Pharmacological characterization and expression of VIP and PACAP receptors in isolated cranial arteries of the rat

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide (PACAP) are potent vasodilators in animals and humans. PACAP infusion but not VIP infusion precipitates migraine attacks in migraine patients. The vascular effects of VIP and the two varieties of PACAP (PACAP-27 and PACAP-38) were investigated versus selective antagonists in segments of rat middle cerebral arteries (MCA), basilar arteries (BA) and middle meningeal arteries (MMA) using myographs. The luminal and abluminal effects of VIP were studied using perfusion myograph. mRNA expression of the relevant receptors (VPAC₁, VPAC₂ and PAC₁) was examined by in situ hybridization. There was no significant difference in relaxant potency of the peptides in the MCA. In BA the relaxant potency was VIP > PACAP-27 = PACAP-38. Relaxant responses were either absent or very weak in MMA. VIP was found to be somewhat more potent in BA than in the MCA. Maxadilan, a selective PAC₁-receptor agonist, showed no relaxant effect in either vessel. The VPAC₂-antagonist PG 99-465 alone proved ineffective in the MCA, while it had a weak effect on BA. The VPAC₁-antagonist PG 97-269 inhibited relaxation induced by both VIP and the PACAPs in cerebral vessels. In combination, the two antagonists demonstrated better effect than either alone. VIP applied luminally via perfusion myograph caused no dilatation, indicating lack of endothelial involvement. In situ hybridization demonstrated the presence of mRNA for all three receptors in the smooth muscle cells of the vessels. In conclusion, migraine-like headache induced by PACAP-38 infusion is unlikely to be caused by direct vasodilator action on intracranial vessels.     

Neuronal and smooth muscle receptors involved in the PACAP- and VIP-induced relaxations of the pig urinary bladder neck

BACKGROUND AND PURPOSE: As pituitary adenylate cyclase-activating polypeptide 38 (PACAP 38)- and vasoactive intestinal peptide (VIP) are widely distributed in the urinary tract, the current study investigated the receptors and mechanisms involved in relaxations induced by these peptides in the pig bladder neck. EXPERIMENTAL APPROACH: Urothelium-denuded strips were suspended in organ baths for isometric force recordings and the relaxations to VIP and PACAP analogues were investigated. KEY RESULTS: VIP, PACAP 38, PACAP 27 and [Ala(11,22,28)]-VIP produced similar relaxations. Inhibition of neuronal voltage-gated Ca(2+) channels reduced relaxations to PACAP 38 and increased those induced by VIP. Blockade of capsaicin-sensitive primary afferents (CSPA), nitric oxide (NO)-synthase or guanylate cyclase reduced the PACAP 38 relaxations but failed to modify the VIP responses. Inhibition of VIP/PACAP receptors and of voltage-gated K(+) channels reduced PACAP 38 and VIP relaxations, which were not modified by the K(+) channel blockers iberiotoxin, charybdotoxin, apamin or glibenclamide. The phosphodiesterase 4 inhibitor rolipram and the adenylate cyclase activator forskolin produced potent relaxations. Blockade of protein kinase A (PKA) reduced PACAP 38- and VIP-induced relaxations. CONCLUSIONS AND IMPLICATIONS: PACAP 38 and VIP relax the pig urinary bladder neck through muscle VPAC(2) receptors linked to the cAMP-PKA pathway and involve activation of voltage-gated K(+) channels. Facilitatory PAC(1) receptors located at CSPA and coupled to NO release, and inhibitory VPAC receptors at motor endings are also involved in the relaxations to PACAP 38 and VIP, respectively. VIP/PACAP receptor antagonists could be useful in the therapy of urinary incontinence produced by intrinsic sphincter deficiency.     

Receptor occupancy and adenylate cyclase activation in AR 4-2J rat pancreatic acinar cell membranes by analogs of pituitary adenylate cyclase-activating peptides amino-terminally shortened or modified at position 1, 2, 3, 20, or 21.

