Additional Information

Estradiol (estradiol-17b -estradiol) is a natural estrogen with a molecular mass of 272.4 daltons.  Most circulating estradiol is strongly bound to sex hormone binding protein and loosely bound to albumin.  It is estimated that only 1%-5% of serum estradiol is free (unbound).  In non-pregnant women, estradiol is secreted by the ovary and the corpus luteum.  The adrenals and testes (in men) are also believed to secrete minute amounts of estradiol.  Estradiol levels are lowest at menses and into the early follicular phase and rise in the late follicular phase to a peak just prior to the hLH (human Luteinizing Hormone) surge, initiating ovulation.  As the hLH peaks, the levels of estradiol decrease before rising again in the luteal phase.  Endometrial growth is stimulated by estradiol and progesterone (secreted by the corpus luteum) in preparation for implantation of a fertilized egg.  If conception does not occur, the secretion of estradiol and progesterone by the corpus luteum decreases, initiating menses. Levels of estradiol are useful in monitoring ovulatory status.  Because estradiol levels reflect follicular maturation, the measurement of estradiol as cited in scientific literature has been used as a valuable tool in the assessment of sexual development in children, anovulation and/or amenorrhea, polycystic ovary syndrome and causes of infertility and menopause.  Abnormally high levels in males are indicative of feminizing syndromes such as gynecomastia.  Estradiol also effects areas other than reproductive tissues such as cardiovascular, immune, and central nervous systems. For this reason, estrogen has been investigated in the pathogenesis of cardiovascular disease, hormone dependent cancers and osteoporotic fracture.