Histamine hyperresponsiveness with viral bronchiolitis may depend on previous exposures to viruses or to other pathogens. We studied 32 outbred beagle pupples 80 to 155 days of age who were raised in isolation and who were specific pathogen-free. Pupples were inoculated with canine parainfluenza type 2 (CPI2, n = 8), Bordetella bronchiseptica (Bb, n = 7), or both CPI2 and Bb (CPI2-Bb, n = 9). Control puppies (C, n = 8) were not inoculated. The puppies were anesthetized with sodium thiopental (5 mg/kg) and chloralose (80 mg/kg) and were ventilated mechanically. Lung resistance (RL), dynamic lung compliance (Cdyn), functional residual capacity (FRC), and responsiveness to aerosolized histamine were measured 3 days prior to inoculation (Day -3), on the day of inoculation (Day 0), and on Days 3-4, 6, 8-10, and 12-14 after inoculation. Histamine responsiveness was measured as: (1) the concentration of histamine base that increased RL to 150% (PC 150% RL) or decreased Cdyn to 75% (PC 75% Cdyn) of the response to saline (RL sal and Cdyn sal, respectively), and (2) the change in RL or Cdyn after inhalation of 11 mg/ml of histamine when compared with RL sal and Cdyn sal. On day 0 there were no significant (p > 0.05) differences among groups with regard to age-corrected weights, FRC, RL, Cdyn, or histamine responsiveness. Control puppies remained healthy, and their pulmonary function and histamine responsiveness did not change. CPI2-Bb puppies increased RL and decreased FRC on Day 3-4, and were moderately ill and histamine-hyperresponsive on Day 3-4 and on Day 6. CPI2 puppies were mildly ill and had increased histamine responsiveness only on Day 6. Bb puppies were mildly ill, but they were not histamine-hyperresponsive. By Day 12-14 all puppies were asymptomatic. Their pulmonary function and histamine responsiveness had returned to baseline (Day 0) and were not significantly different among groups. Thus, CPI2 and CPI2-Bb bronchiolitis increased histamine responsiveness, which paralleled the severity and duration of the acute illness in previously uninfected beagle puppies.
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine