Pharmacodynamics E1S itself is essentially biologically inactive, with less than 1% of the relative binding affinity of estradiol for the<unk> n receptors (ERs), ERα and ERβ. The compound acts as a prodrug of<unk>  and more importantly of estradiol, the latter of which is a potent agonist of the ERs. Hence, E1S is an<unk> n. Pharmacokinetics E1S is cleaved by steroid<unk> se (also called<unk> n<unk> se) into<unk> . Simultaneously,<unk> n sulfotransferases transform<unk>  back into E1S, which results in an equilibrium between the two steroids in various tissues. E1S is thought to serve both as a rapidly-acting prodrug of estradiol and also as a long-lasting reservoir of estradiol in the body, which serves to greatly extend the duration of estradiol when used as a medication. When estradiol is administered orally, it is subject to extensive first-pass metabolism (95%) in the intestines and liver. A single administered dose of estradiol is absorbed 15% as<unk> , 25% as E1S, 25% as estradiol glucuronide, and 25% as<unk>  glucuronide. Formation of<unk> n glucuronide conjugates is particularly important with oral estradiol as the percentage of<unk> n glucuronide conjugates in circulation is much higher with oral ingestion than with parenteral estradiol.<unk>  glucuronide can be reconverted back into estradiol, and a large circulating pool of<unk> n glucuronide and<unk>  conjugates serves as a long-lasting reservoir of estradiol that effectively extends its terminal half-life of oral estradiol. To demonstrate the importance of first-pass metabolism and the<unk> n conjugate reservoir in the pharmacokinetics of estradiol, the terminal half-life of oral estradiol is 13 to 20 hours whereas with intravenous injection its terminal half-life is only about 1 to 2 hours.<unk> n<unk> s like<unk> are about twice as potent as the corresponding free<unk> ns in terms of<unk> nic effect when given orally to rodents. This in part led to the introduction of conjugated<unk> ns (Premarin), which are primarily<unk>  in 1941.
Estrone sulfate 
Estradiol undecylate
Estradiol dienantate
Estradiol furoate
Estradiol enantate
Androstenediol dipropionate
Estradiol dipropionate
Estradiol hemisuccinate