Contraction of the colon induced by intra-aortic injection of cholinomimetic agents: a procedure for estimating spasmolytic activity in the anaesthetized rat.

An in vivo model for evaluating spasmolytic activity in the anaesthetized rat has been developed. A peculiarity of this model is the injection of parasympathetic agonists directly into the abdominal aorta. Acetylcholine and carbachol produced constant contractions of the ascending colon, while the cardiovascular system was affected only to a small extent. The contractions could be selectively antagonized by antimuscarinic drugs administered by either intravenous or intraduodenal route. Antagonists at other receptor systems were ineffective. The present procedure provides a reliable test model which mimics, in the rat, the technique of close intra-arterial injection of spasmogen feasible only in bigger animals.