30% inhibition) or significantly (the 60% inhibition) inhibited the sustained relaxations in the wild-type and PACAP-KO mice, respectively. The immunoreactivities to the anti-PACAP and anti-PHI serums were found in myenteric ganglia of the mouse antrum. These results suggest that nitric oxide and acetylcholine mediate the transient relaxation and contraction, respectively, and that PACAP and PHI separately mediate the sustained relaxation in the antrum of the mouse stomach.

PACAP- and PHI-mediated sustained relaxation in circular muscle of gastric fundus: findings obtained in PACAP knockout mice

Mediators of neurogenic responses of the gastric fundus were studied in wild type and pituitary adenylate cyclase activating peptide (PACAP) knockout mice. Electrical field stimulation (EFS) to the circular muscle strips of the wild type mouse fundus induced a tri-phasic response, rapid transient contraction and relaxation, and sustained relaxation that was prolonged for an extended period after the end of EFS. The transient relaxation and contraction were completely inhibited by N(G)-nitro-L-arginine and atropine, respectively. The sustained relaxation was completely inhibited by a PACAP receptors antagonist, PACAP(6-38). The strips prepared from PACAP knockout mice exhibited a large contraction without rapid relaxation and unexpectedly, a sustained relaxation. However, the sustained relaxation was decreased to about a half of that observed in wild type mice. Anti-peptide histidine isoleucine (PHI) serum abolished the sustained relaxation in the knockout mice. The serum partially inhibited the sustained relaxation in wild type mice and PACAP(6-38) abolished the relaxation that remained after the antiserum-treatment. PHI relaxed the strips prepared from wild type mice. The relaxation was completely inhibited by PACAP(6-38). It was concluded that PACAP and PHI separately mediate the sustained relaxation in the mouse gastric fundus, and that nitric oxide and ACh mediate transient relaxation and contraction, respectively.

VPAC2 receptors mediate vasoactive intestinal peptide-induced neuroprotection against neonatal excitotoxic brain lesions in mice

Prepro-vasoactive intestinal peptide (VIP) mRNA codes for two neuropeptides: VIP and peptide histidine isoleucine (PHI). Two VIP receptors, shared with a similar affinity by pituitary adenylate cyclase-activating polypeptide (PACAP), have been cloned: VPAC(1) and VPAC(2). PHI binds to these receptors with a lower affinity. VPAC receptors are classically associated with a cAMP-dependent pathway, although other pathways, including calcium mobilization and protein kinase C activation have been described. We previously showed that intracerebral administration of the glutamate agonist ibotenate to postnatal day 5 mice induces white matter lesions mimicking human periventricular leukomalacia. In this model, coinjection of VIP protects against white matter lesions. This neuroprotection is independent from cAMP and is mediated by protein kinase C. Using this model, this study aimed to determine the receptor involved in VIP-induced neuroprotection. VIP effects were mimicked with a similar potency by VPAC(2) agonists and PHI but not by VPAC(1) agonists, PACAP 27, or PACAP 38. VIP neuroprotective effects were lost in mice lacking VPAC(2) receptor. In situ hybridization confirmed the presence of VPAC(2) mRNA in the postnatal day 5 white matter. When analyzed between embryonic life and adulthood, VIP-specific binding site density peaked at postnatal day 5. These data suggest that, in this model, VIP-induced neuroprotection is mediated by VPAC(2) receptors. The pharmacology of this VPAC(2) receptor seems unconventional because 1) PACAP does not mimic VIP effects, 2) PHI acts with a comparable potency, and 3) PACAP 27 modestly inhibited the VIP-specific binding, whereas for PHI or VIP, inhibition was complete.

[Neuroprotective role of PACAP, VIP, and PHI in the central nervous system]

Pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), and peptide histidine-isoleucine (PHI) belong to a structurally related family of polypeptides present in many regions of the central and peripheral nervous system. The neuroprotective potential of PACAP, VIP, and PHI has become a matter of intensive investigations in many animal models. In vitro studies revealed that PACAP protects neurons against apoptosis occurring naturally during CNS development and apoptosis induced by a series of neurotoxins, such as ethanol, hydrogen peroxide (H2O2), prion protein, beta-amyloid, HIV envelope glycoprotein (gp120), potassium ion deficit, and high glutamate concentrations. Similarly, in vivo investigations conducted in models of ischemia and Parkinson's disease confirmed the neuroprotective properties of PACAP. It was revealed that the anti-apoptotic action of PACAP can be directly associated with the activation of signal transduction pathways preventing apoptosis in neurons or involve glial cells capable of releasing other neuroprotective factors affecting neurons. In contrast to PACAP, the neuroprotective action of VIP depends mainly on stimulation of astrocytes to produce and secrete factors of extremely high neuroprotective potential, including activity-dependent neurotrophic factor (ADNF) and activity-dependent neuroprotective protein (ADNP). It was shown that ADNF and ADNP, as well as their shortened derivatives ADNF-9 and NAP, prevent neurons from electrical blockade, excitotoxicity, apoE deficiency, glucose deficit, ischemia, toxic action of ethanol, beta-amyloid, and gp120. The neuroprotective potential of PHI has not been as thoroughly investigated yet, but recent data have confirmed that this peptide can also function as a neuroprotectant. It is thought that PACAP, VIP, and possibly PHI may serve as a goal of modern therapeutic strategies in various neurodegenerative disorders.

Disrupted circadian rhythms in VIP- and PHI-deficient mice

The related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) are expressed at high levels in the neurons of the suprachiasmatic nucleus (SCN), but their function in the regulation of circadian rhythms is unknown. To study the role of these peptides on the circadian system in vivo, a new mouse model was developed in which both VIP and PHI genes were disrupted by homologous recombination. In a light-dark cycle, these mice exhibited diurnal rhythms in activity which were largely indistinguishable from wild-type controls. In constant darkness, the VIP/PHI-deficient mice exhibited pronounced abnormalities in their circadian system. The activity patterns started approximately 8 h earlier than predicted by the previous light cycle. In addition, lack of VIP/PHI led to a shortened free-running period and a loss of the coherence and precision of the circadian locomotor activity rhythm. In about one-quarter of VIP/PHI mice examined, the wheel-running rhythm became arrhythmic after several weeks in constant darkness. Another striking example of these deficits is seen in the split-activity patterns expressed by the mutant mice when they were exposed to a skeleton photoperiod. In addition, the VIP/PHI-deficient mice exhibited deficits in the response of their circadian system to light. Electrophysiological analysis indicates that VIP enhances inhibitory synaptic transmission within the SCN of wild-type and VIP/PHI-deficient mice. Together, the observations suggest that VIP/PHI peptides are critically involved in both the generation of circadian oscillations as well as the normal synchronization of these rhythms to light.

Cyclic AMP formation in chicken brain: effect of vasoactive intestinal peptide, peptide histidine-isoleucine (PHI), and some PHI-related peptides

Vasoactive intestinal peptide (chicken form; chVIP), peptide histidine-isoleucine (porcine and rat forms; pPHI and rPHI), D-Phe(4) derivative of porcine PHI (D-Phe(4)-pPHI), peptide histidine-methionine (PHM; human PHI), and helodermin, were tested for their ability to stimulate cAMP production in [(3)H]adenine-prelabeled slices of chick cerebral cortex (CCx) and hypothalamus (HTh). The chVIP (0.1-3 microM) concentration-dependently and potently stimulated cAMP production in HTh and CCx; the responses observed after 3 microM of chVIP were comparable to those produced by 0.1 microM PACAP38. Helodermin (5 microM) moderately but significantly stimulated cAMP formation in both HTh and CCx, whereas pPHI, rPHI, PHM at 5 microM concentration only weakly affected cAMP production in CCx, and were inactive in HTh; D-Phe(4)-pPHI was inactive in both tissues. These data demonstrate that chVIP, PACAP, and to a lesser extent helodermin were capable of potently stimulating cAMP generation in the avian central nervous system. PHI-related peptides showed only weak or no activity, depending on the tissue.

