In 19 dogs sensitized against Ascaris suum extract we measured dynamic elastance, arterial plasma histamine concentration, pressure in the A. femoralis, and arterial blood gases. In six dogs the venous plasma histamine concentration was also analyzed.Ascaris extract (A.E.) inhalation increased both the arterial and the venous plasma histamine concentration significantly. The venous concentration was 61% of that detected in the arterial blood.At the same arterial plasma histamine level a large variety of dynamic elastance was measured which shows great individual differences in the sensitivity of the bronchoconstrictive system, This histamine released by the bronchopulmonary system works mostly via reflex bronchoconstriction.There was significant correlation between dynamic elastance and arterial oxygen pressure as well as between arterial plasma histamine concentration and systemic blood pressure.

Repeated ascaris extract (A.E.) exposure on dogs sensitized against this allergen at intervals of 90, 180, and 360 min is followed by different increases in the histamine concentration in the arterial plasma. At 90 min, a significantly smaller amount of histamine becomes measurable in the arterial plasma. Edyn increases unproportionally strong. One hundred eighty minutes after the first exposure A.E. inhalation is again followed by a clearly increased histamine concentration in the arterial plasma. Edyn still increases unproportionally strong. Three hundred sixty minutes after the first A.E. exposure another exposure revealed a stronger increase in the histamine concentration in the arterial plasma, the Edyn increase being smaller than at the first exposure. These results are of importance with regard to the sensitivity of the airways and the investigation of antiallergic and bronchospasmolytic drugs.