Histamine enhances anaphylactic histamine release from bovine lung and leukocytes via histamine H2-receptor

Chopped lung and isolated leukocytes of calves sensitized to horse plasma release histamine when incubated with the antigen. Low concentrations (10(-9) and 10(-8) M) of exogenous histamine enhanced both spontaneous and antigen-induced histamine release. The enhancement of antigen-induced histamine release was inhibited by metiamide but not by mepyramine, whereas the enhancement of spontaneous histamine release was not significantly affected by either histamine antagonist. At higher concentrations of exogenous histamine (10(-6) to 10(-4) M), uptake and metabolism significantly interfered with the method. These results indicate the existence in bovine lung and leukocyte of a positive feedback mechanism which regulates histamine release via an H2-receptor. This is in direct contrast to the reported situation in the human leukocyte, and suggests that histamine fulfils an important role in the intrinsic control of allergic reactions in cattle.