A hVIPR transgene as a novel tool for the analysis of circadian function in the mouse suprachiasmatic nucleus

A mouse bearing a novel transgene encoding the human VPAC2 receptor (hVIPR; Shen et al. (2000) PNAS, 97, 11575-11580) was used to investigate circadian function in the hypothalamic suprachiasmatic nuclei (SCN). Neurons expressing hVPAC2R, detected by a beta-galactosidase (beta-GAL) tag, have a distinct distribution within the SCN, closely matching that of neurophysin (NP) neurons and extending into the region of peptide histidine isoleucine (PHI) cells. In common with NP and PHI cells, neurons expressing hVPAC2R are circadian in nature, as revealed by synchronous rhythmic expression of mPERIOD (mPER) proteins. A population of SCN cells not expressing PHI, NP or hVPAC2R exhibited circadian PER expression antiphasic with the rest of the SCN. Nocturnal light exposure induced mPER1 in the ventral SCN and mPER2 widely across the nucleus. Induction of nuclear mPER2 in hVPAC2R cells confirmed their photic responsiveness. Having established their circadian properties, we tested the utility of SCN neurons expressing the hVIPR transgene as functionally and anatomically explicit markers for SCN tissue grafts. Prenatal SCN tissue from hVIPR transgenic pups survived transplantation into adult CD1 mice, and expressed beta-GAL, PER and PHI. Over a series of studies, hVIPR transgenic SCN grafts restored circadian activity rhythms to 17 of 72 arrhythmic SCN lesioned recipients (23.6%). By using heterozygous hVIPR transgenic grafts on a heterozygous Clock mutant background we confirmed that restored activity rhythms were conferred by the donor tissue. We conclude that the hVIPR transgene is a powerful and flexible tool for examination of circadian function in the mouse SCN.

A hVIPR transgene as a novel tool for the analysis of circadian function in the mouse suprachiasmatic nucleus

A mouse bearing a novel transgene encoding the human VPAC2 receptor (hVIPR; Shen et al. (2000) PNAS, 97, 11575-11580) was used to investigate circadian function in the hypothalamic suprachiasmatic nuclei (SCN). Neurons expressing hVPAC2R, detected by a beta-galactosidase (beta-GAL) tag, have a distinct distribution within the SCN, closely matching that of neurophysin (NP) neurons and extending into the region of peptide histidine isoleucine (PHI) cells. In common with NP and PHI cells, neurons expressing hVPAC2R are circadian in nature, as revealed by synchronous rhythmic expression of mPERIOD (mPER) proteins. A population of SCN cells not expressing PHI, NP or hVPAC2R exhibited circadian PER expression antiphasic with the rest of the SCN. Nocturnal light exposure induced mPER1 in the ventral SCN and mPER2 widely across the nucleus. Induction of nuclear mPER2 in hVPAC2R cells confirmed their photic responsiveness. Having established their circadian properties, we tested the utility of SCN neurons expressing the hVIPR transgene as functionally and anatomically explicit markers for SCN tissue grafts. Prenatal SCN tissue from hVIPR transgenic pups survived transplantation into adult CD1 mice, and expressed beta-GAL, PER and PHI. Over a series of studies, hVIPR transgenic SCN grafts restored circadian activity rhythms to 17 of 72 arrhythmic SCN lesioned recipients (23.6%). By using heterozygous hVIPR transgenic grafts on a heterozygous Clock mutant background we confirmed that restored activity rhythms were conferred by the donor tissue. We conclude that the hVIPR transgene is a powerful and flexible tool for examination of circadian function in the mouse SCN.

Demonstration of nerve fibers immunoreactive to peptide N-terminal histidine C-terminal isoleucine (PHI) and vasoactive intestinal peptide (VIP) in the pig pineal gland

The pineal functions are modulated by some neuropeptides including PHI and VIP. The presence of PHI-immunoreactive and VIP-immunoreactive nerve fibers in the pineal gland has been shown in several mammalian species. Both peptides influence the pineal serotonin N-acetyltransferase activity and melatonin synthesis. The aim of the present study was to examine the localization of PHI- and VIP-immunoreactive nerve fibers in the pig pineal gland. Four three-month old female pigs housed in natural light conditions, with free access to food and water, were used in the study. The pineals were fixed by perfusion with 4% paraformaldehyde in 0.1 M phosphate buffer. An immunohistochemical ABC streptavidin-biotin-complex method was used for the demonstration of PHI and VIP. PHI- and VIP-immunopositive nerve fibers were found in the pineal gland as well as in the habenular and posterior commissural areas. In the pineal gland, the density of PHI-immunoreactive nerve fibers was considerably higher than that of the fibers containing VIP. PHI- and VIP-immunopositive nerve fibers were more abundant in the cortical than in the medullary part of the gland. The nerve fibers formed bundles in the pineal capsule, from where they penetrated to the connective tissue septa and formed a dense meshwork surrounding blood vessels. In the parenchyma, PHI- and VIP-immunoreactive nerve terminals created baskets around clusters of pinealocytes. No PHI- or VIP-immunopositive cells were found in the pig pineal gland.

Involvement of peptide histidine isoleucine in non-adrenergic non-cholinergic relaxation of the rat gastric fundus induced by high-frequency neuronal firing

The role of peptide histidine isoleucine (PHI) as a neurotransmitter of the inhibitory motor neurones, the physiological role of PHI and vasoactive intestinal polypeptide (VIP) in the non-adrenergic non-cholinergic (NANC) relaxation and the relative amounts of VIP- and PHI-like immunoreactivity (LI) co-released by neuronal activation were investigated in the rat gastric fundus. Longitudinal muscle strips from the rat gastric fundus precontracted by the thromboxane receptor agonist U46619 (0.1 micro M) were studied in organ baths under conditions of muscarinic receptor blockade by atropine (1 micro M) and adrenergic neurone blockade by guanethidine (5 micro M) ("NANC conditions"). Concentration-response curves were plotted for both amplitude and area under the curve (AUC) of the relaxant responses induced by VIP (0.3 nM-0.3 micro M), PHI (0.3 nM-1 micro M) and peptide histidine valine [PHV(1-42); 0.3 nM-1 micro M]. All three peptides were more potent in the curve based on amplitude than in that based on the AUC of relaxation. In addition, VIP was 5.3 and 7 times more potent than PHI and PHV(1-42), respectively, in producing relaxation expressed as amplitude, and 2.7 and 2.8 times, respectively, in producing relaxation expressed as AUC. PHI and PHV(1-42) behaved as partial agonists with respect to VIP in producing relaxation expressed as AUC. Electrical field stimulation (EFS; 120 mA, 1 ms, 4-32 Hz, pulse trains of 2 min) evoked frequency-dependent relaxant responses. Alpha-chymotrypsin (1 u/ml or 3 u/ml), an anti-VIP serum (1:100 or 1:50) and an anti-PHI serum (1:25), slightly reduced the amplitude, but greatly inhibited the AUC of the NANC relaxation induced by EFS (13 Hz) [approximately 72%, 47% and 28% less than that seen in time controls or with normal rabbit serum (1:100 or 1:25), respectively]. EFS (8-32 Hz) caused significant, frequency-dependent increases in the outflow of VIP- and PHI-LI from the strips. The EFS-induced release of VIP-LI was approximately 20% of the PHI-LI release. These findings indicate that PHI is involved in EFS-induced NANC relaxation of the rat gastric fundus, the major physiological role of VIP and PHI is the maintenance of smooth muscle relaxation and VIP is co-released in equimolar amounts mainly with PHI.

The VPAC(2) receptor is essential for circadian function in the mouse suprachiasmatic nuclei

The neuropeptides pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are implicated in the photic entrainment of circadian rhythms in the suprachiasmatic nuclei (SCN). We now report that mice carrying a null mutation of the VPAC(2) receptor for VIP and PACAP (Vipr2(-/-)) are incapable of sustaining normal circadian rhythms of rest/activity behavior. These mice also fail to exhibit circadian expression of the core clock genes mPer1, mPer2, and mCry1 and the clock-controlled gene arginine vasopressin (AVP) in the SCN. Moreover, the mutants fail to show acute induction of mPer1 and mPer2 by nocturnal illumination. This study highlights the role of intercellular neuropeptidergic signaling in maintenance of circadian function within the SCN.

