Increased levels of histamine observed in the skin of adrenaline-treated rats or mice are not the result of histamine synthesis by mast cells.

Like the skin of rats and mice injected with adrenaline (AD), rat isolated peritoneal mast cells display increased levels of perchloric acid-soluble histamine following incubation with AD. Although pre-exposure to alpha-fluoromethyl histidine (FMH), an inhibitor of histidine decarboxylase, prevented the effect of AD in vivo and in vitro, this compound was also found to inhibit mast cell granule swelling evoked by AD, a response linked to histamine changes. Absence of increased levels of isotopic histamine in mast cells incubated with labelled histidine in the presence of AD, as well as the insufficient amounts of would-be precursor histidine found in untreated mast cells, confirm the conclusion that AD does not increase mast cell histamine by stimulating its synthesis.