Biochemical toxicology of unsaturated halogenated monomers.

Previous inhalation toxicity studies from our laboratory have shown that 1,1-dichloroethylene (1,1-DCE), 1,1-dibromoethylene (1,1-DBE), and 2-chloro-1,3,-butadiene (2-CBD) are more toxic to fasted rats than to fed rats. Vinyl chloride monomer (VCM) and 1,1-difluoroethylene (1,1-DFE) were not acutely hepatotoxic at 46,500 and 82,000 ppm, respectively, in normal male rats, whether fed or fasted. On a molar basis, 1,1-DBE and 1,1-DCE have similar toxicities while 2-CBD is less toxic. All three compounds produce similar elevation of serum transaminase and bloody ascites, although at differing times following differing exposure concentrations. 1,1-DCE produces massive midzonal hepatic necrosis with hepatic thrombosis and chromatolysis within 2 hr after a 4 hr exposure of fasted rats to 200 ppm. Subsequent to formation of this midzonal lesion, the central portion of the lobule collapses, accompanied by congestion, ascites, and in increased hematocrit in the rat. Serum transaminase and sorbital dehydrogenase are greatly elevated at 6 hr. This effect in fasted rats is associated with glutathione (GSH) depletion. Diethyl maleate (DEM) which depletes GSH in fed rats potentiates the injury associated with 1,1-DCE exposure as well as that produced by 2-CBD. Rats fed ad libitum and exposed to 1,1-DCE or 2-CBD at night, a time of low hepatic GSH concentration, exhibit enhancement of hepatotoxic response when compared to animals exposed during the day when GSH is high.