Identification of a potential receptor for both peptide histidine isoleucine and peptide histidine valine

Peptide histidine isoleucine (PHI), peptide histidine valine (PHV), and vasoactive intestinal polypeptide (VIP) are cosynthesized from the same precursor and share high levels of structural similarities with overlapping biological functions. In this study, the first PHI/PHV receptor was isolated and characterized in goldfish. To study this receptor using homologous peptides, we have also characterized the goldfish prepro-PHI/VIP, and, surprisingly, a shorter transcript lacking the VIP coding region was isolated. A PHI/VIP precursor without the VIP coding sequence has never before been reported. Initial functional expression of the PHI/PHV receptor in Chinese hamster ovary cells revealed that it could be activated by human PHV [50% effective concentration (EC(50)): 43 nM] and to a lesser extent human PHI (EC(50): 133 nM) and helodermin (EC(50): 166 nM) but not fish and mammalian pituitary adenylate cyclase-activating polypeptides and VIPs. Subsequent studies indicated that, similar to the pituitary adenylate cyclase-activating polypeptide receptors (PAC1-R, VPAC1-R, and VPAC2-R), the receptor isolated in this study is able to interact with goldfish PHI and its C-terminally extended form, PHV with EC(50) values 93 and 43 nM, respectively. Northern blot and RT-PCR/Southern blot analyses revealed that the PHI/VIP gene is expressed in the intestine, brain, and gall bladder and the PHI/PHV receptor gene is primarily expressed in the pituitary and to a lesser extend in the intestine and gall bladder, suggesting that PHI/PHV may play a role, notably in the regulation of pituitary function. In conclusion, our results demonstrate for the first time the existence of a PHI/PHV receptor, indicating that the functions of PHI and PHV could be mediated by their own receptor in addition to VIP receptors.

The polypeptide PHI discriminates a GTP-insensitive form of VIP receptor in liver membranes

In early reports on 125I-VIP binding experiments in liver membranes, it has been proposed that, the VIP binding sites were partially sensitive to GTP. Here we confirm that the VIP binding sites of chicken liver membranes consisted mainly in bivalent VIP/PACAP receptors and that about 50% of the 125I-VIP binding capacity was not affected by the GTP analogue GppNHp. Part of these bivalent receptors also appeared to represent PHI binding sites. In GppNHp-treated membranes, the GTP-insensitive VIP binding sites displayed a 17-fold higher relative affinity than in control membranes for the VIP analogue PHI. Such data suggested that GTP-insensitive VIP receptors may correspond to a subclass of high-affinity PHI receptors. Cross-linking of 125 I-VIP or 125 I-PHI to their receptors, revealed 2 components of 48 and 60 kDa. The radiolabelling of the 60 kDa component was strongly affected by increasing concentrations of the GTP analogue but was modestly abolished by an excess of PHI. Conversely, the radiolabelling of the 48 kDa molecular form was not affected by the GTP analogue but was efficiently abolished by increasing concentrations of PHI. Taken together, the data suggest that the 48 kDa component expressed in chicken liver membranes display the properties of a GTP-insensitive VIP/PHI receptor that can be pharmacologically discriminated from the GTP-sensitive 60 kDa form, through its much higher affinity for PHI.

A C-terminally elongated form of PHI from porcine intestine

A C-terminally elongated form of peptide histidine isoleucine amide (PHI) was isolated from porcine intestine based on its effect on cAMP production in IMR-32 cells. The structure was determined by amino acid sequence analysis of tryptic fragments and by mass spectrometry. The peptide has 42 amino acid residues like those described from human, rat and mouse, but the amino acid sequence of the C-terminal extension of pig PHI is unique. Unlike the other peptides, it has a C-terminal Ala and it differs at five positions from the human form and at six positions from the rat form, while the human and the rat forms differ by only two substitutions. To avoid confusion arising from different C-terminal residues, a unifying nomenclature is proposed: PHI-27 for the hormone and PHI-42 for the elongated product.

Innervation of the sheep pineal gland by nonsympathetic nerve fibers containing NADPH-diaphorase activity

We used the NADPH-diaphorase histochemical method as a potential marker for nitric oxide synthase (NOS)-containing nerve fibers innervating the pineal gland of the sheep. Nerve fibers containing NADPH-diaphorase activity provide dense innervation of the sheep pineal gland. The nerve fibers were located in the pineal capsule, in the connective tissue septae separating the lobull of the gland, and penetrating between the pinealocytes. The nerve fibers were either smooth or endowed with boutons en passant. After bilateral removal of the superior cervical ganglion, the dense network of NADPH-diaphorase-positive fibers was still present in the gland. Ganglionectomy affected neither the distribution nor the appearance of the NADPH-diaphorase-positive fibers. Most of the NADPH-diaphorase-positive fibers also contained peptide histidine isoleucine and vasoactive intestinal polypeptide, and a comparatively smaller fraction contained neuropeptide Y. Pinealocytes never exhibited NADPH-diaphorase activity. These results demonstrate a major neural input to the sheep pineal gland with NADPH-diaphorase-positive nerve fibers of nonsympathetic origin.

Vasoactive intestinal polypeptide-like and peptide histidine isoleucine-like proteins excreted/secreted by Nippostrongylus brasiliensis, Nematodirus battus and Ascaridia galli

Vasoactive intestinal polypeptide (VIP)-like protein was detected by dot blot analysis in the excretions/secretions (E/S) of Nematodirus battus and Ascaridia galli and was confirmed in the E/S of Nippostrongylus brasiliensis. ELISA analysis showed that N. brasiliensis E/S contained the highest proportion of VIP-like protein (28.04 pmoles/mg of total E/S protein) and A. galli E/S contained the lowest (10.89 pmoles/mg of total E/S protein). Peptide histidine isoleucine (PHI)-like protein was detected by dot blot analysis in the E/S products of N. brasiliensis, N. battus and A. galli. ELISA analysis suggested that A. galli E/S contained the highest proportion of PHI (20.77 nmoles/mg of total E/S protein) and N. battus E/S contained the lowest (0.67 nmoles/mg of total E/S protein). The possible significance of VIP-like and PHI-like substances in the E/S of gastrointestinal nematodes is discussed.

Vasoactive intestinal peptide (VIP)1 receptor. Three nonadjacent amino acids are responsible for species selectivity with respect to recognition of peptide histidine isoleucineamide

Vasoactive intestinal peptide (VIP)1 receptors in rats and humans recognize peptide histidine isoleucineamide (PHI) with high and low affinity, respectively. We took advantage of this phenotypic difference to identify the domain responsible for the selective recognition of PHI by rat and human receptors which display >80% sequence identity. After transfection of human and rat receptors in COS cells, the ratio of IC50 for PHI/IC50 for VIP (referred to as P/V) in inhibiting 125I-VIP binding was shown to be >1,000 and <40, respectively. Construction of eight rat/human receptor chimerae by overlap polymerase chain reaction and determination of their P/V ratios demonstrated that the critical domain for PHI recognition is present within a sequence comprising part of the first extracellular loop and third transmembrane domain. This domain contains three different amino acids numbered according to human and rat sequences, respectively, e.g. Gln207 (human) versus His208 (rat), Gly211 versus Ala212 and Met219 versus Val220. Site-directed mutagenesis introducing individual, double, or triple mutations in a chimeric construct revealed that all three amino acids were involved in the recognition of PHI. Triple mutations were then introduced in the wild-type receptors i.e. Q207H, G211A, M219V human VIP1 receptor and H208Q, A212G, V220M rat VIP1 receptor, resulting in a complete change in their phenotype from human to rat and from rat to human, respectively. The results demonstrate that three nonadjacent amino acids are responsible for the selective recognition of PHI by human and rat VIP1 receptors.

Presence of nitric oxide synthase in the sheep pineal gland: an experimental immunohistochemical study

By use of immunohistochemistry, a dense network of nerve fibres immunoreactive to the neuronal form of nitric oxide synthase (NOS, subtype I) was demonstrated in the pineal gland of sheep. The NOS-immunoreactive fibres were located in the pineal capsule and the connective tissue septae of the gland, but fibres were also present intraparenchymally between the pinealocytes. NOS-immunoreactive nerve fibres were still present in the gland 1 month after bilateral removal of the superior cervical ganglia. By use of an antibody directed against endothelial NOS (subtype III), only pineal blood vessels were stained. This staining was still present in the ganglionectomized animals. No difference was found in the staining between the control animals and the ganglionectomized ones. The pinealocytes were not stained, neither by the antibody against neuronal NOS nor by the antibody against endothelial NOS. By use of double immunohistochemical stainings, NOS was in many nerve fibres colocalized with vasoactive intestinal peptide. Western blot analysis of supernatant fractions of sheep pineal homogenates showed the presence of a band corresponding to the neuronal NOS. Thus, the present data show a prominent innervation of the sheep pineal gland with NOS-immunoreactive nerve fibres with their origin outside the sympathetic nervous system, indicating an influence of NO on the pinealocyte metabolism from non-sympathetic nerve fibres in this species. The presence of NOS in both perivascular nerve fibres and the endothelium of the blood vessels of the gland suggests a role of NO in the regulation of the circulation of the sheep pineal gland.

In situ hybridization histochemistry of vgf mRNA in the rat suprachiasmatic nucleus: co-localization with vasopressin/neurophysin and VIP/PHI

The expression of vgf gene, first isolated as a gene induced by nerve growth factor in PC12 cells, was investigated in neurons of the suprachiasmatic nucleus (SCN) by in situ hybridization. In the rat forebrain, the vgf mRNA was found most densely in the SCN. Neurons which express vgf mRNA were found both in the dorsomedial and ventrolateral subdivisions. Soluble-labeling of vgf in situ hybridization and peptide immunocytochemistry demonstrated that vgf mRNA was expressed in most vasopressin- and neurophysin-immunoreactive neurons in the dorsomedial part and in vasoactive intestinal peptide (VIP)- and peptide histidine isoleucine amide (PHI)-immunoreactive neurons in the ventrolateral part. These findings suggest that vgf is a highly expressed gene in both vasopressin/neurophysin neurons and VIP/PHI neurons which were speculated to be involved in the generation and entrainment of circadian rhythm.

Sequence of a cDNA encoding chicken vasoactive intestinal peptide (VIP)

Mammalian pre-pro-vasoactive intestinal peptide (pre-proVIP) gives rise to the neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine amide (PHI). The cDNA encoding chicken VIP was cloned and sequenced. The region of chicken pre-proVIP homologous to the mammalian PHI region is not followed by an amidation signal. This unusual feature suggests that processing of the precursor may be different in the chicken.

Peptidergic innervation of the human testis and epididymis

Neuropeptidergic innervation of the human testis and epididymis was investigated by immunohistochemical methods. The innervation of the epididymis was more dense than that of testis. In the testis only tyrosine hydroxylase- and neuropeptide Y-positive nerves could be found between seminiferous tubules and around blood vessels. In the connective tissue capsule of the testis also small calcitonin gene-related peptide- and metenkephalin-containing nerve fibres were seen. The epididymis was densely innervated by nerve fibres immunoreactive to tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, calcitonin gene-related peptide, galanin, peptide histidine isoleusine and substance P.

Vagal-induced tachycardia: release of vasoactive intestinal peptide and peptide HI

The relationship between vagal-induced tachycardia (VT) and release of vasoactive intestinal peptide (VIP) and peptide HI (PHI) into cardiac lymph and coronary sinus blood was studied in 23 alpha-chloralose-anesthetized open-chest dogs that were autonomically decentralized and pretreated with atropine and propranolol. After simultaneous right and left cervical vagal stimulation at 5 V, 20 Hz for 3 min mean +/- SE, increase in heart rate was 38 +/- 6 beats/min, and increase in lymph VIP output from control was 0.308 +/- 0.093 pg/min (P = 0.004). The decrease in VIP arterial minus coronary sinus concentration was not significant. The increase in heart rate did not significantly correlate with increase in lymph VIP output (R2 = 0.141) or decrease in VIP arterial minus coronary sinus concentration (R2 = 0.059). The increases in heart rate and lymph VIP output were blocked by hexamethonium. Increase in lymph PHI output from control during VT (5 dogs) was 0.797 +/- 0.658 pg/min. Arterial-coronary sinus PHI concentration difference did not change in these dogs. These data indicate that VT is associated but not significantly correlated with VIP and PHI release into cardiac lymph. Cholinoceptive nicotinic receptors may mediate VIP release and VT in anesthetized dogs.

Peptide histidine isoleucine-like immunoreactivity release from the rat gastric fundus

1. Longitudinal muscle strips from the rat gastric fundus were subjected to in vitro electrical field stimulation (EFS) under non-adrenergic non-cholinergic (NANC) conditions to study the release of peptide histidine isoleucine-like immunoreactivity (PHI-LI) and the correlation between PHI-LI release and NANC relaxation. 2. Different radioimmunoassay (RIA) systems employing C-terminal- and N-terminal-specific anti-PHI sera were used to determine the relative contributions of PHI and its C-terminally extended forms, peptide histidine glycine (PHI-Gly) and peptide histidine valine [PHV(1-42)], to the PHI-LI released by the rat gastric fundus. 3. In the presence of atropine (1 microM) and guanethidine (5 microM), EFS (120 mA, 1 ms, 0.25-32.0 Hz, trains of 2 min) induced frequency-dependent relaxations of 5-hydroxytryptamine (3 microM) pre-contracted strips. 4. EFS at frequencies of 8-32 Hz evoked significant increases in PHI-LI outflow. The increases in PHI-LI outflow evoked by 16-Hz EFS were abolished by tetrodotoxin (3 microM) and by a calcium-free medium, indicating an active release process from intramural nerves. 5. The EFS-induced release of PHI-LI measured with the N-terminal-specific antiserum was significantly greater than that detected with the C-terminal-specific antisera. 6. Sephadex G-25 gel permeation chromatographic analysis was performed on the PHI-LI release in response to 32-Hz EFS. A C-terminal-specific antiserum revealed one peak co-eluting with the rat PHI standard. When PHI-LI was measured with the N-terminal-specific antiserum, two peaks were found that co-eluted with the rat PHV(1-42) and rat PHI-Gly/PHI standards, respectively. 7. The present data suggest that the extended forms of PHI are the primary components of the PHI-LI released by NANC inhibitory neurones in the rat gastric fundus and support a NANC inhibitory neurotransmitter role for PHI and its extended forms in this tissue.

Concentrations and distribution of vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI) and peptide histidine valine (PHV) in the cerebral cortex and the suprachiasmatic nucleus of the mouse

Prepro-vasoactive intestinal peptide (prepro-VIP) is processed to at least three biologically active peptides: VIP, peptide histidine isoleucine (PHI) and an extended PHI, peptide histidine valine (PHV). The aim of the present investigation was by chromatography combined with RIA and immunocytochemistry to determine which of these peptides were present in the cerebral cortex and the hypothalamic suprachiasmatic nucleus (SCN) of the mouse. These regions were chosen since they are known to contain a high concentration of VIP but the relative concentration of PHI and PHV is not known. Tissue was extracted and subjected to gel chromatography and high-pressure liquid chromatography (HPLC). VIP and PHI immunoreactivities co-eluted with synthetic rat VIP and PHI. A minor peak of PHI and prepro-VIP(111-122) immunoreactivities eluted at the position of synthetic PHV. Surprisingly, a major peak of prepro-VIP(111-122) immunoreactivity eluted in a position not related to any other immunoreactivity indicating the presence of prepro-VIP(111-122). Measurements of these immunoreactivities in cortical and suprachiasmatic extracts revealed that VIP was found in the highest concentration whereas PHV was found in the lowest. Immunoreactivity for PHI and prepro-VIP(111-122) was found in moderate concentrations. Except for prepro-VIP(111-122) which was found to be approximately 3 x higher concentrated in the SCN than in the cerebral cortex, the other immunoreactivities were found in almost similar relative concentrations in the two tissues. Using immunocytochemistry, elongated neurons mostly of the bipolar type with prominent processes observed in the cerebral cortex reacted with all antisera tested. More PHI/PHV/prepro-VIP(111-122)- than VIP-immunoreactive (ir) nerve fibers were found in the cerebral cortex. In the SCN, the density of immunoreactivity was the same whatever antiserum used. VIP-, PHI- and prepro-VIP(111-122)/PHV-ir neurons were observed in the ventral part of the nucleus with numerous axons coursing caudodorsally into the subparaventricular area. A substantial number of terminals was detected caudal to the paraventricular nucleus. Minor projections spread to the medial part of the anterior nucleus and to the medial preoptic area hypothalamic. These data show that VIP and PHI are the major active peptides derived from prepro-VIP in the mouse cerebral cortex and SCN whereas PHV was found in minor concentrations. Prepro-VIP(111-122), which so far has been found to have no functional significance, is, therefore, most likely a vaste fragment of processing of PHI in central neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Density of peptide histidine-isoleucine- and vasoactive intestinal peptide-immunoreactive nerve fibers in the sheep pineal gland is not affected by superior cervical ganglionectomy

