The role of nitric oxide in the relaxation effect of adenosine diphosphate in mouse gastric fundus

Different agents have been proposed as mediators of non-adrenergic non-cholinergic (NANC) system in gastric fundus. This study aimed to examine the role of adenosine diphosphate (ADP) and nitric oxide (NO) in the relaxation induced by activation of NANC in mouse stomach fundus. The isolated rings of fundus were prepared from gastric fundus of mice pretreated with reserpine (5mg/kg) and then mounted in the organ bath system. The isolatd tissues were suspended into 37˚C krebs’ solution containing atropine and bubbled by 95% 02 + 5% co(2-) the mechanical responses of gastric fundal strips were transmitted to a physiography via force-displacement transducer to record the tissue activities. The tissues contracted by 2x10-7M 5-hydroxytryptamine (5-HTP) were exposed to the electrical field stimulation (EFS) or 3x10-4 ADP to evaluate the role of NANC in mice fundal relaxation. NG-nitro-L-arginine methyl ester. (L-NAME), as inhibitor of nitric oxide synthase (NOS), and L-arginine (L-arg), as a precursor of NO formation, were used to test whether nitric oxide (NO) is involved as a mediator of inhibitory function of NANC system in the tested tissues. The results showed that in the presence of atropine (10-6M) and reserpine, EFS (50V, 1ms, 10Hz, trains of 3 min) induced significant (92.4±3.7;p<0.00002) transit relaxation in tissues per-contracted by 5-HTP. When 3x10-4M ADP was replaced to EFS, the contracted strips showed a sustained relaxation to relatively similar extent (78.8±3.5%; p<0.0035). However, administration of 3x10-4M L-NAME 10 min before addition of 5-HtP, was able to significantly reduce the relaxation induced by EFS to 13.8±0.9% and ADP to 39.6%±2.5 Addition of L-arginine (10-4M) to the medium, significantly reduced the L-NAME- induced contraction in the isolated tissues. The present study demonstrates the presence of NANC system in mice gastric fundus. This system may induce smooth muscle relaxation by ADP and NO synthesis. Vet.J.of Islam. Azad. Univ., Garmsar Branch. 1,3:41-45,2007

Keywords:

fundus , ADP , nitric oxide , non-adrenergic , non , colinergic