NONMAST-CELL HISTAMINE KINETICS .2. EFFECT OF HISTIDINE DECARBOXYLASE INHIBITORS ON RATES OF DECLINE OF TISSUE 3H-HISTAMINE IN FEMALE RAT

Inhibition of histamine synthesis in vivo was examined in terms of effects on the kinetics of decline of exogenous 3H-histamine in various tissues of the female rat. Inhibition of tissue histidine decarboxylase activity by dietary pyridoxine deficiency coupled with semicarbazide administration greatly reduced rates of decline in vivo of labeled amine. On the assumption that exogenous 3H-histamine equilibrates with endogenous amine in nonmast-cell pools, estimated rates of turnover of loosely bound histamine were reduced 30-75 per cent. The histidine decarboxylase inhibitor, NSD-1055 (4-bromo-3-hydroxybenzyloxyamine) was ineffective in reducing endogenous histamine levels and did not affect the kinetics of decline of 3H-histamine. It is suggested that the kinetics of 3H-histamine in vivo decline and the tissue histidine decarboxylase activity in vitro may reflect the same biochemical phenomenon-presumably the synthesis and catabolism of loosely bound nonmast-cell histamine in dynamic endogenous pools. © 1969.