Peptide histidine-isoleucine (PHI) is a regulatory peptide, synthesized as part of the same propeptide that includes also vasoactive intestinal peptide (VIP). The present study describes the distribution of PHI-immunoreactive nerve fibers in the sheep pineal organ and compares their location with the distribution of VIP-immunoreactive fibers in both normal and superior cervical ganglionectomized sheep in order to elucidate the origin of the PHI/VIP immunoreactive nerve fibers. Several PHI-immunoreactive nerve fibers were present in the meninges and in the pineal capsule. Numerous positive nerve fibers entered the pineal gland and travelled within connective tissue spaces. Individual PHI-positive nerve fibers were either smooth, without specialization, or varicose. Generally VIP- and PHI-immunoreactive fibers were located close to connective septa and blood vessels. However, many PHIergic and VIPergic fibers possessing varicosities of variable sizes were also dispersed between pinealocytes. The distribution, density, and morphology of PHI- and VIP-immunoreactive fibers in the sheep pineal gland were similar. In superior cervical ganglionectomized animals, intrapineal VIP- and PHI-immunoreactive nerve fibers were present with the same density as in control animals. In agreement, the concentration of immunoreactive VIP and PHI did not change after ganglionectomy. No VIP- and PHI-immunoreactive cell bodies were observed in the superior cervical ganglia. Thus this study shows that the intrapineal VIP- and PHI-immunoreactive nerve fibers do not originate from the sympathetic superior cervical ganglion.

Location of PHM/VIP mRNA in human gastrointestinal tract detected by in situ hybridization

The expression of the gene for vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM) in the human gastrointestinal tract was studied by in situ hybridization and Northern blotting for PHM/VIP mRNA and immunocytochemistry using specific antisera against the bioactive peptides PHM and VIP. In the colon sigmoideum, antisera against all five putative processing products of the VIP precursor (prepro-VIP) were used, namely prepro-VIP 22-79, PHM, prepro-VIP 111-122, VIP and prepro-VIP 156-170. Furthermore, RNA extracted from various regions of the gastrointestinal tract was examined by Northern blots and hybridization to a VIP-cDNA probe. Throughout the gastrointestinal tract, PHM/VIP mRNA was found in neurons only. Using single- or double-staining methods, we demonstrated both PHM/VIP mRNA and the corresponding peptides PHM and VIP in the neurons. In the sigmoideum, the single-staining methods were extended to investigate whether the neurons simultaneously contained PHM/VIP mRNA and each of the five prepro-VIP-derived peptides. Only one major band of PHM/VIP mRNA (1.9 kb) was found by Northern blotting in the tissue of the gastrointestinal tract.

Serotoninergic and peptidergic nerve elements in the protoscolex of Echinococcus granulosus (Cestoda, Cyclophyllidea)

The localisation and distribution of 5-hydroxytryptamine (5-HT, or serotonin) and neuropeptides in the nervous system of the protoscolex of the hydatid organism Echinococcus granulosus were determined by an indirect immunofluorescence technique. Nerve-cell bodies immunoreactive for 5-HT occurred in the lateral ganglia and in association with the lateral longitudinal nerve cords. 5-HT immunostaining was also evident in the central nerve ring, in the rostellar nerves and in the nerve plexus innervating the suckers. Of the antisera used to screen the protoscolex for neuropeptide immunoreactivity (IR), immunostaining was obtained with those raised against pancreatic polypeptide (PP), peptide YY (PYY), substance P (SP), peptide histidine isoleucine (PHI) and vasoactive intestinal peptide (VIP). The most extensive pattern of IR occurred with antisera to PP and PYY. Immunoreactive nerve elements were evident in the lateral ganglia, central nerve ring, rostellar nerves, rostellar ganglia, sucker plexus and longitudinal nerve cords. The distribution of SP-, PHI- and VIP-IRs was more restricted: SP-IR occurred in the lateral ganglia and sucker nerves, whilst PHI- and VIP-immunoreactive nerve elements were associated with the lateral longitudinal nerve cords. Protoscoleces cultured in vitro for 29 days were also examined and neuroanatomical changes noted. A greater development of the longitudinal nerve cords and their cross-connectives in the body of the worm was evident, and a group of nerve cells were seen to develop at the posterior end of the main lateral nerve cords.

The presence of nerve fibers immunoreactive for vasoactive intestinal peptide (VIP), peptide histidine isoleucine (PHI), and preproVIP(111-122) in the mouse pineal gland

A low to moderate number of vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI)-immunoreactive nerve fibers with prominent boutons-en-passage were demonstrated in the pineal gland of the mouse. The two peptides, which are parts of the same precursor molecule, were distributed identically in the gland. Positive fibers were present in the connective tissue septae in the gland, in the pineal capsule, and in the pineal parenchyma. No VIP-PHI-immunoreactive elements were found in the deep pineal gland, in the pineal stalk, or in habenular and posterior commissures. This morphological distribution of immunoreactive nerve fibers, which is similar to the distribution in other mammals, indicates that the VIP/PHI fibers of the mouse pineal gland originate exclusively from perikarya in a peripheral ganglion, presumably one of the cholinergic ganglia of the head. No evidence for a VIPergic central innervation was found. VIP and PHI are connected via a bridging peptide equivalent to amino acids 111-122 of the precursor (preproVIP(111-122)). In order to demonstrate the possible existence of this peptide in intra-pineal nerve fibers, antisera directed against a synthetic sequence identical to preproVIP(111-122) and immunohistochemistry were applied. PreproVIP(111-122)-immunoreactive nerve fibers were observed in the mouse pineal gland, with the same distribution pattern and morphology as those immunoreactive for VIP and PHI. To quantify the peptide-immunoreactivities, 50 mice pineals were pooled, extracted, and the concentrations were measured radioimmunologically. The concentrations of the VIP and preproVIP(111-122) immunoreactivities were 1.7 and 2.0 pmol/g, respectively, whereas the concentration of PHI was 0.9 pmol/g.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural studies on peptides in the dorsal horn of the spinal cord--I. Co-existence of galanin with other peptides in primary afferents in normal rats

The aim of the present study was to investigate galanin-like immunoreactivity in primary afferent terminals and its relationship to other neuropeptides in laminae I and II of the fourth and fifth lumbar segments of normal rat spinal cord using immunofluorescence and pre- and post-embedding electron-microscopic immunocytochemistry. Triple-immunofluorescence staining showed that galanin-like immunoreactivity co-localized with substance P- and calcitonin gene-related peptide-like immunoreactivities in many nerve fibres and terminals in laminae I and II of the dorsal horn. At the ultrastructural level, using pre-embedding immunocytochemistry, galanin-like immunoreactivity was found in type I glomeruli with an electron-dense central terminal containing many densely packed synaptic vesicles and several large dense-core vesicles. Both the cytoplasm and the core of the large vesicles were immunoreactive. In type II glomeruli with an electron-lucent central terminal and loosely packed synaptic vesicles the large dense-core vesicles and the cytoplasm were only weakly galanin-positive. Post-embedding immunocytochemistry revealed that galanin-like immunoreactivity co-existed with substance P- and calcitonin gene-related peptide-like immunoreactivities in many terminals and in individual large dense-core vesicles in lamina II. These terminals were considered to represent primary afferents, since there is evidence that calcitonin gene-related peptide in the dorsal horn only occurs in nerve endings originating in dorsal root ganglia. Evidence was also unexpectedly obtained for the occurrence of several other peptides in calcitonin gene-related peptide-positive terminals, i.e. in presumably primary afferents. Thus galanin-like immunoreactivity sometimes also co-localized with cholecystokinin- and neuropeptide tyrosine-like immunoreactivities in calcitonin gene-related peptide-immunoreactive terminals and in some large dense-core vesicles in such terminals. A small number of calcitonin gene-related peptide immunoreactive, presumably primary afferent terminals contained enkephalin-, neurotensin- (and galanin-)like immunoreactivities. These results indicated that galanin can be co-stored with several other neuropeptides in large dense-core vesicles in primary afferent terminals and may presumably be released together with them in the superficial layer of the dorsal horn. Since various combinations of peptides, presumably at varying concentrations, occur in the large dense-core vesicles in a given nerve ending, it is likely that the individual large dense-core vesicles produced in a neuron are heterogenous with regard to peptide content and thus to the message that they transmit upon release.

