Rings of whole ileum or mucosal scrapings from clinical cases of Johne's disease, or from subclinically infected animals, accumulate L-histidine at considerably less than the normal rate when incubated in Krebs-Ringer bicarbonate solution containing this amino acid at a concentration of 20 mM. “ Active ” uptake of histidine against a concentration gradient can be abolished by the addition of 0·2 mM-2:4-dinitrophenol to the incubation medium. The proportion actively accumulated was about 61 per cent. in normal mucosal scrapings, but only some 25 per cent. in specimens obtained from clinically affected cattle.

In the same tissue preparations, the mean total rate of histidine accumulation was almost halved, but its passive uptake was virtually unaffected, indicating that, in infected cattle, histidine probably diffused into the mucosal cells normally. By direct microscopic measurement, it was found that the thickness of the mucosal tissue layer in the ileum was not significantly greater in clinically affected cattle than in healthy controls. The weight of ileum per unit length, however, was, on the average, increased almost four times on account of massive submucosal infiltration.

It is suggested that the marked reduction in the “ active ” uptake of histidine by the mucosa from infected animals is indicative of a malabsorption state. The part this factor plays in the pathogenesis of the terminal clinical phase of Johne's disease is discussed.


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