A note on the distribution of [c]-histamine added to blood.

(14)C-Labelled histamine was incubated with canine or human blood at 37 degrees C. After 1 hr 80 to 100% of the added histamine could be recovered in unchanged form. When [(14)C]-histamine was added to whole blood in vitro it tended to become equally distributed between the cell and plasma fraction of the blood, and when the cell fraction of blood containing [(14)C]-histamine was suspended in [(14)C]-histamine-free plasma the labelled histamine tended to become equally distributed between cells and plasma.

Metabolism of [c]-histamine in heart-lung-liver preparations of cats.

The metabolism of injected [(14)C]-histamine was studied in heart-lung-liver preparations and heart-lung preparations from cats. When the liver was included in the circulation the injected histamine was rapidly eliminated from the blood, some of its metabolites appearing in the blood within 2 min after the injection. More than 70% of the injected histamine was metabolized to 1-methylimidazol-4-ylacetic acid.

The effect of enzyme inhibitors on histamine catabolism in man.

The catabolism of histamine was studied in three female psychiatric patients by analysis of the [(14)C]-labelled metabolic products occurring in the urine after a subcutaneous injection of [(14)C]histamine. Each patient was studied before and during treatment with aminoguanidine or iproniazid.Without treatment the patients had a normal histamine catabolism.