Novel accessory skull bone in fetal rats after exposure to aspirin.

Aspirin was administered by oral gavage to 25 gravid Sprague-Dawley rats on gestation day 10, as a single dose of 500 mg/kg, in a concentration of 50 mg/ml. The aspirin was suspended in a mixture of 0.5% w/v hydroxypropylmethylcellulose (Methocel E-4M) and 0.1% w/v polysorbate 80 (Tween 80). A control group of 25 gravid rats was given 10 ml/kg/day of the suspending vehicle alone, by oral gavage, on gestation days 6 through 15. C-sections were performed on gestation day 20. Approximately two-thirds of the fetuses were processed for skeletal examination with Alizarin Red S; the remaining fetuses were placed in Bouin's solution. Examination of the fetal skeletal specimens from the aspirin-treated group revealed a 20% fetal (43% litter) incidence of an accessory skull bone, located between the nasal and frontal bones. This structure ranged in size from a small, barely discernible, circular ossification site (less than 0.5 mm) to a relatively large, bilobate bone (approximately 2 mm). This anomaly has not been previously reported in fetal rats.