Metabolism of 14C-histamine given intrabronchially to asthmatic patients

14C-histamine was administered intrabronchially to asthmatic patients and controls. The urinary excretion of total radioactivity, 14C-histamine and its radioactive metabolites was measured. It was found that the excretion of total radioactivity was complete within 24 h. The excretion rate was equal to that observed after intravenous injection of 14C-histamine, indicating a rapid penetration of the bronchial mucosa. However, the diuresis seemed to be of importance for the excretion rate. Histamine inactivation by methylation was more pronounced after intrabronchial than after intravenous administration.