vasoactive-intestinal-peptide and vasoactive-intestinal-peptide-(10-28)

A recent study reported the vasoactive intestinal peptide (VIP) fragment VIP(10-28) inhibited the rise in skin blood flow during heat stress. Our laboratory has reported that the nitric oxide (NO) pathway and histamine receptor-1 (H1)-receptor activation is common to both exogenous VIP-mediated dilation and active vasodilation (AVD). The present study aimed to further examine the specific role for VIP in AVD by using VIP(10-28) to antagonize VIP-mediated dilation in the presence of NO synthase (NOS) inhibition and an H1 antagonist. Study 1 (n = 12) examined whether VIP(10-28) antagonizes vasodilation to exogenous VIP via inhibition of NO-dependent mechanisms. Study 2 (n = 6) investigated AVD in skin sites receiving VIP(10-28) alone and in combination with NOS inhibition. Study 3 (n = 6) examined AVD in sites receiving VIP(10-28) alone and combined VIP(10-28) and H1 antagonism. Due to differences in our findings and those previously published, study 4 (n = 6) investigated whether an increase in baseline skin blood flow could result in a diminished rise in AVD. Red blood cell flux was measured using laser Doppler flowmetry, and cutaneous vascular conductance (flux/mean arterial pressure) was normalized to maximal vasodilation (28 mM sodium nitroprusside). VIP(10-28) augmented vasodilation to exogenous VIP (P < 0.05 vs. control) and hyperthermia (P < 0.05 vs. control). NOS inhibition had no effect on the augmented dilation during exogenous VIP or hyperthermia (P > 0.05). Similarly, H1-receptor antagonists had no effect on the augmented dilation during hyperthermia (P > 0.05 vs. VIP(10-28)). In study 4, percentage of maximal cutaneous vascular conductance was attenuated when baseline skin blood flow was elevated before whole body heating. Our results suggest that VIP(10-28) may be an unsuitable antagonist for examining a role for VIP-mediated dilation in human skin.

Topics: Adult; Blood Flow Velocity; Dose-Response Relationship, Drug; Female; Humans; Injections, Subcutaneous; Peptide Fragments; Skin; Skin Physiological Phenomena; Vasoactive Intestinal Peptide; Vasodilation

Active vasodilatation (AVD) in human, non-glabrous skin depends on functional cholinergic fibres but not on acetylcholine (ACh). We tested whether AVD is a redundant system in which ACh and vasoactive intestinal polypeptide (VIP) are co-released from cholinergic nerves. (1) We administered VIP by intradermal microdialysis to four discrete areas of skin in the presence of different levels of the VIP receptor antagonist, VIP(10-28), also delivered by microdialysis. Skin blood flow (SkBF) was continuously monitored by laser Doppler flowmetry (LDF). Mean arterial pressure (MAP) was measured non-invasively and cutaneous vascular conductance (CVC) calculated as LDF/MAP. Subjects were supine and wore water-perfused suits to control whole-body skin temperature (Tsk) at 34 degrees C. Concentrations of 54 microM, 107 microM, or 214 microM VIP(10-28) were perfused via intradermal microdialysis at 2 microl min-1 for approximately 1 h. Then 7.5 microM VIP was added to the perfusate containing VIP(10-28) at the three concentrations or Ringer solution and perfusion was continued for 45-60 min. At the control site, this level of VIP caused approximately the vasodilatation typical of heat stress. All VIP(10-28)-treated sites displayed an attenuated dilatation in response to the VIP. The greatest attenuation was observed at the site that received 214 microM VIP(10-28) (P < 0.01). (2) We used 214 microM VIP(10-28) alone and with the iontophoretically administered muscarinic receptor antagonist atropine (400 microA cm-2, 45 s, 10 mM) in heated subjects to test the roles of VIP and ACh in AVD. Ringer solution and 214 microM VIP(10-28) were each perfused at two sites, one of which in each case was pretreated with atropine. After 1 h of VIP(10-28) treatment, individuals underwent 45-60 min of whole-body heating (Tsk to 38.5 degrees C). VIP(10-28), alone or in combination with atropine, attenuated the increase in CVC during heat stress, suggesting an important role for VIP in AVD.

Topics: Adult; Atropine; Body Temperature Regulation; Cholinergic Fibers; Female; Heat Stress Disorders; Humans; Laser-Doppler Flowmetry; Male; Microdialysis; Parasympatholytics; Peptide Fragments; Skin; Skin Temperature; Vasoactive Intestinal Peptide; Vasodilation

The proliferation of human lymphoblastoma cell line (H9) was differently stimulated by Peptide Histidine Methionine (PHM) and Vasoactive Intestinal Peptide (VIP). PHM induced a cyclic AMP (cAMP) accumulation, abolished by Adenylate Cyclase (AC) inhibitors leading to a loss of proliferative effect. VIP mitogenic activity was Pertussis toxin (PTX) sensitive and AC inhibitors insensitive. Pharmacological experiments performed on H9 membranes with or without a GTP analogue indicated expression of both GTP-insensitive and -sensitive PHM/VIP high-affinity binding sites (HA). H9 cells expressed only the VPAC1 receptor. VIP(10-28), known as a VPAC1 antagonist, bond to all GTP-insensitive PHM sites and inhibited evenly the PHM and VIP mitogenic actions. These data strongly suggested different mechanisms initiated by VIP and PHM and highlighted the key role of GTP-insensitive binding sites in the control of cell proliferation.

