Histological and Absorptional Changes of Skin with Development of Rat Fetuses

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Immature epidermis, dermis and subcutaneous tissues were histologically observed in the fetal skin of rats on day 17 of pregnancy. The tissues had become thicker in the fetal skin by day 19, and formed the basement membrane. The strata corneum and granulosum were found in the fetal skin on day 21. The distance between the cutaneous surface and the vascular system increased with fetal development. None of the fetal skin contained any subcutaneous adipose tissue or sebaceous glands as in the maternal ones. Absorption ratios of radioactivities in the rat fetuses were assayed at 20 min after injecting ¹⁴C-phenol and ¹⁴C-4-tert-butylphenol into the amniotic fluid. The absorption of both compounds decreased with fetal development. The absorption of ¹⁴C-phenol was greater than that of ¹⁴C-4-tert-butylphenol in the rat fetuses in three stages. These results suggest that the decrease in the absorption with fetal development depends on the increase in the distance between the cutaneous surface and the vascular system, and on the formation of the stratum corneum. The lower absorption of the ¹⁴C-4-tert-butylphenol having high hydrophobicity could be because the fetal skin was without subcutaneous adipose tissue and sebaceous glands.