Mirex-induced fetal cataracts: lens growth, histology and cation balance, and relationship to edema.

The effects of mirex on growth, histology, and K+ and Na+ concentrations of the fetal lens are examined. Pregnant Long-Evans rats were intubated with 6 mg/kg/day mirex in peanut oil on days 8-15 of gestation. Control dams received pure peanut oil. Fetuses were removed on days 18-21 and rated for extent of lens opacification and degree of edema. Lenses were removed, weighed, and assayed for K+ and Na+. Selected eyes were examined histologically. Cataracts were found in 49.6% of live treated fetuses on day 20, and the incidence and severity of cataracts were both correlated with the degree of fetal edema. Lens weights were reduced in treated litters whether or not cataracts occurred, but the reduction in cataractous lenses was greater. Sodium tended to be elevated and K+ reduced in lenses from treated fetuses, and the K+/Na+ ratio was significantly reduced in all treated groups. Histologically, treated lenses had swollen fibers on day 18 and areas of apparent cell breakdown by day 20. The swollen lens fibers, reduced K+/Na+ ratios and the correlation with edema suggest that fetal cataracts induced by mirex may be due to lens fiber cell breakdown subsequent to osmotic swelling.