Modification of bronchial blood flow during allergic airway responses

Ascaris suum antigen effects on mean airflow resistance (RL) and bronchial arterial blood flow (Qbr) were studied in allergic anesthetized sheep with documented airway responses. Qbr was measured with electromagnetic flow probes, and supplemental O2 prevented antigen-induced hypoxemia. Aerosol challenge with this specific antigen increased RL and Qbr significantly. Cromolyn sodium aerosol pretreatment prevented antigen-induced increases in RL but not in Qbr. Intravenous cromolyn, however, prevented increases in Qbr and RL, suggesting a role for mast cell degranulation in both bronchomotor and bronchovascular responses to antigen. Antigen-induced increases in Qbr were not solely attributable to histamine release. Indomethacin pretreatment attenuated the antigen-induced increase in Qbr, thus suggesting that vasodilator cyclooxygenase products contribute to the vascular response. Antigen challenge significantly decreased Qbr after indomethacin and metiamide pretreatment, which suggests that vasoconstrictor substances released after antigen exposure also modulate Qbr; however, released vasodilators overshadow vasoconstrictor effects. Thus antigen challenge affects Qbr by locally releasing histamine and vasodilator prostaglandins as well as vasoconstrictor substances. These effects were independent of antigen-induced changes in systemic and pulmonary hemodynamics.