Concentration of histamine in different parts of the brain and hypophysis of rabbit: effect of treatment with histidine, certain other amino acids and histamine.

1. Estimates have been obtained by biological assay of the histamine concentration in different parts of the rabbit brain and hypophysis.2. Mean values (ng/g) for the brain were: hypothalamus, 660; central grey matter and medial thalamus, 275; tegmental region of mid-brain, the hind-brain and caudate nucleus, 140 to 170; hippocampus and cerebral cortex, 90 to 110; cerebellum (vermis), 60.3. The mean value (ng/g) for the anterior lobe of the hypophysis was 650; for the posterior lobe, 400.4. In conscious rabbits, intravenous infusion of histidine in the dose range 62 to 1,500 mg/kg, raised significantly (P<0.01) the concentration of histamine in all regions of the brain examined, the pattern of distribution remaining unchanged. The largest increases occurred in the mid brain (90 to 320%) and in the hypothalamus (50 to 250%); in these areas the higher doses produced higher concentrations. Elsewhere in the brain the concentration rose in response to the lowest dose of histidine, but was not increased when higher doses were given. Concentrations in the anterior lobe of the hypophysis were unaltered.5. The infusion of histidine, unlike that of amino acid precursors, of the monoamines, produced no obvious disturbance in the animals.6. The rise in brain histamine after dosage with histidine persisted for several hours, depending on the dose; with 500 mg/kg, the rise was virtually unchanged after 16 hours.7. Histamine (5 mg/kg by intravenous infusion) raised the concentration of histamine in the hypophysis but not in the brain.8. After the infusion of DOPA, alpha-methyldopa or 5-hydroxytryptophan, the histamine concentration rose in the mid-brain but not in other parts of the brain.9. These amino acids, when infused singly with histidine, did not interfere with the histidine-induced rise of brain histamine.