Modulation by nitric oxide of spontaneous mechanical activity in rat proximal colon.

Summary 1 In order to examine the role of nitric oxide (NO) in the tonic neural inhibition in rat proximal colon, the effects of Nω-nitro- l-arginine methyl ester (L-NAME) were studied on the spontaneous contractions of circular muscle (monitored as intraluminal pressure changes) and of longitudinal muscle (detected as isometric tension changes). 2 L-NAME (3 × 10−−6–3 × 10−−4 m) caused a concentration-dependent increase in the amplitude of circular contractions, without affecting those of longitudinal muscle. This effect was prevented by l-arginine (1–5 × 10−−3 m), but not d-arginine. 3 In the presence of tetrodotoxin (10−−6 m), which per se induced increase of the pressure waves, L-NAME (1…