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In the normal menstrual cycle, estradiol levels measure typically <50 pg/mL at menstruation, rise with follicular development (peak: 200 pg/mL), drop briefly at ovulation, and rise again during the luteal phase for a second peak. At the end of the luteal phase, estradiol levels drop to their menstrual levels unless there is a pregnancy.
Estradiol is an estrogen, or an agonist of the nuclear estrogen receptors (ERs), the estrogen receptor alpha (ERα) and the estrogen receptor beta (ERβ). [1] [2] [6] In one study, the EC 50 Tooltip half-maximal effective concentration value of estradiol for the human ERα was 50 pM (0.05 nM) and for the human ERβ was 200 pM (0.2 nM).
During pregnancy, levels of estradiol increase to very high concentrations that are as much as 100-fold normal levels. [138] [139] [140] In late pregnancy, the body produces and secretes approximately 100 mg of estrogens, including estradiol, estrone, and estriol, per day. [138]
Levels of sex hormones and SHBG during pregnancy in women. [29] Levels of SHBG and estradiol during pregnancy in women. [30] For SHBG the lines are the mean and 95th percentile levels while the points are individual measurements. [30] For estradiol the line is the mean level. [30] The dashed parts of the lines are extrapolated. [30]
The four major naturally occurring estrogens in women are estrone (E1), estradiol (E2), estriol (E3), and estetrol (E4). Estradiol (E2) is the predominant estrogen during reproductive years both in terms of absolute serum levels as well as in terms of estrogenic activity.
Estriol is a much less potent estrogen than is estradiol, and is somewhat weak and atypical in its properties. [ 4 ] [ 42 ] [ 44 ] [ 19 ] Given by subcutaneous injection in mice, estradiol is about 10-fold more potent than estrone and about 100-fold more potent than estriol. [ 51 ]
The influence of 2 mg/day oral estradiol valerate on coagulation factors is less than that of 10 μg/day oral ethinylestradiol. [93] [26] [94] [95] [96] Oral ethinylestradiol at 10 μg/day has been found to have about 1.5- to 2.5-fold the impact of 2 mg/day oral estradiol valerate on HDL cholesterol and triglycerides.
A higher dosage of estradiol gel containing 1.5 mg estradiol per daily application has been found to produce mean estradiol levels of 40 to 100 pg/mL and estrone levels of 90 pg/mL, while 3 mg per day has been found to result in respective mean estradiol and estrone levels of 60 to 140 pg/mL and 45 to 155 pg/mL. [15]