In AR 4-2J rat pancreatic acinar cell membranes, receptors for the two pituitary adenylate cyclase-activating peptides (PACAP) PACAP-27 (the short version of PACAP) and PACAP-38 [the long version, with a carboxyl-terminal (residues 28-38) extension] can be subdivided into (a) type A receptors, with high affinity (Kd, 0.3-0.5 nM) for both PACAP-27 and PACAP-38, and (b) type B receptors, with high affinity for PACAP-38 (Kd, 0.3 nM) but low affinity for PACAP-27 (Kd, 20 nM). Determinants of agonist/antagonist activity in 47 PACAP-27 and PACAP-38 analogs (mono- or disubstituted in positions 1, 2, 3, 20, and 21) or amino-terminally shortened were tested by (a) the occupancy of PACAP-A receptors, preferentially labeled with [125I-N-acetyl-His1]PACAP-27, and that of PACAP-A and -B receptors, both labeled with 125I-PACAP-38, and (b) the resulting activation or inhibition of adenylate cyclase. For PACAP-A receptor recognition, deprotonated His1 was a major determinant for PACAP-27 but not PACAP-38; the Kd of 125I-PACAP-27 decreased 2.4-fold at 37 degrees between pH 6.0 and 7.5 and 3.6-fold at 15 degrees, whereas the IC50 of [N-acetyl-His1]PACAP-27 was less affected and that of PACAP(2-27), PACAP(2-38), and PACAP(1-38) was pH independent. In addition, PACAP-A receptors coupled to adenylate cyclase were much more sensitive to PACAP-38 derivatives than to PACAP-27 derivatives; for instance, [D-Phe2]PACAP-38 was a more potent antagonist (Ki, 5 nM) than [D-Phe2]PACAP-27 (Ki, 350 nM), and PACAP(6-38) was a more potent antagonist (Ki, 7 nM) than PACAP(6-27) (Ki, 300 nM). PACAP-B receptors, apart from showing high affinity for PACAP-38, displayed relatively high affinity for amino-terminally shortened PACAP-38 fragments and poor affinity for PACAP-27 and PACAP-27 fragments.     

Pharmacological properties of two recombinant splice variants of the PACAP type I receptor,transfected and stably expressed in CHO cells

Two splice variants of the pituitary adenylate cyclase activating polypeptide (PACAP) type I receptor (PACAP receptor and PACAP/HOP receptor isoform) were stably expressed in Chinese hamster ovary (CHO) cells that did not express constitutively receptors for this family. The PACAP./HOP receptor protein had a 28 amino acis extension in the C-terminal part of the third intracellular loop. The two cell lines studied, CHO 2–10 (PACAP receptor) and CHO 4–12 (PACAP/HOP receptor) expressed a receptor density of 4.6±0.3 and 2.6±0.2 pmol/mg protein, respectively, with corresponding K_d values of 14.2±2.0 and 8.2±1.0 nM for [Ac-His¹]PACAP-27 used as a tracer. Tracer binding was slightly decreased by GTP in both clones. The K_d values of PACAP-27, PACAP-38, vasoactive intestinal peptide (VIP), PACAP-27 fragments and analogues evaluated by binding competition curves, were higher in CHO 2–10 than in CHO 4–12, whereas the K_d for PACAP-38 fragments did not differ. The receptors were coupled to adenylate cyclase and the EC₅₀ values were lower than the K_d values in both cell lines, suggesting an amplification process due to the existence of spare receptors. Pretreatment of the CHO 4–12 cells with increasing concentrations of PACAP-27 for 24 h induced an increase in the K_act values and a decrease in the maximal stimulation; the same pretreatment of CHO 2–10 cells also induced an increase in the K_act values, but a marked increase in the adenylate cyclase activity in the absence of added peptide, suggesting that PACAP pretreatment had induced a permanent coupling of the receptor to the G_s site. Thus, the two splice variants differed in their capacity to recognize the ligand, and in their coupling to the G_s sites.     

