Histamine releasers and rat mast cells.

The release of histamine from rat tissues rich in mast cells, induced by antigen, concanavalin A, dextran, compound 48/80, A 23187, phosphatidic acid and chlortetracycline, has been compared with that from isolated peritoneal mast cells of rats. Whereas most of the agents were more active than dextran in in vitro experiments, the reverse was found when they were injected intradermally into the skin, or subcutaneously into the paws. In fact, A 23187 and chlortetracycline (both calcium ionophores), as well as phosphatidic acid (another non-cytotoxic releaser), failed to release significant amounts of histamine when injected into the animal. Thus, the experimental conditions in which comparisons of the activities of histamine releasers are made should always be stated.