1. Following antrum exclusion the serum gastrin concentration was raised and independent of the prandial state. The antral gastrin concentration and number of gastrin cells were greatly lowered. 2. The histamine content and the number of histamine-storing endocrine ('entero-chromaffin-like') cells in the oxyntic mucosa was almost doubled and the mucosal histidine decarboxylase activity was greatly elevated following antrum exclusion. 3. At the ultrastructural level both types of histamine-storing endocrine cells (ECL and A-like) were found to be enlarged and to have a reduced number of granules per unit cytoplasm. These changes are compatible with an increased secretory activity. The G (gastrin) cells were not increased in size but their granule volume density was lowered. 4. We propose that antrum exclusion results in uninhibited gastrin release causing profound changes in the histamine-storing endocrine cells of the oxyntic mucosa. The cells respond to the hypergastrinemia by an increase in functional activity (activation of histidine decarboxylase and reduction of granule volume density) as well as by an increase in number and size.
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