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

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

Pituitary adenylate cyclase activating peptide mediates inhibitory nonadrenergic noncholinergic relaxation

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

Pituitary adenylate cyclase activating peptide,a novel VIP-like gut-brain peptide,relaxes the guinea-pig taenia caeci via apamin-sensitive potassium channels

Summary Effects of pituitary adenylate cyclase activating peptide (PACAP-(1-27)) and vasoactive intestinal polypeptide (VIP) on the guinea-pig taenia caeci were studied in the presence of guanethidine and scopolamine. Both peptides (1 nmol/1-1 mol/1) concentration-dependently relaxed the smooth muscle of the taenia. PACAP-(1-27) and VIP were nearly equipotent. Apamin (30 nmol/1), a selective blocker of calcium-activated potassium channels, abolished the relaxation induced by PACAP-(1–27) whereas the effect of VIP remained unaffected. PACAP-(1–27) may be a candidate for the noncholinergic, non-adrenergic inhibitory neurotransmitter which induces apamin-sensitive relaxation in the intestinal tract. Correspondence to H. Schwörer at the above address     

Vasoactive intestinal peptide receptor antagonists in rat seminal vesicle membranes.

Vasoactive intestinal peptide (VIP) receptors coupled to activation of adenylate cyclase have been previously identified in seminal vesicle membranes of rat. In the present study we demonstrate that the synthetic peptides [4-Cl-D-Phe6,Leu17]VIP and the growth hormone releasing factor (GRF) analog [Ac-Tyr1,D-Phe2]GRF1-29-NH2 inhibit in a competitive manner the specific 125I-VIP binding to the same membrane preparation. The order of potency of the two peptides compared to VIP was: VIP (IC50 = 1.3 +/- 0.5 nM) greater than [4-Cl-D-Phe6,Leu17]VIP(IC50 = 1600 +/- 45.0 nM) greater than [Ac-Tyr1,D-Phe2]GRF1-29-NH2(IC50 = 290.0 +/- 59.4 nM). Whereas VIP showed a stimulatory activity upon adenylate cyclase with a potency (ED50 = 7.0 +/- 0.7 nM) compatible with the affinity of the VIP binding sites previously described, the other two peptides tested showed no effect at that level. The behavior as antagonists of both [4-Cl-D-Phe6,Leu17]VIP and [Ac-Tyr1,D-Phe2]GRF1-29-NH2 was confirmed by: (a) the parallel shifts of the VIP dose-response curves for stimulation of adenylate cyclase activity in the presence of the antagonists; (b) the close agreement between the binding affinity and the inhibition of adenylate cyclase activity for the two peptides; and (c) the lack of effect of the two antagonists upon the adenylate cyclase activity stimulated by the beta-adrenoceptor agonist isoproterenol which indicates the specificity of the interaction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution and effects of pituitary adenylate cyclase activating peptide in cat and human lower oesophageal sphincter.

1. The localization, tissue concentrations, and effects of pituitary adenylate cyclase activating peptide (PACAP) 27 and 38 were investigated in cat and human lower oesophageal sphincter (LOS), and compared with those of vasoactive intestinal peptide (VIP) and helospectin. 2. PACAP-immunoreactive nerve structures were found in the cat and human LOS, with an abundance in the circular smooth muscle layer. PACAP 27-immunoreactivity was often co-localized with VIP-immunoreactivity. 3. In cat tissue, PACAP (PACAP 27 plus PACAP 38) concentrations were 50 fold lower than VIP concentrations; in human tissue they were 10 fold lower. 4. PACAP 27, PACAP 38, helospectin I, and VIP induced concentration-dependent relaxations in circular smooth muscle preparations from cat and human LOS. The order of potency was: VIP > helospectin I > or = PACAP 27 > PACAP 38. NG-nitro-L-arginine, scopolamine, or apamin, did not influence the relaxant effects of PACAP 27 or VIP. 5. In cat preparations, both cyclic AMP and cyclic GMP levels were increased after exposure to PACAP 27 and helospectin I, whereas exposure to VIP was followed by an increase in cyclic AMP levels only. In human preparations, there was an increase in cyclic AMP levels without any change in cyclic GMP levels. 6. These results suggest that in the cat and human LOS, PACAP 27 and VIP can occur within the same nerve structures. PACAP 27 has a potent relaxant action, but its functional importance has to be established.     

