Effects of exogenous and endogenous histamine on the respiratory system.

There is a statistically strong correlation between the increase of the histamine concentration in the arterial plasma and the increase of airway resistance. The histamine causes a reflex bronchoconstriction on the sensory receptors. Histamine in low concentration increases the unspecific reaction in the bronchial system. This can also be achieved using low concentrations of allergen aerosols. Patients with chronic obstructive bronchitis show high concentrations of histamine in the sputum. The bronchoconstrictive potency of this histamine was found to be not always active. Higher concentrations of histamine can be liberated by washing the inner surface of the bronchial tree. Histamine injected in similar concentrations as that measured in the sputum causes bronchoconstriction. There should be high concentrations of histamine receptors as well as mast cells near the surface of the mucosa of the bronchial wall. There are many questions remaining open, which will be discussed.