Histamine content of peritoneal and tissue mast cells of growing rats.

The histamine and 5-hydroxytryptamine (5-HT) content of mast cells was measured in rat peritoneal mast cells (isolated by density-gradient centrifugation or in crude peritoneal cell suspensions) and in some solid, mast-cell-rich tissues (tongue, skin, and duodenum). The duodenum contains large numbers of mast cells belonging to the specific type of mucosal mast cell. The peritoneal cavity, tongue, and skin contains the classical, mature connective-tissue-type of mast cell. The approximate amine content in mast cells of solid tissues was calculated by combining the biochemical assays with cell counting. The amine content was related to the age and body weight of the rats, studied during a period of rapid body growth (25-233 days). In the connective-tissue-mast cells both amines showed an increase that was strongly correlated to age and body weight. The increment of histamine was not as large as that of 5-HT. In peritoneal mast cells the histamine content per cell was doubled during the growth period studied, whereas there was a sixfold increase of 5-HT. The estimated 5-HT content per mast cell of tongue and skin also increased in relation to body weight. The histamine/5-HT quotients in these tissues were similar, and decreased with increasing age as did the same quotients for peritoneal cells. Parallel cell counts and histamine assays indicated that the mucosal mast cells contained much less histamine than the connective-tissue mast cells, and this findings was supported by histochemical observations. The observations did not suggest that histamine is stored else-where than in mast cells. In the mucosal mast cells, too, the histamine content appeared to increase as a function of age and body weight. Duodenal 5-HT, which is to a large extent contained in enterochromaffin cells, did not increase in relation to body growth.