Histamine and microcirculation

Recent research of histamine metabolism suggests that microvascular smooth muscle and endothelial cells are under the continuous dilator influence of minute quantities of intrinsically formed histamine, produced by action of an inducible form of histidine decarboxylase. Various autonomous dilator activities of the microcirculation, e.g., vasomotion, reactive and post- exercise hyperemia and autoregulation, may all involve interplay of this intrinsic dilator with an intrinsic constictor mechanism. Drastic stimuli which cause a marked increase in histamine output locally or systemically, may lead to the early, slowly-developing microvascular changes in inflammation and shock, respectively.