[Dose-response pattern of inhaled sulfur dioxide (SO2) in rabbits pretreated with papain or sodium chloride aerosols].

The study was conducted on 29 New-Zealand female rabbits to examine the dose-response pattern of SO2 in inhaled air. A group of 14 animals was exposed to papain-aerosol (P-A) twice a week for 1 h each over 12 weeks in order to increase bronchial reactivity. A group of 9 animals received similar treatment but with saline-aerosol (NaCl-A); this group served for control. The third group of 6 animals remained untreated (K). After 12 weeks of treatment individual animals were anesthetized and the P-A and NaCl-A groups were exposed for 5 min each to different concentrations of SO2 (0.0, 1.0, 2.0, 4.0 and 9.0 mg/m3). The animals of group K were treated similarly but they were exposed 5X to synthetic air; this group served the purpose to follow the anesthesia effect on respiration and cardio-vascular system. The recovery period was 30 min between the exposures. The K-animals showed gradual decrease of lung resistance (R1). In contrast P-A and NaCl-A animals both showed a clear increase in R1 following exposure to SO2, and R1 was considerably higher in P-A than in NaCl-A animals. The maximum change in R1 was caused by exposure to 4.0 mg/m3 SO2 and it was even greater than the response produced by 9.0 mg/m3 SO2 in P-A animals. A similar pattern of response was also observed in NaCl-A animals, but the highest increase in R1 was caused by exposure to 2.0 mg/m3 SO2. From these results it can be concluded that high concentration of SO2 could have a damaging effect on sensory receptors of the tracheobronchial system.