Dysfunction of the gastrointestinal tract. Vasoactive intestinal peptide in peristalsis and sphincter function

Zhizhu decoction alleviates slow transit constipation by regulating aryl hydrocarbon receptor through gut microbiota

CONTEXT

Slow transit constipation (STC), the most common type of constipation, seriously affects the life of patients. Zhizhu decoction (ZZD), a traditional Chinese medicine compound, has is effective against functional constipation, but the mechanism is still unclear.

OBJECTIVE

This research explores the mechanism of ZZD on STC from the perspective of metabolomics and gut microbiota.

MATERIALS AND METHODS

Fifty-four C57BL/6 mice were randomly divided into six groups (n = 9): control (control); STC (model); positive control (positive); low-dose (5 g/kg; L-ZZD), medium-dose (10 g/kg; M-ZZD), and high-dose (20 g/kg; H-ZZD) ZZD treatment. Following treatment of mice with ZZD for two weeks, the changes in intestinal motility, colon histology, intestinal neurotransmitters, and aryl hydrocarbon receptor (AHR) pathway determined the effects of ZZD on the pathophysiology of STC. LC-MS targeting serum metabolomics was used to analyze the regulation of ZZD on neurotransmitters, and 16S rRNA high-throughput sequencing was used to detect the regulation of the gut microbiome.

RESULTS

ZZD had the highest content of naringin (6348.1 mg/L), and could significantly increase the 24 h defecations (1.10- to 1.42-fold), fecal moisture (1.14-fold) and intestinal transport rate (1.28-fold) of STC mice, increased the thickness of the mucosal and muscular tissue (1.18- to 2.16-fold) and regulated the neurotransmitters in the colon of STC mice. Moreover, ZZD significantly activated the AHR signaling pathway, and also affected the composition of gut microbiota in STC mice.

DISCUSSION AND CONCLUSIONS

The beneficial effect and the possible mechanism of ZZD on STC could provide a theoretical basis for the broader clinical application of ZZD.

Interaction of lipophilic VIP derivatives with recombinant VIP1/PACAP and VIP2/PACAP receptors

Stearyl vasoactive intestinal polypeptide has been reported to be a VIP (vasoactive intestinal polypeptide) receptor agonist of high potency with an original bioavailability and action. We synthesized three fatty acyl derivatives, myristyl-, palmityl- and stearyl-[Nle17]VIP, and tested their capacity to recognize recombinant rat- and human VIP1- and VIP2/PACAP (pituitary adenylate cyclase-activating polypeptide) receptors and to stimulate adenylate cyclase activity. The three lipophilic analogues bound with high affinity (from 0.5 to 20 nM) to both receptor subtypes but did not distinguish between them. In preparations expressing a high density of human VIP1/PACAP receptors, the three lipophilic analogues had the same efficacy as VIP and [Nle17]VIP. In preparations expressing the rat receptors, stearyl-[Nle17]VIP had a lower efficacy than the other peptides tested. In preparations expressing a low level of VIP1/PACAP receptors and in those expressing VIP2/PACAP receptors, all analogues behaved like partial agonists. The lowest efficacy was observed for stearyl-[Nle17]VIP on the VIP2/PACAP receptor subclass. Based on our results, a complex pattern of in vivo biological effects of the lipophilic VIP derivatives should be expected: these compounds might behave as full agonists, partial agonists, or antagonists of the VIP response, depending on the number and the subtype of receptor expressed.

Regulation of inducible and neuronal nitric oxide synthase gene expression by interferon-gamma and VIP

The studies examined the regulation of inducible and neuronal nitric oxide synthases (iNOS and nNOS, respectively) in the rat brain, stomach, rectum, and spleen. Relative expression of iNOS and nNOS mRNAs was quantified by the sensitive method of polymerase amplification reactions. The NOS proteins were determined by Western blot, using specific antibodies. Highest levels of nNOS and iNOS mRNAs were expressed in the rat brain and spleen, respectively. Furthermore, both nNOS and iNOS were expressed in the stomach and rectum. Interestingly, treatment of tissues with lipopolysaccharides or cytokine interferon-gamma (IFN-gamma) induced the expression of iNOS and decreased that of nNOS, representing a shift from one isoform to the other. When the tissues were treated with IFN-gamma followed by vasoactive intestinal polypeptide (VIP), the induction of iNOS was reduced by VIP. The changes in iNOS and nNOS expression at the transcriptional level corresponded to those at the translational level. The data suggest a regulatory role of IFN-gamma and VIP in the expression iNOS and nNOS and a counterregulation of iNOS and nNOS in rat tissues.

