Involvement of cholinergic neurons in intestinal contraction caused by vasoactive intestinal contractor.

The mechanism of the contractile response to vasoactive intestinal contractor (VIC) was examined in the isolated guinea-pig small intestine. VIC at 10(-9) to 10(-7) M produced a transient relaxation followed by a contraction, and this contraction was partially inhibited, to the same degree, by either atropine or tetrodotoxin. VIC (10(-8) M) induced an increase in the release of [3H]acetylcholine from the ileum preloaded with [3H]choline. The VIC-induced acetylcholine release was dependent on external Ca2+. Thus, the VIC-induced contractions may relate to stimulation of cholinergic neurons and smooth muscle cells.