Gastrins and cholecystokinins release acetylcholine but not substance P from neurons in the guinea-pig taenia coli.

Gastrins and cholecystokinins contract the isolated taenia coli of the guinea-pig. Porcine CCK-39 produced the greatest contractile response and human gastrin-17 I and -34 the weakest. Pentagastrin had the highest affinity to the receptors and non-sulphated CCK-8 the lowest. The contractions produced by the CCK peptides were reduced by the neuronal blocker tetrodotoxin and by the muscarinic blocker atropine but not by the substance P antagonist [D-Pro2,D-Trp7,9]SP. It is concluded that gastrin/CCK peptides act directly on smooth muscle cells and that in addition these peptides, notably sulphated forms of CCK, are capable of exciting cholinergic neurons (but not SP neurons) to cause smooth muscle contraction.