Heterogeneity of neuronal and smooth muscle receptors involved in the VIP- and PACAP-induced relaxations of the pig intravesical ureter

1. The mechanisms and receptors involved in the vasoactive intestinal peptide (VIP)- and pituitary adenylate cyclase-activating polypeptide (PACAP)-induced relaxations of the pig intravesical ureter were investigated. 2. VIP, PACAP 38 and PACAP 27 concentration-dependently relaxed U46619-contracted ureteral strips with a similar potency. [Ala(11,22,28)]-VIP, a VPAC(1) agonist, showed inconsistent relaxations. 3. The neuronal voltage-gated Ca(2+) channel inhibitor, omega-conotoxin GVIA (omega-CgTX, 1 microm), reduced the VIP relaxations. Urothelium removal or blockade of capsaicin-sensitive primary afferents, nitric oxide (NO) synthase and guanylate cyclase with capsaicin (10 microm), N(G)-nitro-l-arginine (l-NOARG, 100 microm) and 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 5 microm), respectively, did not change the VIP relaxations. However, the PACAP 38 relaxations were reduced by omega-CgTX, capsaicin, l-NOARG and ODQ. 4. The VIP and VIP/PACAP receptor antagonists, [Lys(1), Pro(2,5), Arg(3,4), Tyr(6)]-VIP (1 microm) and PACAP (6-38) (0.4 microm), inhibited VIP and VIP and PACAP 38, respectively, relaxations. 5. The nonselective and large-conductance Ca(2)-activated K(+) channel blockers, tetraethylammonium (3 mm) and charybdotoxin (0.1 microm), respectively, and neuropeptide Y (0.1 microm) did not modify the VIP relaxations. The small-conductance Ca(2)-activated K(+) channel blocker apamin (1 microm) did not change the PACAP 27 relaxations. 6. The cAMP-dependent protein kinase A (PKA) blocker, 8-(4-chlorophenylthio)adenosine-3',5'-cyclic monophosphorothioate (Rp-8-CPT-cAMPS, 100 microm), reduced VIP relaxations. The phosphodiesterase 4 inhibitor rolipram and the adenylate cyclase activator forskolin relaxed ureteral preparations. The rolipram relaxations were reduced by Rp-8-CPT-cAMPS. Forskolin (30 nm) evoked a potentiation of VIP relaxations. 7. These results suggest that VIP and PACAP relax the pig ureter through smooth muscle receptors, probably of the VPAC(2) subtype, linked to a cAMP-PKA pathway. Neuronal VPAC receptors localized at motor nerves and PAC(1) receptors placed at sensory nerves and coupled to NO release, seem also to be involved in the VIP and PACAP 38 relaxations.     

Tritium labelling of PACAP‐38 using a synthetic diiodinated precursor peptide

In the interest of developing efficient methods for tritium labelling peptides, we here demonstrate the successful labelling of PACAP‐38 (pituitary adenylate cyclase‐activating polypeptide), a 38‐mer peptide, using a synthetic diiodinated PACAP‐38 precursor. In this example, we employ standard hydrogenation chemistry with the use of a heterogeneous palladium catalyst and carrier‐free tritium gas on a tritium manifold system. Copyright © 2011 John Wiley & Sons, Ltd.     

