ESTRONE is considered a minor female sex hormone – one of the three main female sex steroid hormones, and similar to ESTRIOL has weak estrogenic activity compared to ESTRADIOL .

• Predominant estrogen produced by menopausal women.  ESTRONE serves mainly as a precursor to ESTRADIOL. Aging ovaries produce less ESTRADIOL, and ESTRONE concentration increases to make up for that decrease.
• High levels seen in first trimester of pregnancy
• Synthesized from cholesterol – via enzymes and pathways as shown in above schematic;
• Produced /secreted mainly from ovaries and testicles, but can also be formed in the adrenal glands and adipose tissue;