The comparative absorption and excretion of chemical vapors by the upper, lower, and intact respiratory tract of rats.

Upper respiratory tract (URT) absorption of several compounds with differing water solubilities and potentials to cause lesions of the nasal mucosa were studied in rats. Absorption of propylene glycol monomethyl ether (PGME), PGME acetate (PGMEAc), ethyl acrylate (EA), epichlorohydrin (EPI), styrene (STY), nitroethane (NE), ethylene dibromide (EDB), and methylene chloride (MeCl2) vapors by the isolated URT was compared to that by the isolated lower respiratory tract (LRT) and the intact animal. Nearly all PGME and PGMEAc and 30-70% of EA, EPI, STY, NE, and EDB were absorbed when passed through the URT. In general, similar levels were absorbed by both the isolated LRT and intact animal. It was estimated that intact animals received more than 90% of their total dose of PGME and PGMEAc, and 50% of EA, NE, EPI, and EDB via the URT. Further, the dosage per unit of surface area in the URT may be 5000-6000 times that of the LRT. However, the extent of URT absorption was not related to the ability to cause lesions of the nasal mucosa. Absorption of compounds by the URT was not a simple function of water solubility or of blood or water/air partitioning coefficients suggesting that a more complex mechanism for controlling absorption may exist. In one case, it was demonstrated that URT enzymatic activity could influence the absorption of certain compounds by the URT.