EFFECT OF A RESPIRATORY-TRACT INFECTION ON HISTAMINE-INDUCED CHANGES IN LUNG-MECHANICS AND IRRITANT RECEPTOR DISCHARGE IN DOGS

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Abstract
Effects of i.v. administered histamine on total lung resistance (RL), dynamic lung compliance (Cdyn) and discharge of lung irritant receptors were measured in normal dogs and in dogs whose upper respiratory tract was naturally infected with the organism Bordetella bronchiseptica. Resting values for RL and irritant receptor discharge were similar for infected and control dogs but Cdyn was significantly lower in infected dogs. Administration i.v. of 20 .mu.g of histamine/kg of body wt produced significantly greater direct and reflex changes in RL in infected dogs than in control animals. Cdyn changes in both groups of animals were similar. Administration i.v. of histamine (20 .mu.g/kg) produced a significantly greater increase in rate of discharge in lung irritant receptors found in infected dogs than in control dogs. A possible mechanism responsible for hyperreactivity to histamine is seen in the hypersensitivity of the irritant receptors introduced by epithelial lesions observed in infected dogs.