The evolution and distribution of hydroxysteroid dehydrogenase activity in human foetal skin throughout gestation.

Specimens of skin from human foetuses from 6--41 weeks gestation were incubated to demonstrate the presence of hydroxysteroid dehydrogenases (HSDs) by histochemical methods. When present HSDs were noted only within the acini of the sebaceous glands and in the secretory duct. Seventeen-beta-HSD activity was first demonstrated at 16 weeks gestation, co-incident with full function in the glands. Three-beta- and 16beta-HSD activity did not appear until 22--24 weeks. There were differences between the foetal pattern of distribution of the enzymes within gland acini and that already known in skin from subjects in extrauterine life. The time of changeover to the latter pattern has been established as 38 weeks gestation. No correlation was noted between HSD activity and the sex of the foetus or body site. It is concluded that foetal skin is involved in steroid metabolism, and possible physiological roles for this activity are discussed, with speculation over skin as an excretory route or detoxication centre for steroids and the role of steriod metabolic activity in the local stimulation and functional control of foetal sebaceous glands.