Turnover of different mast cell pools of histamine in the rat

The uptake and elimination of radiolabelled histamine was studied in the rat duodenum, where histamine is stored in a specific population of mucosal mast cells (MMC), and in the tongue, where histamine is stored in the classic connective tissue mast cell (CTMC). The specific activity of histamine was measured after one i.v. injection of its precursor, 3H-histidine. Decarboxylation of histidine and uptake of histamine occurred in both tissues. The initial specific activity of histamine was very low in the tongue but 5 times higher in the duodenum, while the endogenous duodenal histamine content was 1/6 of that in the tongue. The elimination rate of labelled histamine in the two mast cell pools was very slow. In the tongue, there was no statistically significant decrease in specific activity during the observation period of 16 days. In the duodenum, there was an exponential decrease of prelabelled histamine with an apparent half-life of 9 days. However, part of this decay of radioactivity may be accounted for by increase in the mucosal histamine pool size and MMC death. The results indicate that the rate of histamine elimination from mast cells of both types is very slow, corresponding with previous results obtained from CTMC of the peritoneal cavity.