Topics: Adenine; Adenylyl Cyclase Inhibitors; Analysis of Variance; Blotting, Southern; Bromodeoxyuridine; Cell Line, Tumor; Cell Proliferation; Cyclic AMP; Dose-Response Relationship, Drug; Drug Interactions; Gene Expression; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Humans; Imines; Iodine Isotopes; Lymphoma; Peptide Fragments; Peptide PHI; Pertussis Toxin; Protein Binding; Radioligand Assay; Receptors, Cell Surface; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Vasoactive Intestinal Peptide; Receptors, Vasoactive Intestinal Peptide, Type II; Receptors, Vasoactive Intestinal Polypeptide, Type I; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Time Factors; Vasoactive Intestinal Peptide

We have investigated the mechanisms underlying acute changes in gastric motor function triggered by endotoxemia. In fundal strips from rats pre-treated with endotoxin (40 microg/kg, i.p. 30 min), mechanical activity was analyzed and the source of nitric oxide (NO) was visualized by confocal microscopy of tissue loaded with the fluorescent dye DAF-FM. NOS expression was determined by quantitative RT-PCR and Western blot, and enzyme activity by the citrulline assay. Strips from endotoxin-treated rats were hypo-contractile. This was prevented by pre-incubation with the neurotoxin tetrodotoxin, the gangliar blocker hexamethonium, or non-selective and neuronal-specific NOS inhibitors (L-NOARG and TRIM, respectively). The soluble guanylyl cyclase (sGC) inhibitor ODQ and the inhibitor of small conductance Ca2+-activated K+ channels apamin prevented relaxation induced by endotoxin, nicotine, exogenous NO (DETA-NONOate), and the NO-independent sGC activator BAY 41-2272. NO synthesis was observed in neuronal soma, axons, and nerve endings of the myenteric plexus in the fundus of endotoxin-treated rats and was prevented by L-NAME, tetrodotoxin, and hexamethonium. nNOS and iNOS mRNA and protein contents were unchanged. Our findings demonstrate synthesis of NO in post-ganglionic myenteric neurons during early endotoxemia that mediates gastric hypo-contractility. The effect of NO is mediated via sGC and small conductance Ca2+-activated K+channels.

Topics: Animals; Apamin; Autonomic Fibers, Postganglionic; Carbachol; Dexamethasone; Endotoxemia; Gastric Fundus; Gastrointestinal Motility; Guanylate Cyclase; Microscopy, Confocal; Nerve Tissue Proteins; Nicotine; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Nitroarginine; Nitroso Compounds; Peptide Fragments; Potassium Channels, Calcium-Activated; Pyrazoles; Pyridines; Pyridoxal Phosphate; Rats; Suramin; Tetrodotoxin; Vasoactive Intestinal Peptide

Vasoactive intestinal peptide receptors 1 (VPAC1) and 2 (VPAC2) have been identified in humans. Cell lines expressing only VPAC1 (HT-29) or VPAC2 (Molt-4b) were identified using real-time reverse transcriptase polymerase chain reaction. Vasoactive intestinal peptide (VIP) and related peptides, VIP-6-28, VIP4-28, and VIP10-28, previously isolated from cultures of human leukocytes, were evaluated for their ability to bind to VPAC1 and VPAC2 and to increase the levels of cAMP in HT-29 and Molt-4b cells. VIP bound to membranes of HT-29 colon carcinoma cells and Molt-4b lymphoblasts with high affinity (KD = 1.6 +/- 0.2 and 1.7 +/- 0.9 nM, respectively). VIP4-28 also demonstrated high-affinity binding (KD = 1.7 +/- 0.2 and 1.7 +/- 0.7 nM in HT-29 and Molt-4b, respectively). VIP and VIP4-28 are potent VPAC1 agonists, inducing maximal 200- and 400-fold increases in cAMP, respectively. VIP demonstrated weak VPAC2 agonist activity, inducing a maximal 14-fold increase in cAMP. VIP4-28 had no VPAC2 agonist activity but demonstrated potent VPAC2 antagonist activity. VIP4-28 inhibited VPAC2-mediated increases in cAMP in Molt-4b cells up to 95%, but had no antagonistic effect on VPAC1. Lymphoblasts did not hydrolyze VIP4-28 to a form with VPAC1 antagonist activity. VIP4-28 thus is a lymphocyte-generated VIP fragment with potent agonist activity for VPAC1 and potent antagonist activity for VPAC2.

Topics: Cell Line; Dose-Response Relationship, Drug; HT29 Cells; Humans; Lymphocytes; Peptide Fragments; Peptides; Receptors, Vasoactive Intestinal Peptide; Receptors, Vasoactive Intestinal Peptide, Type II; Receptors, Vasoactive Intestinal Polypeptide, Type I; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Tumor Cells, Cultured; Vasoactive Intestinal Peptide

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

Topics: Animals; Arterioles; Biophysical Phenomena; Biophysics; Cricetinae; Mesocricetus; Micelles; Molecular Conformation; Neuropeptides; Osmolar Concentration; Peptide Fragments; Phospholipids; Pituitary Adenylate Cyclase-Activating Polypeptide; Pressure; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; Receptors, Pituitary Hormone; Receptors, Vasoactive Intestinal Peptide; Surface Tension; Vasoactive Intestinal Peptide; Vasodilator Agents; Vasomotor System

The effects of pituitary adenylate cyclase-activating peptide (PACAP-38) and vasoactive intestinal polypeptide (VIP) were investigated in the gastric fundus strips of the mouse. In carbachol (CCh) precontracted strips, in the presence of guanethidine, electrical field stimulation (EFS) elicited a fast inhibitory response that may be followed, at the highest stimulation frequencies employed, by a sustained relaxation. The fast response was abolished by the nitric oxide (NO) synthesis inhibitor L-N(G)-nitro arginine (L-NNA) or by the guanylate cyclase inhibitor (ODQ), the sustained one by alpha-chymotrypsin. alpha-Chymotrypsin also increased the amplitude of the EFS-induced fast relaxation. PACAP-38 and VIP caused tetrodotoxin-insensitive sustained relaxant responses that were both abolished by alpha-chymotrypsin. Apamin did not influence relaxant responses to EFS nor relaxation to both peptides. PACAP 6-38 abolished EFS-induced sustained relaxations, increased the amplitude of the fast ones and antagonized the smooth muscle relaxation to both PACAP-38 and VIP. VIP 10-28 and [D-p-Cl-Phe6,Leu17]-VIP did not influence the amplitude of both the fast or the sustained response to EFS nor influenced the relaxation to VIP and PACAP-38. The results indicate that in strips from mouse gastric fundus peptides, other than being responsible for EFS-induced sustained relaxation, also exerts a modulatory action on the release of the neurotransmitter responsible for the fast relaxant response, that appears to be NO.

