Role of nitric oxide in the peristalsis in the isolated guinea-pig ileum

The role of nitric oxide in peristalsis was studied by using N G - nitro- L-arginine , an inhibitor of the biosynthesis of nitric oxide, in the isolated guinea-pig ileum. Constant peristalsis was cyclically induced by distending the ileal wall with intraluminal solution infused at a constant rate. N G - Nitro- L-arginine (10 −6 to 10 −4 M) dose dependently increased the frequency of peristalsis. This effect of N G - nitro- L-arginine was almost hindered by pretreating the ileum with 10 −3 M L-arginine, but not D-arginine. Nitroprusside (5 × 10 −7 M) reversed the frequency increase. In the presence of N G - nitro- L-arginine , peristalsis propulsion occured at a smaller distension of the ileal wall and the ileum constricted to a smaller diameter at the completion of propulsion. The rate of shortening of longitudinal muscle during distension was raised by N G - nitro- L-arginine , although the peak magnitudes were not changed. Consistent with these effects of N G - nitro- L-arginine on peristalsis, N G - nitro- L-arginine at 10 −5 M increased the contractions of circular muscle in response to electrical field stimulation, but not those of longitudinal muscle. These results suggest that endogenous nitric oxide modulates peristalsis by limiting the contractile activity of the circular muscle of the guinea-pig ileum.