Absorption of paraquat and diquat from the airways of the perfused rat lung.

The uptake of paraquat dichloride (bis-N-[14C]methyl-4,4'-bipyridilium chloride) and diquat dibromide (N,N-ethylene-[U-14C]2,2'-bipyridilium dibromide monohydrate) from the airways and by the vasculature of the isolated and perfused rat lung (IPL) were studied. A semilogarithmic plot of the percent unabsorbed with time revealed a bi-exponential decay, suggesting at least two phases of removal of paraquat and diquat from the airways. The rapid initial process was similar for both herbicides. The slow component had at t1/2 of 355.98 min for paraquat and 75.03 min for diquat. This second process may represent the storage pool associated with the pulmonary toxicity of paraquat. When paraquat or diquat was presented to the capillary side of the lung, long-term storage was not evident. Uptake by the lung occurred from the pulmonary circulation with similar velocity. These data suggest that the energy-dependent uptake observed with lung slices probably represents airway transport and may be associated with cell membranes lining the alveolus.