| Nitric oxide (NO) which generally accepted as a non-adrenergic non-cholinergic (NANC) neurotransmitter involved in NANC smooth muscle relaxation or contraction in tract plays a main role in gastrointestine,Histamine(His) is also an important mediator in tract. To evaluate the correlation between NO and His in guinea pig intestine,five parts of experiment were undertaken in this research. Sodium Nitroprusside (SNP) was used as exogeneous NO and 37 Tyrode solution oxygenated with a mixture of 95% O2 and 5% CO2 was used to mimic the physiological condition of small intestine.1. Effect of SNP on the contractile responses of isolated guinea pig ileumGuinea pig ileum segments were suspended vertically in organ baths contained oxygenated Tyrode solution maintained at 37,SNP(15 ymol/L,150 umol/L,1500u mol/L) was administered respetively,then recorded ileum contraction. The results showed that:SNP initially relaxed then contracted ileum with a higher frequency and intensity but a lower base-line tone.2. Influence of SNP on His HI effect of isolated guinea pig ileumThe condition was as same as 1. and His (0. 01 y mol/L -10 y mol/L) was aderministered in sequence into systems without or with SNP(15 u mol/L,150 y mol/L,1500 u mol/L,contacted 30 min). The results showed that:(1) SNP significantly strengthened H,effect induced by lower concentration of His (0.01 - 0.25 u mol/L,P<0. 05). (2) Above 0. 25 y mol/L,with the concentration of His increasing,the influence of SNP on H[ effect became more and more weaker. When His was increased to 1 and 10 u mol/L,only 1500 y mol/L SNP had a significant influence on H,effect (P<0. 05) .3. Influence of Nif on His H1 effect of isolated guinea pig ileum mediated by SNPThe condition was the same as 1. and nifedipine (Nif,25 n mol/L,50 n mol/L,100 n mol/L) was administered respectively to systems in the absence or presence of SNP(15 y mol/L,150 y mol/L,1500 y mol/L,contacted 30 min),then added His(0. 01 u mol/L - 10 y mol/L) in sequence to each system. The results showed that:(1) In systems contained with Nif,SNP could not strengthen ileum contraction as it did in systems without Nif and ileum segements became relaxed. (2)Nif concentration-dependently attenuated His H,effect mediated by SNP(P<0.001). (3) The inhibition by Nif was significantly different between groups with or without SNP at the concentration of 25 n mol/L and 50 n mol/L (P<0.05),but the inhibition became the same in all systems at the concentration of 100 n mol/L (P>0.05).4. Influence of SNP on His Ht effect in calcium-free Tyrode solutionSegments were mounted in organ baths contained calcium-free Tyrode solution,His (0.01 u mol/L - 10u mol/L) was administered in sequence in systems without or with SNP(15u mol/L,150 u mol/L,1500 y. mol/L,contacted 30 min) . The results showed that:(1) SNP relaxed ileum contraction in calcium-free Tyrode solution. (2) There was not any statistical difference in His H,effects among systems with or without SNP (P>0.05),it seems SNP was not involved in mediating His HI effect in calcium-free Tyrode solution,5. Kinetics of NO generation from SNP by thiolsUnder 37 and protected from light,release of NO from SNP in Tyrode solution by thiols of L-cysteine(CYS),glutathione(GSH),N-acetylcysteine(NAC),D-penicillamine, mercapto theanol,dimercaprol(BAL),dithiothreitol (DTT) in 25 mmol/L was measured by Griess assay with spectrophotometer (n=3). The results showed that:(1) Among the seven thiols,NO generation by CYS was significantly more than by other thiols (P<0.05) . (2) NO releasing from SNP by CYSwas in a first-order rate manner. Since CYS is widely exists in body and it was reported that its concentration varying showed little influence on NO formation,we inferred that in our system the concentration of SNP is equal to the concentration of NO.In conclusion:1. The generation of NO from SNP was related to maintaining the tensity and automatic contraction of isolated guinea pig ileum.2. SNP could strengthen His H,effect. The involve...
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