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in the goose cerebral cortex

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in the goose cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [(125)I]-VIP, and (2) effects of peptides from the VIP/PACAP/secretin family on cyclic AMP formation. The binding of [(125)I]-VIP to goose cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of receptor binding sites with a high affinity (K(d)=0.76 +/- 0.13 nM) and high capacity (B(max)=70 +/- 7 fmol/mg of protein). Various peptides displaced the specific binding of 0.12 nM [(125)I]-VIP to the goose cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [(125)I]-VIP binding to the goose cerebrum was: PACAP(38) asymptotically equal to mammalian VIP > or = PACAP(27) asymptotically equal to chicken VIP > PHI (peptide histidine-isoleucine) > secretin (inactive). About 52% of specific [(125)I]-VIP binding sites in the goose cerebral cortex was sensitive to 5'-guanylimidodiphosphate [Gpp(NH)p], a nonhydrolyzable analogue of GTP. PACAP(38) and PACAP(27) potently stimulated cyclic AMP formation in the goose cerebral cortical slices in a concentration-dependent manner, displaying EC(50) values of 45.5 nM and 51.5 nM, respectively. Chicken VIP was markedly less potent than both forms of PACAP, mammalian VIP only weakly affected the nucleotide production, while effects evoked by PHI were negligible. It is concluded that the cerebral cortex of goose contains VPAC type receptors that are labeled with [(125)I]-VIP and are positively linked to cyclic AMP formation. In addition, the observed stronger action of PACAP, when compared to VIP, on cyclic AMP production in this tissue suggests its interaction with both PAC(1) and VPAC receptors.     

Pharmacological properties of Chinese hamster ovary cells coexpressing two vasoactive intestinal peptide receptors (hVPAC1 and hVPAC2)

1. In the light of recent findings that VPAC1 and VPAC2 receptors form homodimers and heterodimers, we have evaluated the function of these receptors coexpressed in the same cells, using whole-cell and membrane preparations. Cells expressing each receptor alone were used for comparison. 2. The study was performed on Chinese hamster ovary cells stably transfected with both human recombinant receptors and we compared receptor occupancy and adenylate cyclase activation by VIP, Ro 25-1553 - a VPAC2 selective agonist - and [K(15),R(16),L(27)]VIP(1-7)/GRF(8-27) - a VPAC1 selective agonist - on membranes prepared from each cell line and on a mixture of membranes from cells expressing each receptor individually. We also studied receptor internalization induced by the three agonists on intact cells expressing both receptors alone or together by fluorescence-activated cell sorting using monoclonal antibodies and demonstrated by using co-immunoprecipitation that the two receptors did interact.3. The results indicated that coexpression of the receptors did not modify the recognition of ligands, nor the capacity of the agonists to stimulate adenylate cyclase activity and, in intact cells, to induce internalization of the receptors.4. As a consequence, the properties of the selective ligands that were established on cell lines expressing a single population of VIP receptors were valid on cells expressing both receptors. Furthermore, the recently demonstrated VPAC1/VPAC2 receptor heterodimerization did not affect the function of either receptor.     

Pituitary adenylate cyclase-activating polypeptide: a novel, long-lasting, endothelium-independent vasorelaxant

The vasoactivity of the 27- and 38-amino acid forms of the novel peptide pituitary adenylate cyclase-activating polypeptide (PACAP) was tested in vitro. Both forms of PACAP caused endothelium-independent vasodilation (assayed by their vasodilator action on rabbit aorta). When superfused for 1 min the relaxation EC50 of PACAP27 was 23 +/- 8 nM and of PACAP38 was 152 +/- 66 nM. PACAP was 100-fold more potent than vasoactive intestinal polypeptide (VIP) (PACAP27 shows 68% amino acid sequence homology with VIP), and had a prolonged duration of action, a 1 min exposure to 1 microM PACAP27 lasting 135 +/- 7 min and to 1 microM PACAP38 108 +/- 3 min. Adenylate cyclase activity in homogenates of rabbit aortic smooth muscle cells was increased by PACAP27 and PACAP38 with EC50s of 4.4 and 0.73 nM, respectively. PACAP27 and PACAP38 are potent, long-lasting, endothelium-independent vasodilators.     

