Haemophilus influenzae induces a potentiated increase in guinea-pig pulmonary resistance to histamine.

The human respiratory pathogen Haemophilus influenzae (H.i.) induced bronchial hyperreactivity to histamine (1.0-8.0 micrograms/100 g b.w. i.v.) in vivo in anaesthetized spontaneously breathing guinea-pigs. This hyperreactivity was caused by a potentiated increase in pulmonary resistance. Decreases in dynamic compliance did not differ. Atropine prevented the potentiation at 1.0 and 2.0 micrograms histamine/100 g b.w. These results show that H.i. induces bronchial hyperreactivity in vivo which is mediated by direct and reflex effects of histamine in the central airways.