Large calibre primary afferent neurons projecting to the gracile nucleus express neuropeptide Y after sciatic nerve lesions: an immunohistochemical and in situ hybridization study in rats

Using immunohistochemistry and in situ hybridization, we studied changes in expression of some neuropeptides in large and medium-sized neurons in lumbar 4 and 5 rat dorsal root ganglia projecting to the gracile nucleus, in response to peripheral axotomy. Fourteen days after unilateral sciatic nerve transection, many large neurons and some medium-sized neurons in ipsilateral dorsal root ganglia were strongly neuropeptide Y-positive. Galanin-, vasoactive intestinal polypeptide (VIP)- and peptide histidine-isoleucine (PHI)-like immunoreactivities coexisted with neuropeptide Y-like immunoreactivity in some of these neurons. After axotomy numerous large and medium-sized cells contained neuropeptide Y mRNA in the ipsilateral ganglia, whereas no hybridization was seen in the contralateral or control ganglia. Cross-sectioned, large neuropeptide Y-positive fibres were observed in a somatotopically appropriate zone within the ipsilateral gracile fasciculus. A dense network of neuropeptide Y-immunoreactive, large nerve fibres and terminals was seen in the ipsilateral gracile nucleus. A small number of galanin- and VIP/PHI-like immunoreactive nerve fibres and terminals were also observed in adjacent sections. Neuropeptide Y-like immunoreactivity colocalized with galanin- or VIP/PHI-like immunoreactivity in some nerve fibres. None of these neuropeptide immunoreactivities could be detected in nerve fibres and terminals in the control or contralateral gracile nucleus. These findings suggest that neuropeptides, in addition to their role in small dorsal root ganglion neurons, may have a function in large and medium-sized dorsal root ganglion neurons projecting to laminae III and IV in the dorsal horn as well as to the gracile nuclei, as a part of their response to peripheral axotomy.

VIP-mediated G protein-coupled Ca2+ influx activates a constitutive NOS in dispersed gastric muscle cells

Vasoactive intestinal peptide (VIP) and peptide histidine-isoleucine (PHI) receptors and the signaling pathways to which they are coupled were characterized in dispersed gastric smooth muscle cells. Radioligand binding using 125I-labeled VIP and PHI identified 4 classes of receptors: VIP-preferring and PHI-preferring receptors recognized by both ligands and readily desensitized by the preferred ligand, and VIP-specific and PHI-specific receptors recognized by only 1 ligand and resistant to desensitization. All except VIP-specific receptors were coupled to adenylate cyclase. VIP-specific receptors mediated a G protein-coupled Ca2+ influx that led to activation of NO synthase (NOS), NO-dependent activation of soluble guanylate cyclase, and activation of guanosine 3',5'-cyclic monophosphate (cGMP) kinase resulting in muscle relaxation. The entire cascade was blocked by Ca2+ channel and/or calmodulin antagonists. The NOS inhibitor NG-nitro-L-arginine abolished L-[3H]citrulline (coproduct of NO synthesis) and cGMP generation and partly inhibited (52 +/- 4%) relaxation. The components of response mediated by VIP-specific receptors (increase in [Ca2+]i, L-[3H]citrulline, and cGMP) were preserved after desensitization. Insertion of guanosine 5'-O-(beta-thio)diphosphate into reversibly permeabilized muscle cells abolished responses mediated by VIP-preferring and VIP-specific receptors. VIP stimulated both adenosine 3',5'-cyclic monophosphate (cAMP)-kinase and cGMP-kinase activities consistent with stimulation of cAMP and cGMP. Both kinases contributed to relaxation that was partly inhibited by cAMP-kinase [H-89 and (R)-p-adenosine 3',5'-cyclic monophosphorothioate] and cGMP-kinase (KT-5823) inhibitors and abolished by a combination of the 2 types of inhibitors. We conclude that VIP-specific receptors mediate a G protein-coupled Ca2+ influx leading to activation of a constitutive Ca2+/calmodulin-dependent NOS and generation of NO, which is partly responsible for relaxation in smooth muscle.

Expression of functional receptors for vasoactive intestinal peptide in freshly isolated and cultured gastric muscle cells

Vasoactive intestinal peptide (VIP) receptors were characterized in freshly isolated and cultured smooth muscle cells from guinea pig stomach by radioligand binding and by measurement of relaxation in single isolated and cultured cells. 125I-VIP bound to both freshly isolated and cultured muscle cells: binding was rapid, specific, saturable and temperature-dependent, and was inhibited in a concentration-dependent fashion by VIP, VIP10-28, PHI and secretin, in this order. Competition curves for VIP could be resolved into high- and low-affinity components, yielding similar binding constants in freshly isolated and cultured cells (high-affinity Kd 0.11 and 0.22 nM; low-affinity Kd 59 and 37 nM; high-affinity binding sites: 1183 and 1021 per cell, representing about 1% of total binding sites). VIP10-28 inhibited 125I-VIP binding completely and acted as potent competitive antagonist of VIP-induced relaxation (Ki 0.5 nM). PHI and secretin, however, inhibited partly 125I-VIP binding: the pattern of inhibition implied that VIP interacts with VIP-preferring receptors that are recognized by PHI and secretin as well as with VIP-specific receptors. The pattern of binding is consistent with recent evidence indicating that VIP activates two signalling pathways, a VIP-specific, nitric oxide/cGMP-dependent pathway and a common cAMP-dependent pathway shared by all three peptides. PHI and secretin were relatively more potent as relaxant agents than as inhibitors of 125I-VIP binding raising the possibility that PHI and secretin could interact additionally with PHI- and secretin-preferring receptors in mediating relaxation.

Vasoactive intestinal peptide/peptide histidine isoleucine mRNA in the eye and suprachiasmatic nucleus of normal and monocularly enucleated rats

The localization of the messenger RNA (mRNA) encoding vasoactive intestinal peptide/peptide histidine isoleucine (VIP/PHI) in the rat eye was studied by in situ hybridization histochemistry using a synthetic 35S-labeled oligodeoxyribonucleotide. Among the layers of the retina, specific labeling was found in the soma of some cells in the innermost lamina of the inner nuclear layer. Occasionally, labeled cells were also present in the ganglion cell layer. No specific labeling was detected in any ocular structures other than the retina, including the cornea, iris, ciliary body, choroid, choriocapillaris, optic nerve and sclera. We also examined VIP/PHI mRNA expression in the suprachiasmatic nucleus (SCN) of the hypothalamus, which is the pacemaker of circadian rhythms and synchronizes them with the environmental light-dark cycle. High labeling was found in the ventrolateral part of the nucleus, which is the site of most projections from the retina. Monocular enucleation of rats at birth resulted in an increase of VIP/PHI mRNA expression in SCN ipsilateral to the removed eye after postnatal day 60. The discrete pattern of hybridization for VIP/PHI mRNA indicates that these two peptides are synthetized in rat retina and SCN and suggests that they may play a key role in the photic entrainment to the SCN regulating various circadian rhythms.

Dipeptidyl-peptidase IV hydrolyses gastric inhibitory polypeptide, glucagon-like peptide-1(7-36)amide, peptide histidine methionine and is responsible for their degradation in human serum

Peptides of the glucagon/vasoactive-intestinal-peptide (VIP) peptide family share a considerable sequence similarity at their N-terminus. They either start with Tyr-Ala, His-Ala or His-Ser which might be in part potential targets for dipeptidyl-peptidase IV, a highly specialized aminopeptidase removing dipeptides only from peptides with N-terminal penultimate proline or alanine. Growth-hormone-releasing factor (1-29)amide and gastric inhibitory peptide/glucose-dependent insulinotropic peptide (GIP) with terminal Tyr-Ala as well as glucagon-like peptide-1(7-36)amide/insulinotropin [GLP-1(7-36)amide] and peptide histidine methionine (PHM) with terminal His-Ala were hydrolysed to their des-Xaa-Ala derivatives by dipeptidyl-peptidase IV purified from human placenta. VIP with terminal His-Ser was not significantly degraded by the peptidase. The kinetics of the hydrolysis of GIP, GLP-1(7-36)amide and PHM were analyzed in detail. For these peptides Km values of 4-34 microM and Vmax values of 0.6-3.8 mumol.min-1.mg protein-1 were determined for the purified peptidase which should allow their enzymic degradation also at physiological, nanomolar concentrations. When human serum was incubated with GIP or GLP-1(7-36)amide the same fragments as with the purified dipeptidyl-peptidase IV, namely the des-Xaa-Ala peptides and Tyr-Ala in the case of GIP or His-Ala in the case of GLP-1(7-36)amide, were identified as the main degradation products of these peptide hormones. Incorporation of inhibitors specific for dipeptidyl-peptidase IV, 1 mM Lys-pyrrolidide or 0.1 mM diprotin A (Ile-Pro-Ile), completely abolished the production of these fragments by serum. It is concluded that dipeptidyl-peptidase IV initiates the metabolism of GIP and GLP-1(7-36)amide in human serum. Since an intact N-terminus is obligate for the biological activity of the members of the glucagon/VIP peptide family [e. g. GIP(3-42) is known to be inactive to release insulin in the presence of glucose as does intact GIP], dipeptidyl-peptidase-IV action inactivates these peptide hormones. The relevance of this finding for their inactivation and their determination by immunoassays is discussed.

