17b-Estradiol Is Abundant in Skin and Regulates the Hair Follicle Cycle and Mirex Tumor Promotion

The study found that 17b-estradiol (E2) levels in mouse skin were significantly higher than in serum, suggesting that skin is a major site for extraglandular estrogen biosynthesis. E2 was shown to influence the hair follicle cycle by blocking the transition from telogen to anagen, with castration leading to a reduced telogen phase. E2 was found to be up to 100 times more potent than androgens in reversing castration effects on hair growth. Additionally, E2 played a crucial role in regulating mirex tumor promotion, with E2 implants restoring tumor promotion responses in castrated mice to levels seen in intact mice. This indicated that E2 was a key ovarian hormone affecting both hair growth and chemical carcinogenesis in the skin.