Pharmacology
Pharmacodynamics
Estrogenic activity
DES is an estrogen; specifically, it is a highly potent full agonist of both of the estrogen receptors (ERs). It has approximately 468% and 295% of the affinity of estradiol at the ERα and ERβ, respectively. However, EC50 values of 0.18 nM and 0.06 nM of DES for the ERα and ERβ, respectively, have been reported, suggesting, in spite of its binding affinity for the two receptors, several-fold preference for activation of the ERβ over the ERα. In addition to the nuclear ERs, DES is an agonist of the G protein-coupled estrogen receptor (GPER), albeit with relatively low affinity (~1,000 nM). DES produces all of the same biological effects attributed to natural estrogens like estradiol. This includes effects in the uterus, vagina, mammary glands, pituitary gland, and other tissues.A dosage of 1 mg/day DES is approximately equivalent to a dosage of 50 µg/day ethinylestradiol in terms of systemic estrogenic potency. Similarly to ethinylestradiol, DES shows a marked and disproportionately strong effect on liver protein synthesis. Whereas its systemic estrogenic potency was about 3.8-fold of that of estropipate (piperazine estrone sulfate), which has similar potency to micronized estradiol, the hepatic estrogenic potency of DES was 28-fold that of estropipate (or about 7.5-fold stronger potency for a dosage with equivalent systemic estrogenic effect).DES has at least three mechanisms of action in the treatment of prostate cancer in men.
To discourage off-label use of DES as a postcoital contraceptive, the FDA in 1975 removed DES 25 mg tablets from the market and ordered the labeling of lower doses (5 mg and lower) of DES still approved for other indications changed to state: "This drug product should not be used as a postcoital contraceptive" in block capital letters on the first line of the physician prescribing information package insert and in a prominent and conspicuous location of the container and carton label. In the 1980s, off-label use of the Yuzpe regimen of certain regular combined oral contraceptive pills superseded off-label use of DES as a postcoital contraceptive.In 1978, the FDA removed postpartum lactation suppression to prevent breast engorgement from their approved indications for DES and other estrogens. In the 1990s, the only approved indications for DES were treatment of advanced prostate cancer and treatment of advanced breast cancer in postmenopausal women. The last remaining U.S. manufacturer of DES, Eli Lilly, stopped making and marketing it in 1997. Trials
Diethylstilbestrol has been used countless times in studies on rats. Once it was discovered that DES was causing vaginal cancer, experiments began on both male and female rats. Many of these male rats were injected with DES while other male rats were injected with olive oil, and they were considered the control group. Each group received the same dosage on the same days, and the researchers performed light microscopy, electron microscopy, and confocal laser microscopy.