Effects of damage to SCN neurons and efferent pathways on circadian activity rhythms of hamsters

This experiment was designed to determine if entrainment to a light:dark (LD) schedule and the free-running rhythm in constant light are altered by partial lesions of suprachiasmatic nuclei (SCN) cells or SCN output pathways. Twenty-four male golden hamsters were housed under 12L:12D. Hamsters received either lesions (n = 16), sham surgery (n = 4), or no surgery (n = 4), and were placed into individual cages with running wheels under 14L:10D. Each time after 4 weeks, the LD schedule was phase advanced by 6 h, phase delayed by 6 h, and then the animals were exposed to constant dim light. At the end of the experiment, brain sections were processed for peptide histidine isoleucine (PHI) and gastrin releasing peptide (GRP) immunohistochemistry. Alternate sections were stained for cells and fibers. Behavioral results indicate that (a) very few SCN cells and SCN efferent fibers, as labeled by PHI and GRP immunohistochemistry, are necessary for the expression of circadian rhythmicity in wheel running, and (b) damage to pathways rostral to the SCN may be more critical for entrainment and rhythmicity than damage to caudal pathways. Targets of PHI- and GRP-immunoreactive SCN efferent fibers were also identified.

Evidence for involvement of nitric oxide in the regulation of hypothalamic portal blood flow

Vasoactive intestinal polypeptide and peptide histidine isoleucine, two peptides with a common precursor and with strong vasodilatory actions, have been suggested to be involved in control of blood flow through the hypothalamic portal blood vessels, in this way regulating the amounts of releasing and inhibitory factors reaching the anterior pituitary. Using the indirect immunofluorescence technique, we now show that this system also contains the enzyme nitric oxide synthase, as well as acetylcholinesterase. It is therefore likely that the control of blood flow through the portal vessels is mediated via relaxation of smooth muscle cells with a high myogenic tone by neuronal release of four vasodilatory compounds, acetylcholine, vasoactive intestinal polypeptide, peptidine histidine isoleucine, and nitric oxide, i.e. a classic neurotransmitter, two neuropeptides and a gas.

Distribution of cells expressing vasoactive intestinal peptide/peptide histidine isoleucine-amide precursor messenger RNA in the rat brain

The distribution of cells expressing vasoactive intestinal peptide/peptide histidine isoleucine-amide precursor messenger RNA was investigated in the rat brain and pituitary by in situ hybridization using a synthetic 35S-labeled oligonucleotide probe. Detection of labeled neurons by light-microscopic radioautography revealed a selective repartition of the messenger RNA-expressing cells. Several major vasoactive intestinal peptide/peptide histidine isoleucine-amide messenger RNA-containing cell groups were demonstrated including layers II-VI of the cerebral cortex, the suprachiasmatic nucleus and various thalamic structures such as the ventrolateral, posterior, lateral reticular, paracentralis and gelatinosus nuclei. Positive cells, to a lesser extent, were also found in the limbic system, medial preoptic area, superior and inferior colliculi as well as in the central gray matter. They were totally absent in the pituitary and the pineal gland of normal rats. The results of the present study provide a detailed mapping of neurons expressing vasoactive intestinal peptide/peptide histidine isoleucine-amide messenger RNA in the adult rat brain. The predominance of vasoactive intestinal peptide/peptide histidine isoleucine-amide messenger RNA-containing neurons in the cerebral cortex, suprachiasmatic nucleus and thalamus suggest that vasoactive intestinal peptide is mainly involved in the control of cortical informations, circadian rhythms and sensory perception in agreement with several physiological data.

Organ distribution and characterization of porcine peptides (VIP, CGRP and PHI) that increase cAMP in rat platelets

Using an assay for rat platelet cAMP, we investigated the organ distribution of peptides that increase cAMP in rat platelets in porcine tissues. Marked activity was observed in the duodenum, pancreas and brain. By analysis with reverse phase high performance liquid chromatography (HPLC), three major peaks of activity were observed in porcine tissues. The first peak was vasoactive intestinal polypeptide (VIP), and the second peak was calcitonin gene-related peptide (CGRP). The third peak of activity was isolated from porcine duodenum. By analysis with a gas phase sequencer and with an amino acid analyzer, this peptide was identified as peptide histidine isoleucine (PHI). In a glucagon-secretin family of neuropeptides, pituitary adenylate cyclase activating polypeptide (PACAP) significantly increased platelet cAMP levels in a dose-dependent manner; however, glucagon did not. These results suggest that not only VIP and CGRP but also PHI and PACAP act upon platelets, as well as vascular tissues.

Vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM) in human penile corpus cavernosum tissue and circumflex veins: localization and in vitro effects

Localization and functional effects of vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM), two peptides derived from a common precursor molecule, were investigated in isolated preparations from human penile corpus cavernosum (CC) and circumflex vein (CV). VIP- and PHM-immunoreactivity (IR) was demonstrated in both CC and CV. The concentrations of VIP-IR and PHM-IR in CC tissue were 54.4 +/- 15.3, and 42.0 +/- 7.5 pmol g-1 wet weight respectively with a VIP/PHM ratio of 1.5 +/- 0.4 (mean +/- SEM). The corresponding values for CV tissues were 28.0 +/- 7.7 and 9.6 +/- 2.6 pmol g-1 wet weight with a VIP/PHM ratio of 3.1 +/- 0.4. CC and CV displayed VIP- and PHM-IR confined to nerve fibres in close relation to bundles of smooth muscle cells and blood vessels in both tissues. In vitro, VIP and PHM had no effects in unstimulated tissue preparations. Both peptides concentration-dependently (10(-9)-10(-6) M) relaxed CC and CV preparations precontracted with 3 x 10(-6) M noradrenaline. In CC the maximum relaxant effect of VIP and PHM was 22 +/- 11% and 9 +/- 9% and in CV the corresponding values were 82 +/- 8% and 93 +/- 3% respectively. The present study supports the hypothesis of VIP and PHM as neurotransmitters and/or neuromodulators in the nervous control of penile erection.

Prepro-vasoactive intestinal polypeptide-derived peptide sequences in cerebral blood vessels of rats: on the functional anatomy of metabolic autoregulation

This study describes the distribution of peptide sequences derived from the prepro-vasoactive intestinal polypeptide (preproVIP) molecule in perivascular nerves of rat brain arteries and arterioles. The peptides were identified by immunohistochemistry using highly specific antibodies. Five peptide sequences (preproVIP 60-76, peptide histidine isoleucine (PHI), preproVIP 111-122, VIP, and preproVIP 156-170) were identified in the perivascular nerves throughout the arterial cerebral circulation. The density of the immunoreactive fibers was highest in the nerves of the larger extracerebral arteries, declining in smaller branching arteries. All peptide sequences were identified in the nerves of small pial arterioles overlying the cortical convexity, whereas capillaries and veins contained no immunoreactive material. Dendritic processes of neocortical neurons immunoreactive for VIP and PHI could be followed towards the brain surface where the processes penetrated into the pial layer, often close to the pial vasculature. Some of the processes were also observed to enter the Virchow-Robin space, close to the arterioles. It is possible that cortical nerve cells containing VIP and PHI release the peptides in the perivascular space during periods of activity and thereby contribute to local vasodilatation associated with changes of neuronal function.

