The importance of the diluent for airway transport of toluene diisocyanatefollowing intranasal dosing of mice

Uncertainty of the transport of reactive chemicals to the lung is a major c oncern when using intranasal dosing of animals. In a preliminary study usin g mice, intranasal instillation of the dyes methylene blue (in water) and S udan black B (in 1:4 ethyl acetate:olive oil), indicated that the following conditions were necessary to achieve transport to the lung: (1) aqueous di luent, (2) light anesthesia prior to dosing, (3) holding the animal in a su pine position during chemical application, and (4) maintaining the animal i n the same position postdosing. Using these conditions, we investigated the distribution of toluene diisocyanate (TDI), a major industrial asthmogen, to the lung following intranasal administration. Female C57BL/6 mice receiv ed 20 mu l of 1% TDI in ethyl acetate:olive oil (1:4). Group 1 received a s ingle application on day I; group 2, single applications on 2 consecutive d ays; group 3, single applications on 3 consecutive days; and group 4, a sin gle application of the vehicle on 2 consecutive days. Ail mice were necrops ied 24 h after the final application. The nasal passages, upper pharynx, tr achea, lungs, and olfactory bulbs of each animal were examined with hematox ylin-eosin and immunohistochemical staining, the latter using a rabbit anti -TDI antiserum. Histopathology revealed desquamation of ciliated epithelial cells as weil as inflammatory cell debris in the nasal cavity and upper ph arynx of animals in groups 1-3. The intensity of these changes was dependen t on the number of applications. No inflammation was observed in the trache a, lungs, or olfactory bulbs in any of the groups. Immunohistochemical exam ination revealed positive staining for the TDI moiety in epithelial cells o f the nasal cavity and upper pharynx in animals of groups 1-3. No staining was observed in the trachea, lungs, or olfactory bulbs of any animal. These results suggest that TDI, when dissolved in olive oil:ethyl acetate and ap plied intranasally, does not reach the trachea and/or lower airways.