Topics: Animals; Apamin; Carbachol; Cholinergic Agonists; Chymotrypsin; Electric Stimulation; Enzyme Inhibitors; Gastric Fundus; Guanylate Cyclase; In Vitro Techniques; Male; Mice; Mice, Inbred C57BL; Muscle Contraction; Muscle Relaxation; Neuropeptides; Neurotransmitter Agents; Nitroarginine; Oxadiazoles; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Quinoxalines; Vasoactive Intestinal Peptide

The present study was conducted to investigate the functional implication of the pituitary adenylate cyclase-activating polypeptide (PACAP) type I (PAC(1)) receptor in the adrenal catecholamine (CA) secretion induced by either PACAP-27 or vasoactive intestinal polypeptide (VIP) in anesthetized dogs. PACAP-27, VIP, and their respective antagonists were locally infused to the left adrenal gland via the left adrenolumbar artery. Plasma CA concentrations in adrenal venous and aortic blood were determined by means of a high-performance liquid chromatograph coupled with an electrochemical detector. Adrenal venous blood flow was measured by gravimetry. The administration of PACAP-27 (50 ng) resulted in a significant increase in adrenal CA output. VIP (5 microg) also increased the basal CA secretion to an extent comparable to that observed with PACAP-27. In the presence of PACAP partial sequence 6--27 [PACAP-(6--27); a PAC(1) receptor antagonist] at the doses of 7.5 and 15 microg, the CA response to PACAP-27 was attenuated by approximately 50 and approximately 95%, respectively. Although the CA secretagogue effect of VIP was blocked by approximately 85% in the presence of PACAP-(6--27) (15 microg), it remained unaffected by VIP partial sequence 10--28 [VIP-(10--28); a VIP receptor antagonist] at the dose of 15 microg. Furthermore, the CA response to PACAP-27 did not change in the presence of the same dose of VIP--(10--28). The results indicate that PACAP-(6--27) diminished, in a dose-dependent manner, the increase in adrenal CA secretion induced by PACAP-27. The results also indicate that the CA response to either PACAP-27 or VIP was selectively inhibited by PACAP-(6--27) but not by VIP-(10--28). It is concluded that PAC(1) receptor is primarily involved in the CA secretion induced by both PACAP-27 and VIP in the canine adrenal medulla in vivo.

Topics: Adrenal Medulla; Animals; Arteries; Blood Pressure; Dogs; Epinephrine; Heart Rate; Infusions, Intra-Arterial; Neuropeptides; Neurotransmitter Agents; Norepinephrine; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; Receptors, Pituitary Hormone; Regional Blood Flow; Vasoactive Intestinal Peptide

The relationship between thyrotropin-releasing hormone (TRH) binding sites and vasoactive intestinal peptide (VIP) receptors in circular muscle cells obtained from the guinea pig cecum was investigated using antagonists of VIP receptors and a selective receptor protection method. Both VIP10-28, a VIP antagonist, and atrial natriuretic peptide1-11 (ANP1-11), a VIP-specific receptor antagonist, completely inhibited 10(-5) M TRH-induced relaxation in a concentration-dependent manner. The muscle cells where cholecystokinin octapeptide (CCK-8) and TRH binding sites were protected completely preserved the inhibitory responses to TRH and ANP (a VIP-specific receptor agonist), and partially the inhibitory response to VIP. Peptide histidine isoleucine (PHI: a VIP-preferring receptor agonist) had no inhibitory effect on these cells. The muscle cells where CCK-8 and ANP (VIP-specific) receptors were protected completely preserved the inhibitory responses to TRH and ANP and partially the inhibitory response to VIP. PHI had no inhibitory effect on these cells. The muscle cells where CCK-8 and VIP receptors (both VIP-specific and VIP-preferring receptors) were protected preserved completely the inhibitory responses to TRH, VIP, ANP, and PHI. The muscle cells where CCK-8 and PHI (VIP-preferring) receptors were protected completely preserved the inhibitory response to PHI and partially the inhibitory response to VIP. TRH and ANP had no inhibitory effect on these cells. This study first demonstrates that TRH interacts with VIP-specific receptor in guinea pig cecal circular smooth muscle cells.

Topics: Animals; Atrial Natriuretic Factor; Cecum; Guinea Pigs; Male; Muscle Relaxation; Muscle, Smooth; Peptide Fragments; Receptors, Vasoactive Intestinal Peptide; Sincalide; Thyrotropin-Releasing Hormone; Vasoactive Intestinal Peptide

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.