Cholecystokinin, vasoactive intestinal peptide and peptide histidine methionine responses to feeding in anorexia nervosa

Anorexia nervosa (AN) is a syndrome of unknown cause characterized by voluntary starvation. Cholecystokinin has been implicated as a neuroendocrine regulatory factor in control of satiety. Relatively little information is known about gastrointestinal hormone responses to feeding in subjects with anorexia nervosa. In the present studies, we examine fasting and postprandial levels of cholecystokinin (CCK), vasoactive intestinal peptide (VIP) and peptide histidine methionine (PHM) in anorexia nervosa subjects and in control individuals. Results of these studies indicate that plasma CCK response to a liquid meal (Ensure Plus) in untreated AN subjects was distinctly different from that observed in healthy controls, both in terms of temporal pattern of peptide released and the amount of CCK secreted into the circulation. Peak levels of CCK release occurred at 30 min following meal ingestion in AN patients and at 60 min in control subjects. Integrated CCK release in untreated AN patients was approximately twice that measured in control individuals. Renutrition therapy was associated with reversion of the pattern of CCK release to that observed in control subjects. Plasma VIP levels were unchanged following meal ingestion in both control and anorexic subjects. In contrast, PHM levels in AN subjects were significantly greater than that observed in control individuals. The pattern of PHM release following liquid meal ingestion was similar to that observed with plasma CCK; namely, peak release of peptide was observed at 30 min which was significantly greater than corresponding control values (P less than 0.05). In conclusion, these results demonstrate distinctive differences in plasma CCK and PHM levels in response to feeding in AN subjects when compared to control individuals. These findings suggest that the earlier and greater rise in plasma CCK levels in AN subjects following meal ingestion may contribute to the abnormal sensation of satiety in this condition.

Hymenolepis diminuta: changes in the levels of certain intestinal regulatory peptides in infected C57 mice

The levels of 10 regulatory peptides in acid-alcohol extracts of three regions of the small intestine (0-20%, 30-60%, and 70-100%, with respect to distance from the pylorus) have been monitored radioimmunometrically in sham-infected male (6-8 week old) C57 mice and mice given a 5-cysticercoid infection of the rat tapeworm Hymenolepis diminuta and autopsied 10 days postprimary infection and 5 days postsecondary infection (administered 28 days postprimary infection). The regulatory peptides examined were gastrin, gastrin-releasing peptide (GRP), glucagon (= enteroglucagon), motilin, neurotensin (NT), pancreatic polypeptide (PP), peptide histidine isoleucine (PHI), somatostatin (SRIF), substance P (SP), and vasoactive intestinal peptide (VIP). Statistical analyses revealed significant deviations from control values of five of the peptides (enteroglucagon and SP, both elevated; NT, PHI and VIP, all lowered) in intestinal tissue from infected mice; measurement of the same peptides in colonic extracts revealed no significant differences between infected and sham-infected mice. Parallel changes in peptide levels between normal infected and immunosuppressed infected mice were not evident, although elevations in the tissue levels of enteroglucagon and SP were found in infected Wistar rats (normal host). Results are discussed with respect to a peptidergic involvement in the pathology and host immune response to an intestinal tapeworm.

Neuropeptides of the primary sensory neurones in rat skin: an ontogenic study

Cutaneous primary sensory neurones contain a number of biologically-active peptides, including substance P (SP), neurokinin A (NKA) and calcitonin gene-related peptide (CGRP). However, little information is available on ontogenic changes in the tissue concentrations of these neuropeptides. In this study, the concentrations of these neuropeptides have been assessed in dorsal and ventral abdominal rat skin at various stages of development from foetal, early neonatal, late neonatal, weaner to adult, using sensitive and specific radioimmunoassays. In addition, the levels of peptide histidine isoleucine (PHI), a peptide found in non-sensory cutaneous nerves, were assessed to control the study. The levels of PHI and NKA immunoreactivity did not change significantly at any stage of development. However, the levels of SP and CGRP immunoreactivity were significantly elevated in the early neonate with CGRP remaining elevated in the late neonate. The levels of both SP and CGRP were not significantly different between other developmental groups. Significant elevations in cutaneous SP and CGRP concentrations in early neonatal life in the rat, at a time when the pups are blind and naked, may be related to control of cutaneous sensitivity, which during this period of development, has positive survival value for the pups.

Evidence that some preganglionic sympathetic neurons in the rat contain vasoactive intestinal peptide- or peptide histidine isoleucine amide-like immunoreactivities

Physiological studies have established that preganglionic sympathetic nerve fibers innervating the rat superior cervical ganglion release a second transmitter, in addition to acetylcholine. Based on pharmacological and histochemical investigations, possible candidates for this non-cholinergic neurotransmitter include vasoactive intestinal peptide and peptide histidine isoleucine amide. For example, previous immunohistochemical studies have demonstrated that antisera raised against both of these peptides stain neural processes in the rat preganglionic cervical sympathetic trunk and in the superior cervical ganglion. In the present study, it was found that, when the cervical sympathetic trunk was ligated, vasoactive intestinal peptide- and peptide histidine isoleucine amide-like immunoreactivities built up on both sides of the ligature. In addition, examination of the thoracic spinal cord in colchicine-treated animals revealed vasoactive intestinal peptide- and peptide histidine isoleucine amide-like immunoreactivies in neuronal cell bodies in the intermediolateral cell column and in the region of the lateral funiculus adjacent to it. In a second group of animals in which retrograde tracing techniques were used, these two regions of the spinal cord were shown to contain most of the cell bodies of the preganglionic neurons that project to the superior cervical ganglion. Smaller numbers of retrogradely labeled neurons were found dorsal to the central canal and in the nucleus intercalatus. When either vasoactive intestinal peptide- or peptide histidine isoleucine amide-like immunostaining and retrograde labeling were examined in the same animals, double-labeled neurons were found in the intermediolateral cell column and in the lateral funiculus. These data demonstrate that vasoactive intestinal peptide- and peptide histidine amide-like immunoreactivities are present in certain of the preganglionic neurons that project to the superior cervical ganglion, supporting the hypothesis that vasoactive intestinal peptide and peptide histidine isoleucine amide are released in the ganglion when these preganglionic neurons are activated.

Estrogen regulates the gene expression of vasoactive intestinal peptide in the anterior pituitary

Vasoactive intestinal peptide (VIP), a prolactin (PRL)-releasing factor, has been shown to be synthesized within the anterior pituitary. To test the hypothesis that estrogens increase PRL secretion, at least in part, by stimulating VIP secretion, the concentrations of VIP, peptide histidine isoleucine (PHI) and prepro VIP mRNA were measured in the anterior pituitaries of oophorectomized rats treated with 17 beta-estradiol benzoate 25 micrograms/kg/day s.c. for 5 days. For comparison, changes in the hypothalamus were also measured. Estrogen treatment resulted in a marked increase in pituitary VIP content without detectable changes in PHI content, suggesting that estrogen may regulate differentially the enzymes involved in the posttranslational processing of the VIP prohormone. A VIP mRNA-transcript of about 1.7 kilobases was detected in all tissues studied, being most abundant in the cortex, less abundant in the hypothalamus and barely detectable in the untreated pituitary. Estrogen treatment resulted in an increase in VIP gene expression in the pituitary but not in the hypothalamus or cerebral cortex. This marked increase in prepro VIP mRNA rendered possible the demonstration in the estrogen-treated pituitary of a second VIP transcript of about 1.0 kilobase which was present in only very low quantities in the cortex and hypothalamus. We conclude that estrogen regulates the gene expression of VIP in the anterior pituitary. Changes in VIP secretion may contribute to the stimulatory effect of estrogen on PRL secretion.

Distribution of Met-enkephalyl-Arg-Gly-Leu in rat larynx: partial coexistence with vasoactive intestinal polypeptide, peptide histidine isoleucine and neuropeptide Y

Using light microscopic (LM) enzyme-immunohistochemistry on deparaffinized adjacent sections Met-enkephalyl-Arg-Gly-Leu (ME-RGL) immunoreactivity was found to partially coexist with immunoreactive neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI) in intrinsic laryngeal neurons of the rat. Further ME-RGL-immunoreactive (ir) fibres were found around glands in the subepithelium, in connective tissue of striated muscle and in the perichondrium, as well as around arterial and venous blood vessels. They frequently contacted mast cells and macrophages. The presence of ME-RGL indicates pro-enkephalin-related origin of this novel laryngeal opioid system. From the specific target relations and close interrelations of fibres staining for opioids with those staining for the other peptides--which are known to be more or less characteristic of the sympathetic (NPY), parasympathetic (VIP, PHI) and sensory (calcitonin gene-related peptide; CGRP) subdivisions of the peripheral nervous system--we deduce that opioid/non-opioid interactions might co-control various laryngeal functions, e.g. glandular secretion, blood flow, immune and inflammatory responses and/or might be of relevance in trophic mechanisms.