Vasoactive intestinal polypeptide gene expression is characteristically higher in opossum gastrointestinal sphincters

BACKGROUND/AIMS

Vasoactive intestinal polypeptide (VIP) has been suggested to be an inhibitory neurotransmitter in the sphincteric and nonsphincteric smooth muscles of the gut. However, the relative gene expression of VIP in these functionally diverse regions is not known.

METHODS

The gastrointestinal smooth muscle sphincters of opossums were excised from the adjoining nonsphincteric smooth muscles. RNAs were isolated and subjected to blot hybridizations with VIP complementary DNA probe. Relative expression of VIP gene was quantitated using the densitometric scanning of the VIP messenger RNA (mRNA) transcripts. The cellular specificity of VIP gene expression was investigated in cultures of neuroblastoma cells and myenteric plexuses and compared with those of the smooth muscle cells.

RESULTS

The data showed higher levels of VIP mRNA in the sphincteric than the adjoining nonsphincteric tissues. VIP mRNA were found in significantly higher amounts in the myenteric neurons and neuroblastoma cells than in the smooth muscle cells.

CONCLUSIONS

VIP gene expression was significantly higher in the sphincteric smooth muscle regions than in the nonsphincteric regions of the gut. The studies provide further evidence for the role of VIP in neurotransmission of the gut.

Molecular cloning and functional characterization of a human liver vasoactive intestinal peptide receptor

We have isolated a cDNA from a human liver library which is 2349 base pairs in length and encodes a near-full length seven transmembrane receptor (432 amino acids), 85% homologous to the amino acid sequence for the rat vasoactive intestinal peptide (VIP) receptor. Northern blot analysis identifies a major species at 3.3 kb in lung, and to a lesser extent in brain, heart and liver. In order to confirm the identity of this human clone, double-stranded oligonucleotides encoding the signal peptide of the rat VIP receptor were constructed by polymerase chain reaction and attached to the 5' end of the human clone. COS cells transiently transfected with this human VIP receptor chimera, express a single binding site for 125I-VIP with a Kd of 9.2 +/- 2 nM. Related peptides displace 125I-VIP with a relative potency of VIP = PACAP > helodermin >> PHM > secretin, which is similar to the binding profile seen in human tissues. This human chimeric receptor is functionally coupled to the stimulation of adenylyl cyclase in transfected COS cells, as evidenced by a dose-dependent increase in intracellular cAMP accumulation. These studies indicate that this cDNA encodes a human liver VIP receptor which is functionally coupled to the activation of adenylyl cyclase.

The effect of vasoactive intestinal polypeptide on the lower esophageal sphincter in achalasia

Vasoactive intestinal polypeptide (VIP) is one of the main neurotransmitters implicated in the relaxation of the lower esophageal sphincter (LES). The effect of exogenous VIP on LES motor activity was determined by esophageal manometry. LES pressure (LESP) and LES relaxation were compared in four healthy volunteers and in six patients with achalasia. The effects of intravenous doses of 1.5, 3, and 5 pmol.kg-1.min-1 of VIP were compared with placebo. Neither placebo nor 3 and 5 pmol.kg-1.min-1 of VIP produced any effect on esophageal motility in healthy volunteers. In achalasia the three doses of VIP caused a dose-dependent decrease in LESP with a significant improvement in LES relaxation. A dose of 5 pmol.kg-1.min-1 produced a maximal decrease of 51% in LESP. A beta-adrenergic agonist, isoproterenol, caused a decrease in LESP both in healthy volunteers and in patients with achalasia without improving LES relaxation. In summary, intravenous VIP improved LES relaxation and caused a decrease in LESP in patients with achalasia without affecting LESP in healthy volunteers, indicating that the LES muscle in achalasia is supersensitive to VIP. The current study suggests that a selective damage in the noncholinergic nonadrenergic innervation of the esophagus is in part responsible for the motor alteration seen in these patients. The findings and the inability of isoproterenol to improve LES relaxation despite decreasing LESP support a role in VIP as a indicator of LES relaxation.

