Distribution of nitric oxide synthase in stomach myenteric plexus of rats

Differential expression of multidrug resistance protein 5 and phosphodiesterase 5 and regulation of cGMP levels in phasic and tonic smooth muscle

Previous studies have identified differences in the expression of proteins that regulate myosin light chain phosphorylation and contraction in tonic and phasic smooth muscle. cGMP plays a critical role in smooth muscle relaxation and is important for optimal function of phasic and tonic smooth muscle. The intracellular cGMP levels are regulated by its hydrolysis via phosphodiesterase 5 (PDE5) and efflux via novel multidrug resistance protein 5 (MRP5). In the present study we tested the hypothesis that the differences in the phasic and tonic behavior of smooth muscles may be related to differences in mechanisms that terminate cGMP signaling. Expression of PDE5 and MRP5 was significantly (more than 2-fold) higher in fundus compared with antrum. The NO donor S-nitrosoglutathione (GSNO) caused an increase in PDE5 activity and intra- and extracellular cGMP levels in both fundus and antrum. Stimulation of PDE5 activity and increase in extracellular cGMP were significantly higher in fundus, whereas increase in intracellular cGMP was significantly higher in antrum. GSNO-induced increase in extracellular cGMP was blocked in dispersed cells by the cyclic nucleotide export blocker probenecid and in cultured muscle cells by depletion of ATP or suppression of MRP5 by siRNA, providing evidence that cGMP efflux was mediated by ATP-dependent export via MRP5. Consistent with the higher expression and activity levels of PDE5 and MRP5, GSNO-induced PKG activity and muscle relaxation were significantly lower in muscle cells from fundus compared with antrum. Thus higher expression of PDE5 and MRP5 in muscle cells from fundus correlates with tonic phenotype of muscle.

TRPV2 ion channels expressed in inhibitory motor neurons of gastric myenteric plexus contribute to gastric adaptive relaxation and gastric emptying in mice

Gastric adaptive relaxation (GAR) is impaired in ~40% of functional dyspepsia (FD) patients, and nitric oxide (NO) released from inhibitory motor neurons plays an important role in this relaxation. Although the underlying molecular mechanism of GAR is poorly understood, transient receptor potential channel vanilloid 2 (TRPV2) mechano- and chemoreceptors are expressed in mouse intestinal inhibitory motor neurons and are involved in intestinal relaxation. The aim of this study was to evaluate the distribution of TRPV2 in inhibitory motor neurons throughout the mouse gastrointestinal tract and the contribution of TRPV2 to GAR. RT-PCR and immunohistochemical analyses were used to detect TRPV2 mRNA and protein, respectively. Intragastric pressure was determined with an isolated mouse stomach. Gastric emptying (GE) in vivo was determined using a test meal. TRPV2 mRNA was detected throughout the mouse gastrointestinal tract, and TRPV2 immunoreactivity was detected in 84.3% of neuronal nitric oxide synthase-expressing myenteric neurons in the stomach. GAR, which was expressed as the rate of decline of intragastric pressure in response to volume stimuli, was significantly enhanced by the TRPV2 activator probenecid, and the enhancement was inhibited by the TRPV2 inhibitor tranilast. GE was significantly accelerated by TRPV2 agonist applications, and the probenecid-induced enhancement was significantly inhibited by tranilast coapplication. Mechanosensitive TRPV2 was expressed in inhibitory motor neurons in the mouse stomach and contributed to GAR and GE. TRPV2 may be a promising target for FD patients with impaired GAR.

Nitric oxide synthase inhibition results in immediate postoperative recovery of gastric, small intestinal and colonic motility in awake rats

BACKGROUND

Nitric oxide (NO) is known to inhibit gastrointestinal motility. However, no detailed analysis of gastric, small intestinal and colonic motor effects, including effects on contraction frequency, has, as yet, been reported after NO inhibition in awake rats. We therefore investigated the effects of NO synthase inhibition on gastric, small intestinal and colonic motility in awake rats under baseline conditions and in a postoperative ileus model.

METHODS

In Sprague-Dawley rats, strain gauge transducers were sutured either to the gastric corpus, the small intestine or the colon. After 3 days, L-NMMA (NO synthase inhibitor), D-NMMA or vehicle was given i.v., while the motility was recorded continuously. In addition, postoperative gastric, small intestinal or colonic motility was investigated after L-NMMA or vehicle treatment prior to abdominal surgery. The motility index, the contraction amplitude, the area under the contraction amplitude and the contraction frequency were analysed.

RESULTS

L-NMMA decreased gastric motility to 60+/-8% for about 15 min, but continuously increased small intestinal motility to 221+/-22% and colonic motility to 125+/-7% compared to baseline (baseline=100%; p<0.01 for all comparisons). L-NMMA increased the contraction frequency throughout the gastrointestinal tract (stomach, 13+/-2%; small intestine, 8+/-1%; colon, 16+/-5%; p<0.01 vs. baseline for all comparisons). L-NMMA injection prior to surgery did not prohibit intraoperative inhibition of gastrointestinal motility, but did result in immediate recovery of gastric, small intestinal and colonic motility postoperatively (L-NMMA vs. vehicle, 0-60 min postoperatively; stomach, 90+/-9% vs. 53+/-3%; small intestine, 101+/-5% vs. 57+/-3%; colon, 134+/-6% vs. 60+/-5%; p<0.01 for all comparisons; no significant difference between preoperative baseline motility and L-NMMA treated rats postoperatively).

CONCLUSIONS

Under baseline conditions, endogenous NO inhibits small intestinal and colonic motility and gastric, small intestinal and colonic contraction frequency in awake rats. In the early postoperative period, endogenous NO is a major inhibitory component that seems to constitute the common final pathway of mediators and the neural pathways inhibiting gastrointestinal motility in rats.

Role of inhibitory neurotransmitter of myoenteric plexus in carcinogenesis of irritable bowel syndrome with different subtypes

AIM: To investigate the role of inhibitory neurotransmitter of myoenteric plexus in the carcinogenesis of constipation and diarrhea-predominant irritable bowel syndrome (C-IBS and D-IBS) in rats.

METHODS: Rat model of D-IBS was established by intracolonic instillation of acetic acid and restraint stress, while the positive and blank control were designed; Rat model of C-IBS was established by stomach irrigation with 0-4°C cool water daily for 14 d, while the positive and blank control were also designed. The bowel movement, the properties of fecal pellets, visceral sensitivity, and the content of nitric oxide (NO) in the myoenteric plexus were detected in the rats of each group.

RESULTS: The contraction frequency of the abdominal muscle in D-IBS group was significantly enhanced as compared with that in C-IBS, positive and blank control group (1.2 mL volume: 7.22±2.01 vs 2.77±0.78, 2.89±1.17, 3.59±1.08; 1.6 mL volume: 8.11±1.94 vs 2.89±1.67, 2.44±1.42, 2.89±1.22, P < 0.05) at high intensities of colorectal distention (CRD); while at low intensities of CRD, the contraction frequency in C-IBS group was significantly reduced as compared with that in D-IBS group (0.4 mL volume: 0.44±0.22 vs 2.44±0.67; 0.8 mL volume: 1.56±0.74 vs 6.31±1.74, P < 0.05). The amount, wet weight, and water ratio of the feces expelled by the rats in C-IBS and positive control group were significantly lower than those in blank control group (2.00±0.66, 2.33±0.50 vs 3.67±1.00; 0.80±0.32, 1.69±0.49 vs 2.14±0.27; 39.24±3.11, 40.67±2.84 vs48.38±2.79, P < 0.05); while the weight and water ratio of the feces in D-IBS group were markedly higher than those in positive and blank control group (2.31±0.72 vs 1.52±0.58, 1.57±0.56, P < 0.05; 65.31±3.31 vs 53.41±2.73, 55.78±3.99, P < 0.05). The time before the first melena defecation in C-IBS group was significantly longer than that in positive and blank controls (277.89±25.08 vs 205.44±15.74, 189.22±18.45, P < 0.05). There were no signs of colonic inflammation in the rats of each group. The number of NO positive neurons in rats of the C-IBS group was notably larger than that in D-IBS and blank control group (303.50±14.43 vs 200.89±16.67, 185.78±16.66, P < 0.01), but no obvious difference existed between D-IBS and blank control group (P >0.05).

CONCLUSION: The enhanced inhibitory neurotransmitter NO in the myoenteric plexus of colon is related to the IBS subgroups, visceral sensitivity, and motility dysfunction. The result reveals that the change of NO is related to the occurrence of different IBS subgroups.

