エトレチナートによる催奇形実験 ラットの全はい培養法を用いて

Abstract

Whole rat embryos with visceral yolk sac on days 9.5 and 10.5 of gestation were explanted and cultured for 36 and 24 hours respectively, in rat serum containing 0, 10, and 20μg/ml etretinate (ETR) dissolved in 0.125% dimethyl sulfoxide. The effects of ETR on the development and morphogenesis of embryos were examined by light and electron microscopy.When embryos were cultured in the medium containing 20μg/ml ETR, various abnormalities were observed: The diameter of visceral yolk sac, crown-rump length, head length, and number of somites were significantly decreased, and incidences of embryos failing to close the neural tube and turn the body axis, as well as, hypoplasia of maxillary and mandibular swellings were increased, compared with control or low ETR-containing (10μg/ml) cultures. Microscopically, embryos treated with 20μg/ml ETR, showed a decreased number of neuroepithelial and interstitial cells. Occasionally, there were cells exhibiting some degenerative changes including electron dense nuclei and cytoplasm, dispersed chromatin, dark mitochondria with dilated cristae, and large phagosomes. These findings suggest that the failure to close the neural tube, as well as, hypoplasia of maxillary and mandibular swelling may be due to cytological disturbances including cell death induced by ETR.Besides these findings, vascular formation was extensively suppressed in the viceral yolk sac of the embryos cultured with 20μg/ml ETR. In addition, endodermal cells of the yolk sac contained an abundance of electron-lucent vacuoles, lipid dropletes, and dark mitochondria with dilated cristae. Considering that the visceral yolk sac of early embryos plays an important role in nutritional supply, the findings of the present study strongly suggest that ETRinduced dysfunctions of the visceral yolk sac can partly be causes for abnormal development of embryos.