Topics: Animals; Cats; Dose-Response Relationship, Drug; Electric Stimulation; Enzyme Inhibitors; In Vitro Techniques; Male; Muscle Relaxation; Muscle, Smooth; Neuropeptides; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Vasoactive Intestinal Peptide; Trachea; Vasoactive Intestinal Peptide

Participation of the nitric oxide-cyclic GMP pathway in nonadrenergic, noncholinergic (NANC) relaxation induced by electrical field stimulation of longitudinal muscle of the rectum of Wistar-ST rats was studied by using a selective inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). ODQ concentration dependently inhibited the relaxation and at 10 microM, maximally inhibited it by 83%. However, results obtained with N(G)-nitro-L-arginine, L-arginine and exogenously added nitric oxide excluded the participation of nitric oxide in the relaxation. An inhibitor of cyclic GMP-dependent protein kinase (PKG) partially (39%) inhibited the relaxation. ODQ also significantly inhibited the relaxation, which persisted after the PKG inhibitor-treatment, by 85%. The results strongly suggest that ODQ inhibits the NANC relaxation in a cyclic GMP-PKG pathway-independent manner.

Topics: Animals; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Enzyme Inhibitors; Guanylate Cyclase; In Vitro Techniques; Male; Muscle Relaxation; Neuropeptides; Nitroarginine; Oxadiazoles; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Quinoxalines; Rats; Rats, Wistar; Rectum; Vasoactive Intestinal Peptide

Participation of nitric oxide, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide (PACAP) in nonadrenergic, noncholinergic (NANC) relaxation of longitudinal muscle of various intestinal regions in Sprague Dawley rats (8-week-old) was studied in vitro. Nitric oxide was suggested to participate in NANC relaxation of every intestinal region studied. But the participation was partial and its extent varied among the regions: significant in the proximal colon and rectum, and moderate in the jejunum, ileum and distal colon. Participation of PACAP in NANC relaxation was suggested only in the distal colon, while that of VIP was not detected in any of regions. Results obtained in the present study indicate that extent of participation of nitric oxide in NANC relaxation in Sprague Dawley rat intestine is more significant than those of other strains, Wistar and Wistar-ST.

Topics: Animals; Atropine; Colon; Enzyme Inhibitors; Gastrointestinal Motility; Guanethidine; Ileum; Jejunum; Muscle Contraction; Muscle Relaxation; Neuropeptides; Nitric Oxide; Nitroarginine; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Rats; Rats, Sprague-Dawley; Rats, Wistar; Species Specificity; Vasoactive Intestinal Peptide

It is well known that psoriasis, an immunogenetic cutaneous disorder whose major pathogenic findings are epidermal hyperplasia and T-cell infiltration, is aggravated by psychological stresses. Although the exact mechanism is not yet clarified, antidromic secretion of neuropeptides by cutaneous nerve fibers is thought to be involved. In this study, we examined the effect and mechanism of vasoactive intestinal polypeptide (VIP), one of the major neuropeptides, on the proliferation of HaCaT cell which is a spontaneous, immortalized, human keratinocyte cell line. Twenty-four and 48 h after its addition, 1 pM to 100 nM of VIP increased the number of cells cultured with/without serum. We indirectly verified VIP(1)R on the surface of HaCaT cell based on the proliferative ability of various VIP families such as VIP, PACAP and secretin, and increased PKA level 30 min after stimulation. However, because H-89, a PKA inhibitor, did not inhibit the proliferative potential of VIP, its mitogenicity is not medicated through VIP(1)R. One nM VIP produced the TGF-alpha protein which is a strong mitogen of keratinocytes and increased in the psoriatic lesion 2.25 times more compared with the control. Genistein, a tyrosine kinase inhibitor, abrogated the mitogenic activity of VIP. Like VIP, VIP fragments, VIP(1-12) and VIP(10-28) also acted as a mitogen for HaCaT cells through the same mechanism. Collectively, our studies clearly show that VIP and its fragments stimulate keratinocyte growth, not through increased cAMP level, but through increased TGF-alpha protein production.

Topics: Cell Division; Cell Line; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; DNA; Enzyme Inhibitors; Hormone Antagonists; Humans; Isoquinolines; Keratinocytes; Mitogens; Neuropeptides; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Receptors, Cell Surface; Receptors, Vasoactive Intestinal Peptide; Receptors, Vasoactive Intestinal Polypeptide, Type I; Secretin; Sermorelin; Signal Transduction; Stress, Physiological; Sulfonamides; Transforming Growth Factor alpha; Vasoactive Intestinal Peptide

The mediators of nonadrenergic, noncholinergic (NANC) relaxation of the circular muscle of rat rectum were examined in vitro. In the circular muscle of rat rectum, NG-nitro-L-arginine (L-NOARG) at 10 microM did not affect electrical field stimulation-induced relaxation but at 100 microM it inhibited electrical field stimulation-induced relaxation by about 75% and 1-mM L-arginine reversed the inhibition. Exogenous nitric oxide (NO) (1-10 microM) concentration dependently relaxed the circular muscle. Electrical field stimulation increased the cyclic GMP content of the circular muscle to about twice its resting level. L-NOARG, even at 10 microM, completely inhibited the electrical field stimulation-induced elevation of cyclic GMP content. However, L-arginine at 1 mM did not reverse the inhibition in cyclic GMP content. Inhibitory junction potentials (i.j.ps) induced by electrical field stimulation in the circular muscle cells were not affected by L-NOARG, 100 microM. Apamin ( < or = microM) did not affect the electrical field stimulation-induced relaxation, but almost completely inhibited electrical field stimulation-induced i.j.ps. NO (0.3-10 microM) induced relaxation of the circular muscle with a concomitant decrease in intracellular Ca2+ level ([Ca2+]i). Abundant immunoreactivity of NO synthase was found in the circular muscle layer, in addition to myenteric and submucosal plexus. The results suggest that NO induces NANC relaxation with a concomitant change in [Ca2+]i in the circular muscle of rat rectum. However, the involvement of changes in cyclic GMP level and in membrane potentials in the mechanism was not shown in the present experimental conditions.

