Differences in the effects (in vitro) of ethylenediamine on the guinea-pig and rat intestine.

The effects of ethylenediamine in different regions of the rat and guinea-pig small intestine were investigated pharmacologically using isolated gut-bath preparations. In the guinea-pig, ethylenediamine caused concentration-dependent neurally mediated contractions or biphasic responses (contraction followed by relaxation). The contractions could be prevented by muscarinic and GABAA receptor antagonists. Ethylenediamine-evoked relaxations and depression of electrically evoked cholinergic twitch responses were blocked by desensitization to baclofen. However, in the rat intestine, the primary response to applied ethylenediamine was a concentration-dependent, non-desensitizing relaxation, evidently due to a direct action of ethylenediamine on the muscularis since it was unaffected by tetrodotoxin or GABAergic blockade.