Structures Essential for the Effect of Cholecystokinin on the Guinea Pig Small Intestine in vitro

Abstract

The stimulating effect of cholecystokinin on the small intestine was investigated by different registration techniques in the guinea pig ileum in vitro. The effect of cholecystokinin was blocked by atropine, morphine and tetrodotoxin but not by hexamethonium or pretreatment with reserpine. Cholecystokinin was still effective after desensitization to 5-hydroxytryptamine. After a propagated contraction in the circular muscle layer induced by an increased intraluminal volume or by 5-hydroxytryptamine there was a refractory period for 20—60 sec which could not be registered when the corresponding response was induced by cholecystokinin. It is concluded that the stimulating effect of cholecystokinin on the two muscle layers of the guinea pig small intestine is mediated via a cholinergic neural pathway without cholinergic synapses. The mechanism of action is still unknown but does not seem to consist in a release of 5-hydroxytryptamine.