Topics: Animals; Arginine; Calcium; Cyclic GMP; Electric Stimulation; Immunohistochemistry; In Vitro Techniques; Male; Membrane Potentials; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Myenteric Plexus; Neuropeptides; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Potassium Channel Blockers; Rats; Rats, Wistar; Rectum; Vasoactive Intestinal Peptide

The effect of vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating peptide-38 (PACAP-38), and PACAP-27 on the release of serotonin (5-HT) into the intestinal lumen and the portal circulation was studied by using in vivo isolated vascularly and luminally perfused rat duodenum. 5-HT levels were determined by HPLC. VIP, PACAP-38, and PACAP-27 reduced the luminal release of 5-HT but did not affect the vascular release of 5-HT. The inhibitory effect caused by VIP, PACAP-38, and PACAP-27 was not affected by either atropine, hexamethonium, TTX, or TTX plus ACh, but it was completely antagonized by the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA). The VIP receptor antagonist VIP-(10-28) blocked the effects of VIP, PACAP-38, and PACAP-27. These results suggest that VIP and PACAP exert a direct inhibitory effect on the luminal release of 5-HT from the enterochromaffin (EC) cells via a common receptor site on the EC cells and that this effect is mediated by NO but not by cholinergic pathways. A single injection of TTX, atropine, or hexamethonium reduced the luminal release of 5-HT, whereas a single injection of VIP-(10-28) stimulated the luminal release of 5-HT and this effect was antagonized by atropine, hexamethonium, or TTX. These results suggest that EC cells may receive the direct innervation of cholinergic neurons as well as VIP and/or PACAP neurons, with the former exerting a tonic stimulatory influence and the latter exerting a tonic inhibitory influence on 5-HT release into the intestinal lumen.

Topics: Acetylcholine; Animals; Arginine; Atropine; Chromatography, High Pressure Liquid; Duodenum; Hexamethonium; Humans; In Vitro Techniques; Male; Mesenteric Arteries; Neuropeptides; Nitroarginine; Peptide Fragments; Perfusion; Pituitary Adenylate Cyclase-Activating Polypeptide; Portal Vein; Rats; Rats, Wistar; Serotonin; Swine; Tetrodotoxin; Vasoactive Intestinal Peptide

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

Topics: Anal Canal; Animals; Female; In Vitro Techniques; Isometric Contraction; Male; Muscle Relaxation; Muscle, Smooth; Neuropeptides; Neurotransmitter Agents; Nitroarginine; Opossums; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Tachyphylaxis; Vasoactive Intestinal Peptide

The circuit of myenteric interneurons that regulate excitatory input to longitudinal colonic muscle was identified using dispersed ganglia and longitudinal muscle strips with adherent myenteric plexus from rat distal colon. The preparations enabled measurement of neurotransmitter release from interneurons and/or excitatory motoneurons innervating longitudinal muscle. 1, 1-Dimethyl-4-phenylpiperizinium (DMPP) and somatostatin were used to activate myenteric neurons in dispersed ganglia and muscle strips, respectively. DMPP-stimulated vasoactive intestinal peptide (VIP) release in dispersed ganglia was inhibited by [Met]enkephalin and bicuculline and augmented by naloxone and GABA, implying that inhibitory opioid and stimulatory GABA neurons regulate the activity of VIP interneurons. In muscle strips, VIP stimulated basal and augmented somatostatin-induced substance P (SP) release; the somatostatin-induced increase in SP release was inhibited by VIP-(10-28) and NG-nitro-L-arginine, implying that excitatory VIP neurons regulate tachykinin motoneurons innervating longitudinal muscle. Somatostatin inhibited [Met]enkephalin and stimulated VIP release; basal and somatostatin-stimulated VIP release were inhibited by [Met]enkephalin and bicuculline and augmented by naloxone and GABA, implying that inhibitory pathways linking somatostatin, opioid, and GABA neurons regulate VIP interneurons, which in turn regulate tachykinin and probably cholinergic motoneurons.

Topics: Animals; Bicuculline; Colon; Dimethylphenylpiperazinium Iodide; Enkephalin, Methionine; gamma-Aminobutyric Acid; Ganglia, Autonomic; In Vitro Techniques; Interneurons; Models, Neurological; Muscle, Smooth; Myenteric Plexus; Naloxone; Neurotransmitter Agents; Nitric Oxide; Nitroarginine; Peptide Fragments; Rats; Somatostatin; Substance P; Vasoactive Intestinal Peptide

The present study sought to examine the interrelationship between nitric oxide (NO) and vasoactive intestinal peptide (VIP) in myocardial protection. Isolated rat hearts were perfused for 15 min with buffer only (Group I); 0.3 mM VIP (Group II); 3 mM L-arginine (a precursor of NO) (Group III); VIP and aminoguanidine (iNOS blocker) (Group IV); or L-arginine plus VIP 10-28 (VIP inhibitor) (Group V). Each heart was then made globally ischemic for 30 min followed by 2 h reperfusion. Both VIP and NO were found to provide cardioprotection during ischemia and reperfusion. However, the beneficial effects of VIP and NO were reduced by inhibition of NO and VIP, respectively, suggesting that cardioprotection by VIP is modulated by NO and vice versa. The results of this study suggested a coordinated regulation by cardioprotection by NO and VIP.

