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 reducing the telogen phase and E2 treatment reversing this effect. E2 was found to be up to 100 times more potent than androgens in this context. 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.