Distribution of histamine and substance P in the wall of the dog's digestive tract / by W.W. Douglas [and others].

Date:
[1951?]
Catalogue details

Licence: In copyright

Credit: Distribution of histamine and substance P in the wall of the dog's digestive tract / by W.W. Douglas [and others]. Source: Wellcome Collection.

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    histamine equivalents than those of the gl. mucosae. The reduction in the histamine content of the wall from duodenum to ileum is shared by all layers except the m. mucosae, so that, in the lower part of the ileum, the m. mucosae is many times richer in histamine than any other layer. The gradient in the histamine content from duodenum to ileum is in part also accounted for by the fact that the m. externa presents a higher percentage of the wall in the ileum than in the duodenum. The relatively high histamine content of the submucosa is not derived from the adjacent muscularis mucosae by diffusion during the delay in extraction, as shown by the following experiment. A loop of duodenum was opened under chloralose anaesthesia. The mucosa and the m. mucosae were scraped away from the submucosa, allowing the blood to flow freely during this time, and leaving the submucosa in contact only with the histamine-poor m. externa. The portion of duodenum was then excised and the submucosa dissected off and extracted. Its histamine content was 60p,g./g., as compared with 65p,g./g., the histamine content of an adjacent piece of sub mucosa prepared with the usual technique. In Expt. 1, the m. externa from the piece lying between nos. 6 and 7 was separated into its two layers, which were extracted separately. The tissue of the circular muscle layer made up two-thirds of the wall and contained 41pg./g. histamine, whereas the longitudinal muscle layer with serosa con¬ tained 23pg./g. The value for the m. externa calculated from these figures would be 35/xg./g., which has to be compared with 42 and 34/zg./g., the cor¬ responding values found for the m. externa in the adjacent pieces. Colon and rectum. The histamine values of colon and rectum are lower than those of the lower ileum. The histamine gradient in the small intestines thus continues in the colon and rectum. Only a thin layer of gl. mucosae could be scraped off, and this layer contained very little histamine. No histological examination was made to see if the remainder of the mucosa was free from glandular tissue and consisted solely of m. mucosae; it certainly had a hista¬ mine content as high as that of the m. mucosae of the small intestine, whereas the thick m. externa, with a histamine content of 7—18 /xg./g. contributed 7-22% of all histamine of the wall. Presence of an unidentified smooth muscle stimulating substance (substance P) in extracts of the wall of the digestive tract. When the atropinized ileum preparation was made insensitive to histamine by mepyramine, amounts of extract which had previously caused contraction became inactive, but if the dose of extract was increased five to tenfold, some of the extracts again caused contractions which developed more slowly than those previously produced. These slow contractions were not due to histamine