Topics: Animals; Arginine; Cardiotonic Agents; Enzyme Inhibitors; Guanidines; Heart; In Vitro Techniques; Models, Cardiovascular; Myocardial Ischemia; Myocardial Reperfusion; Myocardial Reperfusion Injury; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type II; Peptide Fragments; Rats; Signal Transduction; Stereoisomerism; Vasoactive Intestinal Peptide; Vasodilation

We investigated the role of capsaicin-sensitive sensory nerves (CPSNs), nitric oxide (NO), calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) in gastric adaptive and receptive relaxation in isolated guineapig stomachs. Changes in intragastric volume and pressure were recorded simultaneously in isolated stomachs in baths containing atropine and guanethidine. Adaptive relaxation was induced by luminal distention, and receptive relaxation was induced by electrical vagal stimulation. We found that desensitization to capsaicin inhibited adaptive relaxation, but not vagally induced relaxation. Extraluminal capsaicin induced gastric relaxation. Adaptive relaxation and capsaicin-induced relaxation were reduced by both tetrodotoxin and NG-nitro-L-arginine (LNNA), but not by hexamethonium. The effect of LNNA was partially reversed by co-incubation with L-arginine. Neither CGRP(8-37) nor VIP(10-28) inhibited all responses of adaptive relaxation, vagally induced and capsaicin-induced relaxation. These findings suggest that activation of CPSNs may be involved in adaptive relaxation, and that NO, but not CGRP or VIP, may be involved in the mechanisms of adaptive relaxation and receptive relaxation.

Topics: Adaptation, Physiological; Animals; Calcitonin Gene-Related Peptide; Capsaicin; Electric Stimulation; Enzyme Inhibitors; Ganglionic Blockers; Gastric Mucosa; Guinea Pigs; Hexamethonium; In Vitro Techniques; Male; Miotics; Muscle Relaxation; Muscle, Smooth; Nitric Oxide; Nitroarginine; Peptide Fragments; Stomach; Tetrodotoxin; Vagus Nerve; Vasoactive Intestinal Peptide

The purpose of this study was to begin to determine the mechanisms underlying vasodilation elicited by vasoactive intestinal peptide (VIP) in sterically stabilized liposomes (SSL) in the in situ peripheral microcirculation. Using intravital microscopy, we found that suffusion of VIP in SSL (0.42 and 0.85 nmol) onto the hamster cheek pouch for 1 h elicited significant and prolonged concentration-dependent vasodilation (P < 0.05). Suffusion of VIP in SSL (0.1 nmol) for 7 min elicited a qualitatively similar response, although its magnitude was significantly smaller than that elicited by 1 h of suffusion of VIP in SSL (P < 0.05). The VIP-receptor antagonist VIP-(10-28), but not the amino-terminal fragment VIP-(1-12), significantly attenuated and delayed the onset of VIP in SSL-induced vasodilation (P < 0.05). The nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), but not NG-nitro-D-arginine methyl ester (D-NAME), abrogated VIP in SSL-induced responses. We conclude that VIP in SSL elicits significant and prolonged vasodilation in the in situ peripheral microcirculation, which is specific, partly receptor dependent, and partly transduced by the L-arginine/NO biosynthetic pathway.

Topics: Animals; Arterioles; Cheek; Cricetinae; Dose-Response Relationship, Drug; Drug Carriers; Humans; Liposomes; Male; Mesocricetus; Microcirculation; Peptide Fragments; Phosphatidylcholines; Phosphatidylglycerols; Time Factors; Vasoactive Intestinal Peptide; Vasodilation

Capsaicin (5 x 10[-8] to 5 x 10[-5] M) produced a non-adrenergic and non-cholinergic phasic relaxation in a concentration-dependent manner in isolated dog urethral preparations precontracted by noradrenaline. The mode of action of capsaicin was investigated with special reference to the possible involvement of endogenous nitric oxide (NO). A marked tachyphylaxis was observed in the responses to capsaicin. Pretreatment with NG-nitro-L-arginine-methyl-ester (L-NAME) prevented or markedly reduced the inhibitory effect of L-NAME. Methylene blue inhibited the capsaicin-induced relaxation. In preparations stored at 4 degrees C for 72 h, the reduction in the capsaicin-induced relaxation was significantly greater than that in the relaxation induced by either electrical field stimulation or by sodium nitroprusside. We conclude that capsaicin produces an endogenous-NO-dependent relaxation in the isolated dog urethra via mechanisms that deteriorate during cold storage of the preparations.

Topics: Animals; Capsaicin; Cold Temperature; Dogs; Electric Stimulation; Female; In Vitro Techniques; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Neuropeptides; Nitric Oxide; Nitroprusside; Norepinephrine; Peptide Fragments; Urethra; Urothelium; Vasoactive Intestinal Peptide; Vasoconstrictor Agents; Vasodilator Agents

Vasoactive intestinal peptide (VIP) release, nitric oxide (NO) formation, and relaxation induced by nerve stimulation were examined in rabbit and rat gastric muscle. VIP stimulated NO formation in muscle strips, whereas NO stimulated VIP release. Nerve stimulation (0.025-16 Hz or 2-940 pulses) elicited frequency-dependent stimulation of VIP release, NO formation, and relaxation, all significant at two to three pulses. NG-nitro-L-arginine (L-NMA) abolished NO formation, abolished VIP release and relaxation at low frequencies, and partly inhibited them at higher frequencies. Oxyhemoglobin (oxy-Hb) inhibited VIP release and relaxation by 80% at low frequencies and 20-30% at higher frequencies. VIP-(10-28) abolished NO formation and relaxation at lower frequencies and partly inhibited them at higher frequencies; in contrast, VIP-(10-28) augmented VIP release in both species. The pattern of inhibition was similar in both species. Inhibition of maximal NO formation by VIP-(10-28) (82% in rabbit; 48% in rat) implied that a major component of NO is formed in muscle cells by the action of VIP. Thus 1) inhibition of relaxation by L-NNA reflects suppression of NO and VIP release from nerve terminals and NO formation in muscle cells, 2) inhibition by VIP-(10-28) partly reflects suppression of NO formation in muscle cells, and 3) inhibition by oxy-Hb reflects neutralization of extracellular NO and suppression of VIP release. The study demonstrates the dual origin of NO from nerves and muscle and its interplay with VIP in regulating relaxation.

