Stimulation by epinephrine of histamine synthesis by rat peritoneal fluid mast cells in vitro

In vitro exposure of mast but not of other cells of rat peritoneal fluid to epinephrine leads, within 1 min, to progressing levels of histamine in both fluid and sedimentable phases of the incubates, which present no increase in their free/total histamine ratio. Histamine increase was blocked by alpha-fluoromethyl histidine (alpha FMH), acting after a significant lag period. When compared with controls under the electron microscope, epinephrine-treated mast cells show less electron-dense, swollen intracellular granules, apparent maintenance of cell membrane continuity and an apparent decrease of peripheral finger-like projections. Histamine accumulation by epinephrine-treated mast cells may be the result of an enhanced ability of pre-formed mast cell histidine decarboxylase to attack its cell-borne substrate, consequent to an unfolding of the cell membrane during cell tumefaction evoked by epinephrine.