Histamine turnover in rat brain

The half-life of histamine in the rat brain was measured by two independent techniques. Intravenous injection of inhibitors of histidine decarboxylase (brocresine or α-hydrazinohistidine) produced a prompt 20-25% depletion of histamine in hypothalamus and thalamus-midbrain. From the slope of the depletion curves, histamine in these regions was estimated to have a half-life of about 30 sec. A method was developed to estimate histamine half-life from the time course of [³H]histamine appearance following intraventricular injection of [³H]histidine. With this method, our data indicate a half-life for hypothalamic histamine of no more than about 1 min, much shorter than values in other parts of the body, where histamine turnover takes hours or weeks. By comparing the extent of reduction of newly synthesized [³H]histamine with that of endogenous histamine, it was determined that all histamine in the brain regions examined apparently lies within this rapidly turning over pool.