Effect of noradrenaline on nitric oxide action in the contraction of mouse duodenal muscle strips

AIM: To investigate the effect of nitric oxide (NO) on the contraction of isolated mouse duodenal muscle strip (DMS), and the influence of noradrenaline (NA) on the action of NO.

METHODS: DMS isolated from mice were suspended in tissue chambers containing Krebs solution (10 mL, 37±1 ℃), with a continuing supply of gas mixture (950 mL/LCO₂, 50 mL/LO₂) from the bottom. L-Arg was used to produce NO. Contraction of DMS in the presence of NO and NA was recorded with tension transducer. ODQ (inhibitor of sGC), L-NNA (general inhibitor of NOS), and phentolamine (blocker of a adrenergic receptor) were used to explore the relationship between NO and NA.

RESULTS: L-Arg at concentrations from 2×10^-5 to 2×10^-2 mol/L decreased the DMS contractile amplitude in a dose-dependent manner (P<0.001). No significant effect was observed when L-Arg was used at the concentration of 2×10^-6 mol/L. Similarly, NA dose-dependently decreased the DMS contractile amplitude at concentrations ranging from 1.2×10^-7 to 1.2×10^-4 mol/L (P<0.001), but no significant effect was noted at 2×10^-8 mol/L. At 1.2×10^-8 mol/L, NA increased the effect of L-Arg at concentrations from 2×10^-6 to 2×10^-3 mol/L on the contraction of DMS (P<0.001); Furthermore, at 1.2×10^-6 mol/L, NA enhanced the effect L-Arg at all concentrations from 2×10^-6 to 2×10^-2 mol/L (P<0.001). This effect of L-Arg was inhibited by L-NNA, ODQ and phentolamine (P<0.001).

CONCLUSION: NO can inhibit the contraction of the DMS, which can be synergized by NA through augmenting NO synthase activity or via a post-receptor mechanism.

Effects of neurotrophins on gastrointestinal myoelectric activities of rats

AIM: To observe the effects of mouse nerve growth factor (NGF), rat recombinant brain derived neurotrophic factor (rm-BDNF) and recombinant human neurotrophin-3 (rh-NT-3) on the gastrointestinal motility and the migrating myoelectric complex (MMC) in rat.

METHODS: A randomized, double-blinded, placebo-controlled experiment was performed. 5-7 days after we chronically implanted four or five bipolar silver electrodes on the stomach, duodenum, jejunum and colon, 21 experimental rats were coded and divided into 3 groups and injected NGF, rm-BDNF, rh-NT-3 or placebo respectively via tail vein at a dose of 20 μg·kg^{- 1}. The gastrointestinal myoelectrical activity was recorded 2 hours before and after the test substance infusions in these consciously fasting rats.

RESULTS: The neurotrophins-induced pattern of activity was characterized by enhanced spiking activity of different amplitudes at all recording sites, especially in the colon. In the gastric antrum and intestine, only rh-NT-3 had increased effects on the demographic characteristics of electrical activities (P < 0.05), but did not affect the intervals of MMCs. In the colon, all the three kinds of neurotrophins could significantly increase the frequency, amplitude and duration levels of spike bursts, and also rh-NT-3 could prolong the intervals of MMC in the transverse colon (25 ± 11 min vs 19 ± 6 min, P < 0.05). In the distal colon rh-NT-3 could evoke phase III-like activity and disrupt the MMC pattern, which was replaced by a continuously long spike bursts (LSB) and irregular spike activity (ISA) for 48 ± 6 min.

CONCLUSION: Exogenous neurotrophic factors can stimulate gut myoelectric activities in rats.

Gastrointestinal smooth muscle cell as target for gene transfer of eNOS gene

AIM

To generate an adenoviral vector carrying endothelial nitric-oxide synthase (eNOS) gene in order to mediate the expression of eNOS gene in gastrointestinal smooth muscle cells (SMC) and assess the enzyme activity of eNOS.

