The effect of a respiratory tract infection on histamine-induced changes in lung mechanics and irritant receptor discharge in dogs.

The effects of intravenously administered histamine on total lung resistance (RL), dynamic lung compliance (Cdyn), and the discharge of lung irritant receptors have been measured in normal dogs and in dogs whose upper respiratory tract was naturally infected with the organism Bordetella bronchiseptica. The resting values for RL and irritant receptor discharge were similar for the infected and control dogs, but Cdyn was significantly lower in the infected group of dogs. Intravenous administration of 20 microgram of histamine/kg of body weight produced significantly greater direct and reflex changes in RL in the infected dogs than in the control animals. The changes in Cdyn in both groups of animals were similar. Intravenous administration of histamine (20 microgram/kg) produced a significantly greater increase in the rate of discharge of lung irritant receptors found in infected dogs than in control dogs. A possible mechanism responsible for the hyperreactivity to histamine is seen in the hypersensitivity of the irritant receptors introduced by the epithelial lesions observed in the infected dogs.