Effects of dinocap on otolith development: Evaluation of mouse and hamster fetuses at term

Abstract The morphology of otoliths in CD‐1 mouse and Syrian hamster fetuses exposed to the fungicide dinocap were evaluated at the end of gestation. Pregnant mice were dosed by gavage with 0, 10, 15, 30, or 60 mg/kg/day dinocap in corn oil on days 7–16 of gestation. Pregnant hamsters were dosed by the same route with 0, 50, 100, or 200 mg/kg/day on days 7–14 of gestation. At the end of gestation (day 18 in mice, day 15 in hamsters) dams were killed and all fetuses were removed and fixed overnight in 70% ethanol. Fetal heads were then removed, left in 70% ethanol for at least 3 days, and then dehydrated in a graded ethanol series and cleared with methyl salicylate. Otoliths were examined by darkfield microscopy, and each otolith was scored for morphological completeness on a scale of 0 to 3. Otolith development was complete by day 18 of gestation in control mouse fetuses. Otolith development was complete in many, but not all, of the hamster fetuses by day 15 of gestation. In the mouse, dinocap exposure inhibited fetal otolith formation in a dose‐related manner, with a significant effect on total otolith score occurring at 10 mg/kg/day and above. Dinocap affected otolith formation in the hamster only at 100 mg/kg/day (200 mg/kg/day was embryolethal), concommitant with severe maternotoxicity and fetotoxicity. The results of this study indicate that the CD‐1 mouse is more sensitive than the Syrian golden hamster to the effects of dinocap on otolith development, and that otolith morphology can be easily examined in the mouse and hamster fetuses at term, although not by techniques currently used for fetal examination in standard teratology bioassays (e.g., Segment II studies).