METHODS

A recombinant adenovirus (Ad-eNOS) containing the bovine eNOS cDNA fragment was generated by homologous recombination in bacteria. The SMC of distal part of esophagus and gastric fundus of cat were isolated and cultured in vitro and infected with Ad-eNOS. The expression of eNOS gene was detected by Western blot and RT-PCR. The enzyme activity of NOS and the output of NO in SMC were measured by NOS and NO assay kit, furthermore, the different effects of given factors on the enzyme activity and the yield of NO were studied.

RESULTS

The Ad-eNOS can infect the cultured SMC efficiently (MOI = 50, infection rate = 74%). Western blot and RT-PCR confirmed the expression of eNOS in those infected cells. After the cells had been infected with Ad-eNOS, the basal activity of NOS significantly increased from 47±13 nkat/L to 93±13/L (P<0.05), and the level of NO in cell culture supernatants increased by 3 fold (45±13 vs 16±7 μmol/L). In the presence of L-arginine (NOS enzyme substrate), calcium, EGTA (calcium chelating agent), and L-NAME (NOS inhibitor), NOS activity was 94±8, 173±25, 29±6, 58±11 nkat/L and NO level was 48±14, 106±18, 6±2, 17±11 μmol/L, respectively.

CONCLUSION

The constructed recombinant adenovirus, Ad-eNOS, can efficiently mediate the expression of eNOS gene in cultured SMC of digestive tract. The activity of eNOS can be regulated by the concentration of calcium. L-arginine is Not the rate-limiting step for nitric oxide generation from endothelial nitric oxide synthase.

Significance of changes of gastrointestinal peptides in blood and ileum of experimental spleen deficiency rats

AIM: To explore the mechanism of spleen deficiency (SD) by studying the relationship of gastro-intestinal peptides level and ileal electro-mechanical activity of SD rats and cold restrain rats.

METHODS: (1) spleen deficiency (SD) model was established by feeding Houpou:Zhishi: Dahuang in the ratio of 3:3:2, 3 ml/time, for 42 days. (2) The cold restrain stress model: Animals were restrained on grille and placed in a cool water at 18 °C for 3 h. (3) Substance P (SP) and vasoactive intestinal peptide (VIP) levels in all layers of initial part of ileum and blood in rats were measured by radioimmunoassays (RIA) while changes of electric activity and motility in ileum of rats were recorded with electrode and strain gauge.

RESULTS: SP levels in ileum and blood of experimental SD rats were significantly higher than that of the control groups (9.89 ± 5.65 vs 1.22 ± 1.18, P < 0.005, in ileum; 22.7 ± 3.95 vs 6.60 ± 1.47, P < 0.001, in blood) while the VIP levels of the SD rats were significantly lower than that of the controls (3.50 ± 2.01 vs 9.10 ± 4.91, P < 0.05, in ileum; 229.8 ± 62.4 vs 560.4 ± 151.3, P < 0.001, in blood). As compared with the controls, the average frequency of slow electric waves (21.3 ± 0.96 vs 18.2 ± 2.28, P < 0.05) and motility (21.5 ± 0.58 vs 18 ± 2.65, P < 0.005) of SD rats increased obviously and the frequency of fast waves of SD rat also increased. In spontaneous recovery cases, SP levels recovered significantly (compared with the SD groups, 2.99 ± 0.62 vs 9.89 ± 5.65, P < 0.001, in ileum; 14.4 ± 4.22 vs 22.7 ± 3.95, P < 0.001, in blood) but did not drop to normal. After the SD rats treated with Chinese herbs (Jiawei Sijun zi Tang), SP improved (compared with SD cases, 2.20 ± 1.25 vs 9.89 ± 5.65, (P < 0.001), in ileum; 10.7 ± 1.88 vs 22.7 ± 3.95, (P < 0.001), in blood) and VIP in blood also improved (compared with SD rats, 485.7 ± 229.0 vs 229.8 ± 62.4, P < 0.01) while the amplitude of motility decreased apparently (compared with the SD rats, 0.64 ± 0.096 vs 0.89 ± 0.15, P < 0.01). The ileal SP levels of cool stress didn’t change while the ileal VIP levels of cool stress became significantly lower than that of the control groups (2.87 ± 0.87 vs 9.10 ± 4.91, P < 0.01). The blood SP levels of cool stress were significantly higher (15.60 ± 1.83 vs 6.60 ± 1.47, P < 0.001) whereas the blood VIP levels of cool stress were significantly lower than that of the control group (153.4 ± 70.46 vs 560.4 ± 151.30, P < 0.001).

