Amine Formation by Rat Mast Cellsin vitro

The effects of incubation temperature, time, pH, cell concentration, pyridoxal and aminoguanidine on 14 C histamine formation by rat mast cells in vitro were investigated. It was shown that disruption of the cells by physical means (sonication, freezing and thawing and hypotonic shock) or treatment with the histamine releaser ATP caused a marked reduction in histamine formation. In contrast to this, treatment of the cells with compound 48/80 caused an increase in histamine formation. After water lysis and centrifugation the histidine decarboxylase activity was found predominantly in the non‐particulate fraction. The cells were also shown to decarboxylate 5HTP and dopa in vitro , forming 5HT and dopamine. Hydroxylation of phenylalanine, tyrosine or tryptophan could not be demonstrated. This suggests that the reason why normal rat peritoneal and pleural mast cells contain relatively low amounts of 5HT (compared to histamine) and no dopamine is the unavailability of the immediate precursors (5HTP and dopa) and their inability to synthesize these by hydroxylation of tryptophan or tyrosine.