| Background &Aims:Gaseous transmitters, such as nitric oxide (NO) and carbon monoxide (CO), are a family of regulatory molecules that involved in regulation of physiological functions of mammalian, including human beings. Hydrogen sulphide (H2S) is a chemical hazard of gas production. It is colorless and smells like rotten eggs. Relatively high endogenous levels of H2S have recently been detected in the blood, brain, kidney and liver, indicating that H2S plays physiological role in regulationg the functions fo these organs. H2S may be the third gaseous transmitter in addition to NO and CO.Endogenous H2S can be synthesized from L-Cysteine through the cystathionineγ-lyase(CSE) and cystathionineβ-synthase (CBS).Sodium hydrogen sulfide (NaHS, a donor of exogenous H2S) has been widely used in the experiment related to H2S because it dissociates into Na+ and HS- in solution, and HS- then associates with H+ and produces H2S. It is reported that H2S function as a smooth muscle relaxant in gastrointestinal tract, but the mechanism is uncertain. Rudolf Schicho et al found that CSE was expressed in the enteric neurons in the Guinea Pig and Human Colon. So H2S might mediate gastrointestinal tract via enteric nervous system. The aim is to study the effect and mechanism of H2S on gastric motility.Methods:Surgical procedures and recording of intragastric pressure in vivo.The rats were anesthetized by pentobarbital sodium of 2% (56mg/kg i.p.). The trachea of rat was cannulated to facilitate the ventilation, a catheter was inserted into the left jugular vein to infuse fluid and the left femoral artery was cannulated. A plastic ballonet made of the condom was inserted into the stomach to monitor intragastric pressure (IGP). Normal saline was infused into the ballonet to maintain the pressure in the ballonet at about 25 mmHg. The stomach was initially adapted for at least 1h before performing experiments to stabilize the background motility after surgery.Gastric smooth muscle strips preparation and smooth muscle tension recording in vitro.Rats were sacrificed by cervical dislocation. The stomach was removed immediately and placed in a Petri dish containing oxygenated Krebs solution (4℃). The preparations of longitudinal muscle strips about 4 mm wide and 10 mm long were rapidly dissected parallel to the trend of mucosa of gastric body and were suspended in tissue chambers containing 5 ml warmed (37℃) and continuously oxygenated (95% O2:5% CO2) Krebs solution. In order to stabilize the spontaneous contraction, the muscle strips we equilibrated for at least lh with flushing every 15 min.Statistical AnalysisIn the in vivo studies, intragastric pressures were measured. Mean pressure for 3-min period before administration was taken as the baseline. The mean pressure after treatment was taken as the effective value. In the experiments on muscle strips, the average tension for 3-min period before administration was taken as the baseline. The average tension after treatment was taken as the effective value. The effective value was normalized to a standardized ratio R.The value are presented as mean±SEM. Differences between groups were evaluated by One way ANOVA and Students't test, P < 0.05 was considered to be significantly different.Result:1. After systemic administration of NaHS (5.6mg/kg, i.p.) or L-Cysteine (12mg/kg, i.p.), IGP decreased significantly and gradually returned to normal. 2.NaHS (5×10-4 - 10-3M) significantly inhibited the contraction of muscle strips of gastric body but lower concentration of NaHS (10-4M) did not exert any effect. The contraction of muscle strips decreased immediately following NaHS administration, reached nadir at 10 min and returned to normal 30 min later.3.Pretreatment with glibenclamide(Gli, the inhibitor of KATP channel) (10-7M) significantly reversed the inhibitory effect of NaHS (10-3M) on the contraction of muscle strips, but pretreatment of tetrodotoxin (TTX, an antagonist of voltage-gated sodium channel) (10-6M) and N-nitro-L-argmine methyl ester (L-NAME) (10-4M) did not influenced it.4.L-Cysteine(1×10-3M - 5×10-3M ) significantly inhibited the spontaneous contraction of the longitudinal muscle strips of gastric body, but lower concentration of L-Cysteine (5×10-4M) did not influenced it. The tension of muscle strips dropped immediately following L-Cysteine administration, reached the nadir at 1-2 min and returned to normal in 10 min.5. Pretreatment with TTX (10-6 M) and atropine (the inhibitor of M receptor) (10-6 M), the inhibitory effect of L-Cysteine (10-3M) was significantly attenuated but was not affected by the pretreatment of L-NAME (10-4M) and glibenclamide (10-7M).6. PAG (10-6M-10-3M), the specific inhibitor of CSE, significantly increased the spontaneous contraction of muscle strips. The excitatory effect of PAG on muscle strips contraction lasted more than 30 min. AOAA (10-6M-10-5M), the specific inhibitor of CBS, exerted a similar effect as PAG7. Pretreatment of AOAA (10-6M) or PAG (10-6M) did not influenced the inhibitory effect of NaHS (10-3M) on the contraction of muscle strips, but significantly reversed that of L-Cysteine (10-3M).Conclusion:1. Both exogenous and endogenous H2S inhibited gastric motility in vivo and in vitro.2. The inhibitory effect of exogenous H2S on gastric motility is mainly through opening the KATP channels on the membrane of smooth muscle, but that of endogenous H2S is via the ENS and cholinergic nerve.3. Endogenous H2S exerted a tonic inhibition on gastric motility.
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