Electrical and mechanical effects of vasoactive intestinal peptide and pituitary adenylate cyclase-activating peptide in the rat colon involve different mechanisms

This work aimed to study the effects of pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) on the mechanical and electrical activity of the circular muscle of the rat colon and the mechanisms involved in such effects. Spontaneous mechanical activity was studied in vitro in an organ bath and the membrane potential was recorded using the microelectrode technique. Both VIP and PACAP (0.1 microM) caused an immediate, sustained and tetrodotoxin (1 microM)-resistant inhibition of the cyclic spontaneous mechanical activity and hyperpolarization. The small-conductance Ca(2+)-activated K(+) channel blocker, apamin (1 microM), did not change the VIP- and PACAP-induced relaxation but reduced the hyperpolarization induced by PACAP whereas it did not change that induced by VIP. In contrast, the purinoceptor antagonist, suramin (100 microM), blocked the hyperpolarization caused by PACAP and VIP but failed to change their mechanical inhibitory effects. Moreover, the putative PACAP and VIP receptor antagonists, PACAP-(6-38) and VIP-(10-28), respectively, both 3 microM, failed to change the effects of either peptide and modified neither the inhibitory junction potential nor the relaxation induced by electrical-field stimulation. Thus, these results suggest that the mechanisms mediating relaxation are not strictly coupled to the mechanisms mediating hyperpolarization. This could be due to activation of two distinct mechanisms of action after agonist receptor interaction.     

Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a superfamily of structurally related peptide hormones that includes glucagon, glucagon-like peptides, secretin, gastric inhibitory peptide (GIP) and growth hormone-releasing hormone (GHRH). VIP and PACAP exert their actions through three GPCRs – PAC₁, VPAC₁ and VPAC₂– belonging to class B (also referred to as class II, or secretin receptor-like GPCRs). This family comprises receptors for all peptides structurally related to VIP and PACAP, and also receptors for parathyroid hormone, corticotropin-releasing factor, calcitonin and related peptides. PAC₁ receptors are selective for PACAP, whereas VPAC₁ and VPAC₂ respond to both VIP and PACAP with high affinity. VIP and PACAP play diverse and important roles in the CNS, with functions in the control of circadian rhythms, learning and memory, anxiety and responses to stress and brain injury. Recent genetic studies also implicate the VPAC₂ receptor in susceptibility to schizophrenia and the PAC₁ receptor in post-traumatic stress disorder. In the periphery, VIP and PACAP play important roles in the control of immunity and inflammation, the control of pancreatic insulin secretion, the release of catecholamines from the adrenal medulla and as co-transmitters in autonomic and sensory neurons. This article, written by members of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) subcommittee on receptors for VIP and PACAP, confirms the existing nomenclature for these receptors and reviews our current understanding of their structure, pharmacology and functions and their likely physiological roles in health and disease. More detailed information has been incorporated into newly revised pages in the IUPHAR database (http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=67).

LINKED ARTICLES

This article is part of a themed section on Secretin Family (Class B) G Protein-Coupled Receptors. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-1     

Interplay between PACAP and NO in mouse ileum

We investigated the possibility that pituitary adenylate cyclase activating peptide (PACAP) has a role in the control of contractility in the mouse ileum. PACAP-(1-27) produced tetrodotoxin (TTX)-insensitive, concentration-dependent reduction of the amplitude of the spontaneous contractions of longitudinal muscle up to their complete disappearance. This effect was inhibited by PACAP-(6-38), PACAP receptor antagonist, and by apamin, blocker of small-conductance Ca2+-activated K+-channels. Nomega-nitro-L-arginine methyl ester (L-NAME), nitric oxide (NO) synthase inhibitor, reduced the PACAP-inhibitory response, and the joint application of apamin plus L-NAME produced additive effects. 1H-[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), inhibitor of NO-stimulated soluble guanylate cyclase, significantly reduced the effect of PACAP. Exogenous NO, given as sodium nitroprusside (SNP), induced a concentration-dependent suppression of the phasic contractions, which was unaffected by apamin but reduced by either PACAP-(6-38) or TTX. Neurally evoked muscular relaxation was deeply antagonised by L-NAME. PACAP-(6-38) induced a reduction of the response to EFS only in the absence L-NAME. In conclusion, our results suggest that PACAP controls smooth muscle contractility, acting directly on the muscle cells through PACAP-27 preferring receptors coupled to apamin-sensitive Ca2+-dependent K+-channels and indirectly through the stimulation of NO production. In turn, NO would stimulate the release of PACAP from inhibitory neurones.     

