Activity and distribution of histidine decarboxylase and histamine concentration in rat stomach.

The involvement of histamine in mediating gastric function under normal and pathological conditions has been largely established. Histidine decarboxylase (HDC) is the only synthetic enzyme of histamine in the mast cell or enterochromaffin like (ECL) cell. In this study, we examined, the activity of HDC by a method based on the modification of Kobayashi's method, the histological distribution of HDC containing cells was determined by an immunohistochemical method and the histamine concentration by a HPLC method in rat stomach. Histamine concentration in the total gastric layer of the fundus is overwhelming large compared to that in the antrum. On the other hand, histamine concentration of the mucosal layer of the fundus is 72.1 +/- 0.4 micrograms/g (mean +/- S.D.) and that in both the muscular and serosal layers is 7.2 +/- 0.4 micrograms/g. HDC activity of the total gastric layer of the fundus was about ten times as high as that in the antrum. Histological distribution of HDC-containing endocrine cells was observed in the basal part of the gastric mucosa of the fundus, but could not be observed in the muscular and serosal layer. These results suggest that HDC-containing endocrine cells, in only the basal parts of the mucosal layer of the fundus, were similar to ECL cells and have important parts for biosynthesis of internal gastric histamine. Therefore, using the total gastric layer of the stomach was thought to be easier than using only the mucosal layer for measuring gastric histamine and HDC-activity in rats.