Topics: Animals; Chemical Phenomena; Chemistry; Electric Stimulation; In Vitro Techniques; Mathematics; Muscle Relaxation; Nervous System Physiological Phenomena; Nitric Oxide; Oxyhemoglobins; Peptide Fragments; Rabbits; Rats; Stomach; Vasoactive Intestinal Peptide

We used three vasoactive intestinal polypeptide (VIP) antagonists, VIP-(10-28), [p-Cl-D-Phe6,Leu17]VIP, and NT-VIP, to evaluate the role of VIP as a mediator of vagally induced tachycardia in chloralose-anesthetized dogs. After we administered muscarinic and beta-adrenergic receptor antagonists, we evoked vagally induced tachycardia either directly, by stimulating the vagus nerves for 2 min, or reflexly, by injecting phenylephrine to increase blood pressure. Furthermore, each of the antagonists attenuated the tachycardias induced by vagal stimulation by approximately 50% and the reflexly induced tachycardias by approximately 70%. Each VIP antagonist attenuated the chronotropic responses that we evoked by injecting VIP (5.2 ng/kg) into the sinus node artery. We tested the specificity of these VIP antagonists by determining whether they attenuated the increases in heart rate evoked by two other neuropeptides [peptide histidine isoleucine (PHI) and glucagon]. VIP-(10-28) attenuated the response to PHI, but not to glucagon. The other two VIP antagonists did not alter the chronotropic responses to PHI or glucagon. Our results support the hypothesis that neurally released VIP is the principal mediator of vagally induced tachycardia in the dog.

Topics: Animals; Dogs; Female; Heart Rate; Male; Neurotensin; Peptide Fragments; Peptides; Recombinant Fusion Proteins; Tachycardia; Vagus Nerve; Vasoactive Intestinal Peptide

1. The mediators of non-adrenergic non-cholinergic (NANC) relaxation of the longitudinal muscle of rat proximal, middle and distal colon were examined in vitro. 2. Electrical transmural stimulation (TMS) of proximal, middle and distal segments of rat colon induced NANC relaxations which were inhibited by tetrodotoxin (1 microM), but not by atropine (1 microM) or guanethidine (4 microM). 3. In the proximal colon, L-nitro-arginine (N5-nitroamidino-L-2,5-diaminopentanoic acid) inhibited the TMS-induced NANC relaxation and L-arginine (1 mM) reversed this inhibition. Nitric oxide (0.3-10 microM) induced relaxation of the proximal segment. 4. NANC relaxation of the proximal segments was still evident after desensitization to vasoactive intestinal peptide (VIP). A VIP antagonist (VIP 10-28, 10 microM) had no effect on the TMS-induced NANC relaxation, which was also resistant to alpha-chymotrypsin (2 units ml-1) and a substance P antagonist ([D-Pro2, D-Trp7,9]substance P, 1 microM). 5. In the middle colon, L-nitro-arginine did not inhibit the TMS-induced NANC relaxation in 6 of 9 preparations tested and partially inhibited the relaxation in the other 3 preparations. L-Arginine did not reverse the partial inhibition. 6. Complete desensitization to VIP was not achieved in the middle colon. The VIP antagonist had no effect on the TMS-induced NANC relaxation. After alpha-chymotrypsin treatment of the segment, desensitization of the segments to substance P, or in the presence of the substance P antagonist, the TMS-induced NANC relaxation was augmented. 7. In the distal colon, L-nitro-arginine did not have any significant effect on the TMS-induced relaxation and nitric oxide did not induce relaxation. The VIP antagonist significantly inhibited TMS-induced NANC relaxation. Alpa-Chymotrypsin-treatment of the distal segments resulted in significant inhibition of NANC relaxation. No desensitization to substance P was achieved. Treatment with the substance P antagonist had no effect. 8. These results suggest that nitric oxide is the mediator of the NANC inhibitory response in the proximal region of rat colon; in the middle colon, substance P acts as an excitatory neurotransmitter, antagonizing the NANC relaxation caused by the mediator of the response, which is still uncertain. Our results suggest that that VIP is the most likely candidate as a NANC transmitter in the distal colon.

Topics: Animals; Arginine; Chymotrypsin; Colon; Electric Stimulation; Gastrointestinal Motility; In Vitro Techniques; Male; Muscle, Smooth; Neurons; Nitric Oxide; Nitroarginine; Peptide Fragments; Rats; Rats, Wistar; Substance P; Vasoactive Intestinal Peptide

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.

Topics: Animals; Binding, Competitive; Cell Separation; Cells, Cultured; Gastric Mucosa; Guinea Pigs; Muscle Relaxation; Muscle, Smooth; Peptide Fragments; Peptide PHI; Radioligand Assay; Receptors, Vasoactive Intestinal Peptide; Secretin; Stomach; Vasoactive Intestinal Peptide

Radioimmunoassays for neuroendocrine vasoactive intestinal peptide (VIP1-28) detected 30-120 fmol of structurally related peptides in extracts of 10(7) mouse peritoneal mast cells, bone marrow-derived mast cells, cultured PT-18 and C1.MC/C57.1 lines of mast cells, and rat basophilic leukemia (RBL) cells. No VIP was found in peritoneal cells of mast cell-deficient WBB6F1-W/Wv mice, whereas the amounts extracted from peritoneal cells of the congenic normal (WBB6F1-+/+) mice were similar to those from cultured mouse mast cells. Sephadex G-25 gel filtration resolved two different-sized variants of VIP from mouse mast cells and RBL cells. Amino acid sequence analyses showed that the smaller variant is VIP10-28. The principal amino-terminally larger variant of VIP from C1.MC/C57.1 mouse mast cells and RBL cells exhibited amino acid sequence homology with VIP(-6)-28, and this sequence was established for the corresponding larger VIP from PT-18 mast cells. Polymerase chain reaction amplification of two different substituent sequences of prepro VIP in RBL cell RNA identified the VIP message. VIP10-28 was released from mouse mast cells concurrently with histamine by IgE-dependent stimulation. Rodent mast cell-derived VIP thus consists of both the truncated VIP10-28 and amino-terminally larger forms that appear to be generated by peptidolysis of a preproVIP similar to that found in neural cells.