Effects of neuropeptides of the secretin/VIP/PACAP family on cyclic AMP formation in the chick hypothalamus and cerebral cortex

Six neuropeptides: short and long form of the pituitary adenylate cyclase activating polypeptide (PACAP), i.e. PACAP27 and PACAP38, vasoactive intestinal peptide (VIP), peptide histidine-isoleucine (PHI), secretin and glucagon, members of the secretin/VIP/PACAP superfamily ofpolypeptides, were tested for their ability to stimulate cyclic AMP formation in [3H]adenine-prelabeled slices of the chick hypothalamus and cerebral cortex. Of the tested peptides, only PACAP evoked pronounced and significant responses in the two analyzed brain structures. Although magnitude of the responses varied in different experiments, the effects of both forms of PACAP were usually larger in the cerebral cortex than in the hypothalamus. Glucagon, PHI (both used at concentrations 0.01-1 microM) and VIP (0.1-3 microM) induced concentration-dependent yet comparatively small effects that did not reach statistical significance, while secretin (0.1-3 microM) had no effect.     

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) activate protein kinase C in chick cerebral cortex

Pituitary adenylate cyclase-activating polypeptide (PACAP38) and vasoactive intestinal peptide (VIP) were tested for their ability to influence protein kinase C (PKC) activity in the chick cerebral cortical slices. Thirty minutes incubation of the chick tissue with PACAP38 (0.1-1 microM) or VIP (0.3-3 microM) produced significant and concentration-dependent changes in PKC activity. Both peptides enhanced the enzyme activity in cell membrane preparation, and decreased it in cytosol preparation obtained from cerebral cortical slices. These changes in PKC activity suggest that PACAP and VIP are capable of activating this enzyme in cerebral cortex of chick.     

β<Superscript>2</Superscript>/β<Superscript>3</Superscript>-di- and α/β<Superscript>3</Superscript>-tetrapeptide derivatives as potent agonists at somatostatin sst<Subscript>4</Subscript> receptors

Four linear beta(2)/beta(3)-di- and alpha/beta(3)-tetrapeptides (1-4) were investigated as somatostatin sst(4) receptor agonists on recombinant human and mouse somatostatin receptors. Human somatostatin receptor subtypes 1-5 (sst(1-5)), and mouse somatostatin receptor subtypes 1,3,4 and 5, were characterised using the agonist radioligands [(125)I]LTT-SRIF-28, [(125)I][Tyr(10)]CST(14) and [(125)I]CGP 23996 in stably transfected Chinese hamster lung fibroblast (CCL39) cells. The peptides bound selectively to sst(4) receptors with nanomolar affinity (pK(d)=5.4-7.8). The peptides were investigated on second messenger systems both as agonists, and as antagonists to SRIF-14-mediated effects in CCL39 cells expressing mouse sst(4 )receptors, via measurement of inhibition of forskolin-stimulated adenylate cyclase activity, and stimulation of luciferase expression. The peptides showed full agonism or pronounced partial agonism (40 to 100% relative intrinsic activity) in both inhibition of forskolin-stimulated adenylate cyclase activity (pEC(50)=5.5-6.8), and luciferase expression (pEC(50)=5.5-6.5). The agonist potential was confirmed since antagonism was very difficult to establish. The data show that beta(2)/beta(3)-di- and alpha/beta(3)-tetrapeptide derivatives have agonist potential at recombinant somatostatin sst(4) receptors. Therefore, they may be used to elucidate physiological and biochemical effects mediated by sst(4), and may also have potential as therapeutic agents.