Histamine release from isolated and intact mast cells of rats

The release of histamine from tissues of rats, induced by antigen, concanavalin A and dextran has been compared with that from isolated peritoneal mast cells. Whereas concanavalin A was more active than dextran in in vitro experiments, the reverse was found when the substances were injected intradermally into the skin or subcutaneously into the paw. Therefore, it is important to state the experimental conditions when comparisons of activities of histamine releasers are made.