NITRIC-OXIDE CAUSES CONTRACTION IN THE RAT ISOLATED SMALL-INTESTINE

The effect of authentic nitric oxide (NO) was investigated on rat ilea l myenteric plexus-longitudinal muscle strips in the presence of atrop ine. NO (10-(10) to 3 x 10(-6) M) caused a quick, transient contractio n of the smooth muscle, with an optimum concentration of 10(-7) M, as well as a slower contraction with a higher optimum concentration. In p reparations sub-maximally pre-contracted with 5-hydroxytryptamine, NO (10(-7) to 3 X 10(-6) M) also caused a quick relaxant response. These responses to NO (10(-6) M) were not influenced by tetrodotoxin, indica ting a direct effect on the smooth muscle.