0 ginal Susceptibility of Day − 12 . 5 and Day − 13 . 5 Fetal Mouse Palates Cultured

The maxiHary regions of day−125 and day−1351CR mouse fetuses were cultivated 重n a cheIpically −defined serumless medium by a suspension culture technique to examine the toxic effects of 5−fluorouraci1 (5−FU )and hydroxyurea(HU )on cultured palates and to compare the sensitivity of fetal mouse palates at different s ages of develop− ment . The palates of day−12.5 and day−135 fetal mice were explanted and exposed in vitro fbr 72 hr to O.レ 50 μg 5FUlml or to 5−76 μg HU /mL 5−FU inhibited the growth and fusion of day−125 palatal shelves in vitro dependently on its concentrations . Day −135 palates were significantly less sensitive to 5−FU than day−125 palates , and the minimal toxic concentrations (MTCs )of 5−FU were O.1 and 10 μglm】for day12.5 and day−135 fetal palates , respec 口vely . HU inhibited the in vitro growth and fusion of day−12.5 fetal palatal shelves in a concentration dependent manner , but only slightly suppressed the growth of day−13,5 fetal palates . The MTCs of HU were 19 and 76 μglml fbr day−125 and day−135 fetal palates , respectively . Therefbre , day−125 fetal mouse palates(atstage − 10r earlier stages of palatogenesis)seemed significantly more susceptible to these terato− genic 【han day−13.5 fetal palates(at stages 2−30f pa韮atogenes 重s). The palates of day−12.51CR fetal mice may be more suitable than day−13,5 palates f()r in vitro terato− gen and f{)r the study of mechanisms of normal and abnormal pal飢ogenesis ,