Ethynyl estradiol is a semisynthetic alkylated ESTRADIOL with a 17-alpha-ethinyl substitution. It has high estrogenic potency when administered orally, and is often used as the estrogenic component in ORAL CONTRACEPTIVES.

Ethinyl Estradiol increases respiratory chain activity in both cultured rat hepatocytesand HepG2 cells. Ethinyl estradiol is a strong promoter of hepatocarcinogenesis. [1] Ethinyl Estradiol enhances the transcript levels of nuclear genome- and mitochondrial genome-encoded genes and respiratory chain activity in female rat liver, and also inhibits transforming growth factor beta (TGFbeta)-induced apoptosis in cultured liver slices and hepatocytes from female rats. Ethinyl Estradiol increases the transcript levels of the mitochondrial genome-encoded genes cytochrome oxidase subunits I, II, and III in cultured female rathepatocytes. Ethinyl Estradiol significantly increases both the levels of glutathione (reduced [GSH] and oxidized [GSSG] forms) per mg protein in mitochondria and nuclei, while the percentage of total glutathione in the oxidized form is not affected. [2]

Ethinyl Estradiol (50 mg/kg/day) increases anogenital distance and reduces pup body weight at postnatal day 2, accelerates the age at vaginal opening, reduces F1 fertility and F2 litter sizes, and induces malformations of the external genitalia (5 mg/kg) in the female Long-Evans rat. [3] Ethinyl Estradiol increases the number of low density lipoprotein (LDL) receptors in livers of rats, thereby producing a profound fall in plasma cholesterol levels. Ethinyl Estradiol exerts the same effect in livers of male and female rabbits and that the increase in receptor number is correlated with a 6- to 8-fold increase in the levels of receptor mRNA. [4]