Histamine formation in guinea-pig brain and other tissues: Effect of α-methyl dopa

Pretreatment of guinea pigs with -methyl-l-dopa, an inhibitor of a non-specific decarboxylase, followed by injection of¹⁴C-l-histidine, had little effect on¹⁴C-histamine tissue levels relative to controls. Since earlier longterm tests showed that comparable doses of inhibitor markedly reduced urinary¹⁴C-histamine, it is tentatively concluded that the non-specific enzyme decarboxylatesl-histidine primarily in kidney, at a site from which newly-formed histamine is excreted directly, without entering the blood stream.¹⁴C-histamine levels in brain were relatively high and provide the strongest available evidence that histamine is formed in brain under physiological conditions.Supported by NIH Grant AM-10155.