Nitric oxide induces acetylcholine-mediated contractions in the guinea-pig small intestine.

In longitudinal muscle/myenteric plexus preparations of the guinea-pig ileum, exogenous nitric oxide (NO) induced concentration-dependent relaxations. In tissues at basal tone, NO (3 x 10(-6) M) induced a moderate relaxation followed by a pronounced contraction, consisting of a quick and sustained component. Tetrodotoxin (5 x 10(-7) M) abolished both phases of the contraction. Atropine (5 x 10(-7) M) abolished the quick component and reduced the sustained component of the contraction; the latter was further suppressed by the selective NK1 receptor antagonist CP 96,345. Hexamethonium (5 x 10(-5) M) failed to affect the contractile response to NO. It is concluded that administration of exogenous NO in the guinea-pig ileum can lead to activation cholinergic and to a lesser degree tachykininergic neurones.