Topics: Amino Acid Sequence; Animals; Base Sequence; Cells, Cultured; Leukemia, Basophilic, Acute; Mast Cells; Mice; Mice, Inbred Strains; Molecular Sequence Data; Peptide Fragments; Protein Precursors; Radioimmunoassay; Rats; Tumor Cells, Cultured; Vasoactive Intestinal Peptide

The isolated, perfused gland was used to examine the regulation of saliva volume and protein content by vasoactive intestinal peptide (VIP). In the absence of other secretagogues, VIP produced a modest, sustained saliva flow with a biphasic dose-response curve in which saliva volume was greatest at 1 nM VIP (28.5 +/- 3.8 microliters in the first 5 min, n = 4) but reduced at lower and higher concentrations. The protein concentration in saliva released in response to VIP (0.86 +/- 0.13 micrograms/microliters) was substantially higher than with 30 nM acetylcholine (0.06 +/- 0.02 micrograms/microliters) or 1 nM substance P (0.30 +/- 0.05 micrograms/microliters). During the first 5 min of stimulation, VIP and substance P were synergistic in terms of volume and protein content whereas inclusion of VIP did not increase acetylcholine-stimulated flow in the first 5 min but produced a higher sustained flow over the next hour. After stimulation with acetylcholine, subsequent addition of VIP transiently enhanced saliva volume and protein content in a monophasic, dose-dependent manner with effects at 1 pM VIP and higher. The responses were different for VIP compared with other cAMP-mobilizing agents and the involvement of multiple VIP receptor subtypes was suggested from experiments in which a VIP antagonist blocked the VIP enhancement of saliva volume but not the increase in protein.

Topics: Acetylcholine; Alprostadil; Animals; Chemotherapy, Cancer, Regional Perfusion; Colforsin; Cyclic AMP; Dose-Response Relationship, Drug; Isoproterenol; Male; Peptide Fragments; Rats; Rats, Inbred Strains; Saliva; Salivary Proteins and Peptides; Secretory Rate; Submandibular Gland; Substance P; Vasoactive Intestinal Peptide

The role of vasoactive intestinal peptide (VIP) in neurally mediated relaxation of guinea pig and rat intestine was examined with three putative VIP antagonists: a C-terminal sequence of VIP (VIP10-28), substituted analogs of VIP ([4-Cl-D-Phe6, Leu17]VIP) and growth hormone releasing factor (GRF) ([Ac-Tyr1, D-Phe2] GRF1-29). The three agents inhibited selectively relaxation induced by VIP and its homolog, peptide histidine isoleucine. Inhibition of VIP-induced relaxation in tenia coli and gastric fundic strips was consistent with competitive antagonism. Relaxation induced by field stimulation (80 V; 1 msec; 0.1-16 Hz) which is accompanied by a stoichiometric increase in VIP release was inhibited by the three antagonists in the following order of potency: VIP10-28 greater than VIP analog greater than GRF analog. The descending relaxation component of the peristaltic reflex induced by graded stretch of the orad end of a rat colonic segment which is also accompanied by an increase in VIP release, was inhibited by the three VIP antagonists in the same order of potency: VIP10-28 greater than VIP analog greater than GRF analog. The most potent antagonist, VIP10-28, abolished descending relaxation at the lowest grades of stretch (2 and 4 g) and inhibited relaxation at the highest grades of stretch (10 g) by 79%. The results indicate that VIP (and peptide histidine isoleucine) is the transmitter responsible for neurally induced gastric and intestinal relaxation.

Topics: Animals; Electric Stimulation; Growth Hormone-Releasing Hormone; Guinea Pigs; In Vitro Techniques; Motor Neurons; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Peptide Fragments; Rats; Vasoactive Intestinal Peptide

Blockade of electrical activity in dissociated spinal cord cultures results in a significant loss of neurons during a critical period in development. Decreases in neuronal cell numbers and 125I-labeled tetanus toxin fixation produced by electrical blockade with tetrodotoxin (TTX) were prevented by addition of vasoactive intestinal peptide (VIP) to the nutrient medium. The most effective concentration of VIP was 0.1 nM. At higher concentrations, the survival-enhancing effect of VIP on TTX-treated cultures was attenuated. Addition of the peptide alone had no significant effect on neuronal cell counts or tetanus toxin fixation. With the same experimental conditions, two closely related peptides, PHI-27 (peptide, histidylisoleucine amide) and secretin, were found not to increase the number of neurons in TTX-treated cultures. Interference with VIP action by VIP antiserum resulted in neuronal losses that were not significantly different from those observed after TTX treatment. VIP10-28, a fragment that inhibits VIP stimulation of adenylate cyclase, also produced a dose-dependent decrease in neuronal cell counts similar to that seen with TTX treatment. These data indicate that under conditions of electrical blockade a neurotrophic action of VIP on neuronal survival can be demonstrated.

Topics: Adenylyl Cyclases; Animals; Cell Count; Cell Survival; Cells, Cultured; Dose-Response Relationship, Drug; Drug Interactions; Electrophysiology; Enzyme Activation; Mice; Mice, Inbred C57BL; Neural Inhibition; Neurons; Peptide Fragments; Spinal Cord; Tetanus Toxin; Tetrodotoxin; Vasoactive Intestinal Peptide