Responses of porcine gastric and duodenal smooth muscle to VIP

1. Mechanical activity was recorded in isolated muscle preparations from circular and longitudinal layers of gastric fundus, corpus and antrum and from the duodenum of pigs, using conventional organ bath technique. Rectangular current pulses were applied to the muscle strips for electrical field stimulation (EFS). 2. Fundic and circular corpus preparations developed a marked spontaneous tonic activity. Vasoactive intestinal polypeptide (VIP, 10(-9)-10(-7) mol l-1) inhibited this spontaneous activity. This inhibitory effect was not affected by application of tetrodotoxin (TTX) showing its myogenic nature. 3. Pretreatment of fundic and circular corpus preparations with VIP reduced the excitatory responses to substance P, bombesin, serotonin and histamine, but it had no effect on the acetylcholine (ACh)-induced tonic and phasic activity. 4. Longitudinal duodenal preparations showed purely phasic activity which was almost insensitive to VIP. In circular duodenal preparations particularly strong spontaneous tonic contractions were observed which could be inhibited by VIP. 5. Circular duodenal preparations excised 3-5 cm postpyloric had a spontaneous tone which could reach up to 80% of the maximum contractions induced by 10(-4) mol l-1 ACh. These preparations were chosen for further pharmacological studies and for experiments with EFS. VIP was the most powerful substance for the inhibition of spontaneous tone, followed by serotonin, PGE2 and bradykinin. This type of preparation exhibited particularly strong inhibitory effects to EFS; even single stimuli could induce near maximum relaxation. The inhibition induced by EFS was unaffected by treatment with ATP, guanethidine, atropine, methysergide and apamin. TTX completely abolished the EFS-induced relaxation, showing its neurogenic nature. 6. Porcine circular duodenum is a good model for studying the transmitter system of the non-adrenergic, non-cholinergic (NANC) innervation. The results are consistent with the assumption that VIP is the transmitter in this system, although the very slow time-course of the VIP-induced inhibition in comparison with the EFS-induced inhibition is not consistent with this notion.

Gallbladder function and gastric liquid emptying in achalasia

Because of evidence that the abnormalities in achalasia are not restricted to the distal esophagus, we investigated gallbladder function by cholescintigraphy in the steady state and in response to CCK and the scintigraphic gastric emptying of a liquid caloric meal in 10 individuals with achalasia and 10 normal controls. No abnormalities were found during the filling phase of the gallbladder but seven of the 10 patients showed a 50% reduction in the ejection fraction (39.4% +/- 30.4 vs 80.3 +/- 8.3 of controls, mean +/- SD, P = 0.007) and a slower than normal ejection phase (9.1%/min +/- 6.6 vs 18.1 +/- 4.5, P = 0.02. In eight of the 10 patients, gastric liquid emptying was accelerated with a T1/2 of 41.5 min +/- 15.4 vs 74.7 min +/- 11.5 in the controls (P = 0.007). It is concluded that in some achalasia patients extraesophageal functional abnormalities of the gastrointestinal tract may be found. Whether these findings are promoted by degenerative charges of extraesophageal nerve fibers as well as their clinical significance require further investigations.

Transcutaneous electrical nerve stimulation decreases lower esophageal sphincter pressure in patients with achalasia

Vasoactive intestinal peptide (VIP) is believed to be an inhibitory neurotransmitter responsible for lower esophageal sphincter (LES) relaxation. In patients with achalasia the concentration of VIP and the number of VIP-containing nerve fibers are reduced or absent. It has been suggested that the response to low-frequency transcutaneous electrical nerve stimulation (TENS) may be mediated by a nonadrenergic noncholinergic pathway in which the release of VIP is responsible for the smooth muscle relaxation. The present study was designed to evaluate the effect of TENS on LES pressure and on VIP plasma concentrations in six patients with achalasia (five female, one male). TENS was performed daily during one week for 45-min sessions with a pocket stimulator that delivered low-frequency pulses (6.5 Hz), at 10 pulses/sec of 0.1-msec duration at intensities of 10-20 mA until rhythmic flexion of the fingers was obtained without producing pain. LES pressure and VIP levels were obtained before TENS, after the first 45-min session, and after a week of daily stimulation. After 45-min, TENS produced a significant reduction (P less than 0.01) in LES resting pressure from the mean value 56 +/- 6.4 mm Hg to 42.3 +/- 6.4 mm Hg; with LES relaxation improvement from 50.6 +/- 3% to 63.1 +/- 3.2% (P less than 0.01). After one week of daily TENS, an additional reduction in LES resting pressure (40.3 +/- 4 mm Hg) was observed (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

High vasoactive intestinal polypeptide plasma levels in patients with Barrett's esophagus

We have evaluated the correlation between vasoactive intestinal polypeptide (VIP) plasma concentration and severity of gastroesophageal reflux in patients with Barrett's esophagus and the possible differences in the VIP values of these patients compared with healthy volunteers. We also evaluated the relation between VIP plasma concentration and lower esophageal sphincter (LES) pressure in 24 patients with Barrett's esophagus. The mean VIP plasma concentration in 14 patients with severe gastroesophageal reflux was 25.6 +/- 0.75 pg/ml, significantly higher than the mean value observed in 10 patients with moderate reflux (18.9 +/- 0.67 pg/ml) (p less than 0.01). The mean LES resting pressure was significantly lower in the group of patients with severe gastroesophageal reflux than that observed in patients with moderate reflux (3 +/- 0.64 and 10.3 +/- 0.69 mm Hg, respectively; p less than 0.01). The mean VIP plasma concentration in 11 healthy volunteers (20.6 +/- 0.65 pg/ml) was significantly lower than the mean value observed in the subgroup of patients with severe gastroesophageal reflux (p less than 0.01). VIP values in patients with moderate reflux were not significantly different from those observed in our volunteers. There was a significant correlation between LES pressure and VIP plasma level (r = -0.9253; p less than 0.01). In conclusion, it is possible that the decreased LES resting pressure observed in patients with Barrett's esophagus and severe gastroesophageal reflux may be due to impairment of the VIPergic innervation, resulting in an increased local VIP release with possible overflow to peripheral plasma.

Slow transit chronic constipation (Arbuthnot Lane's disease). An immunohistochemical study of neuropeptide-containing nerves in resected specimens from the large bowel

Seven patients (6 women, 1 man) with severe idiopathic chronic constipation, who underwent surgery with subtotal colectomy and ileorectal anastomosis, were investigated for the occurrence and density of nerve fibres, immunoreactive to different neuropeptides in the mucosa, submucosa, ganglia and smooth muscle in fresh specimens from the colon ascendens, the colon transversum and the colon descendens-sigmoideum. The following substances were studied: enkephalin, substance P, somatostatin, neuropeptide Y, vasoactive intestinal polypeptide, calcitonin gene-related peptide, bombesin, motilin, tyrosine hydroxylase, dynorphin and galanin. Nerve fibres immunoreactive to CGRP occurred in large numbers in the myenteric ganglia of the patients with severe idiopathic chronic constipation, whereas in the myenteric ganglia of the control cases they only occurred in low numbers. In two patients there was no detectable motilin immunoreactivity and in one patient only sparse in the mucosa and the smooth muscle. The other neuropeptides investigated occurred in the density and distribution previously reported in the normal gut. With the present technique there were indications that patients with severe idiopathic chronic constipation have a significant difference in the occurrence of immunoreactive nerve fibres to CGRP and motilin compared to control patients.