Distribution and Intensity of Monoamine Oxidase Activity in the Mammalian Duodenum

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Abstract
The quantity and localization of monoamine oxidase (MAO) activity was studied in the duodenum of eight mammalian species.There were great differences in the enzyme activity between various species.In the guinea pig, the rabbit and the mouse MAO activity was 6–9 times as high as that in the rat, the cow, the pig and the horse.The sheep differed significantly (P<0.001) from all other species.In the pig, the activity of the muscular layers was about a third of that observed in the united mucous and submucous layers.Histochemically the epithelium adjacent to the intestinal lumen showed a strong enzyme activity in all the species but the cow, the sheep and the rat.The Brunner glands and the muscular coats exhibited a moderate or weak reaction.The serosa and mucous muscular layer were negative.The results are compared with those made by the present author on the distribution of 5‐HT and the enterochromaffin cells in the same species.There is no correlation between chemically estimated MAO activity and 5‐HT content in the duodenum.The histochemical distributions of the enzyme activity and 5‐HT are also different.