Studies on the excretion of [14C]histamine and its metabolites by the rabbit kidney

1. After intravenous administration of [(14)C]histamine in rabbits, the urinary excretion of [(14)C]histamine and [(14)C]histamine metabolites was examined over a period of 4 hr.2. It was found that [(14)C]histamine was excreted in the unchanged form only in small amounts (6-7%), while 54-71% was eliminated in the form of its metabolites.3. Under normal conditions, the percentage excretion of metabolites, but not of histamine, showed a dose dependence. With the higher [(14)C]histamine dose, a significantly smaller proportion of the dose given was excreted as metabolites than with the lower dose. The proportion of unchanged [(14)C]histamine excreted remained constant.4. Pre-treatment with histamine infusions, or with mepyramine maleate, caused an increase in the excretion of [(14)C]histamine metabolites while the excretion of [(14)C]histamine remained unchanged.5. Pre-treatment with a diuretic, a combination of mersalyl and theophylline, did not influence the excretion of [(14)C]histamine nor of its metabolites.