IN-VITRO ALLERGIC BRONCHOCONSTRICTION IN THE BROWN-NORWAY RAT

The ovalbumin (OA)-sensitized Brown Norway rat (BN) demonstrates early-response (ER) and late-response (LR) allergic bronchoconstriction. To determine whether these responses could be replicated in vitro, we studied lung explants from 8-wk-old male BN rats (wt: 239 +/- 28 g), of which 19 were sensitized to OA (test) and 16 served as controls. Two weeks after sensitization, the animals' lungs were removed, filled with a 1% (wt/vol) agarose-containing solution at 37 degrees C, and cooled to 4 degrees C. Transverse slices (0.5 to 1.0 mm thick) were cut and cultured overnight. Airways were visualized with an inverted microscope and baseline images were obtained with a video camera. To study the ER, 40 airways from 15 test rats and 29 airways from 10 control rats were challenged with 2 mu g OA and imaged each minute for 10 min. To study the LR, 40 airways from 12 test rats and 44 airways from 12 control rats were challenged with 2 mu g OA and imaged each hour for 8 h. The maximal response (MR) for each airway was defined as the percent of airway closure. The ER and LR were both defined as an MR greater than or equal to mean + 2 SD of the controls. An ER occurred in 38 of 40 test and 2 of 29 control airways (mean MR: 42 +/- 24% versus 4 +/- 3%, p < 0.001), and was completely blocked by methysergide pretreatment in 13 airways. An LR occurred in 18 of 40 test and four of 44 control airways (mean MR: 18 +/- 21% Versus 4 +/- 4%, p < 0.05), and was partially blocked by pretreatment with the leukotriene D-4 (LTD(4)) antagonist MK-571 in 16 airways. In the BN rat, the ER is mediated by serotonin. The LR is partially leukotriene-mediated and occurs in the absence of de novo inflammatory cell recruitment.