CONCLUSION: Changes of SP and VIP levels in initial part of ileum and blood of SD rats and cool stress rats may be closely related to the gastrointestinal motility disorders presented in SD and cool stress rats. the Chinese herbs (Jiawei Sijun zi Tang) currently used have partially therapeutic effect.

Effect of oxytocin on contraction of rabbit proximal colon in vitro

AIM: To investigate the effects of oxytocin (OT) on isolated rabbit proximal colon and its mechanism.

METHODS: Both longitudinal muscle (LM) and circular muscle (CM) were suspended in a tissue chamber containing 5 mL Krebs solution (37 °C), bubbled continuously with 950 mL·L^-1 O2 and 50 mL·L^-1 CO2. Isometric spontaneous contractile responses to oxytocin or other drugs were recorded in circular and longitudinal muscle strips.

RESULTS: OT (0.1 U·L^-1) failed to elicit significant effects on the contractile activity of proximal colonic smooth muscle strips (P > 0.05). OT (1 to 10 U·L^-1) decreased the mean contractile amplitude and the contractile frequency of CM and LM. Hexamethonium (10 μmol·L^-1) partly blocked the inhibition of oxytocin (1 U·L^-1) on the contractile frenquency of CM. N^ω-nitro-L-arginine-methylester (L-NAME, 1 μmol·L^-1), progesterone (32 μmol·L^-1) and estrogen (2.6 μmol·L^-1) had no effects on OT-induced responses.

CONCLUSION: OT inhibits the motility of proximal colon in rabbits. The action is partly relevant with N receptor, but irrelevant with that of NO, progesterone or estrogen.

Effects of Chinese herb complex Jianpiwan and Baohewan on gastrointestinal motility in rats

AIM: To investigate the effects of Jianpiwan and Baohewan on gastrointestinal motility in rats.

METHODS: Using dextran blue 2000 as a gastrointestinal internal marker its relative remaining rate in stomach and its pushing ratio of the bowel, we observed the effects of Jianpiwan and Baohewan on the emptying of stomach and the driving of bowel in normal and splenic asthenic rats.

RESULTS: Baohewan and Jianpiwan had evidently promoting effect on emptying of stomach in normal and splenic asthenic rats 0.029±0.033 vs 0.059±0.035; 0.018±0.010 vs 0.059±0.035; 0.036±0.028 vs 0.089±0.042; 0.029±0.026 vs 0.089±0.042 (P < 0.05). Baohewan had better effect than Jianpiwan on the driving of bowel in normal rats 58.8±11.3 vs 51.6±9.7 (P < 0.05). For splenic asthenic rats whose vermiculation was reinforced, Baohewan still had promoting effect 63.5±6.1 vs 54.1±12.3 (P < 0.05) and Jianpiwan can slow the vermiculation and help it recover to normal leves 43.0±7.1 vs 54.1±12.3 (P < 0.05).

CONCLUSION: Baohewan and Jianpiwan have promoting and adjusting effects on gastrointestinal motility in rats.

Gastrin, somatostatin, G and D cells of gastric ulcer in rats

AIM: To investigate the relationship among gastrin, somatostatin, G and D cells in gastric ulcer and in its healing process in rats.

METHODS: Fourty-nine Wistar rats were divided into 7 groups. The gastric ulcer model was induced by acetic acid successfully. The gastrin and the somatostatin in rat plasma, gastric fluid and antral tissue were measured by radioimmunoassay (RIA). G and D cells in antral mucosa were analyzed with polyclonal antibody of gastrin and somatostatin by immunohistochemical method and Quantimet 500 image analysis system.

RESULTS: In gastric ulcer, the level of gastrin in plasma, gastric fluid, and antral tissue increased, that of somatostatin declined, and the disorder gradually recovered to the normal level in the healing process. Immunohistochemical technique of G and D cells in antral mucosa demonstrated that the number of G cells increased and that of D cells decreased, both areas of G and D cells declined, the ratio of number and area of G/D increased in gastric ulcer, and the disorder gradually recovered in the healing process.

CONCLUSION: In gastric ulcer, the increased gastrin secreted by G cells, the declined somatostatin secreted by D cells, and the disordered G/D cell ratio can lead to gastrointestinal dysfunction.