Estrone, also known as E1 or osterone, is a C-18 steroid hormone. Estrone is one of the three naturally occurring estrogens, the others being estradiol and estriol. Estrone is produced primarily from androstenedione originating from the gonads or the adrenal cortex and from estradiol by 17-hydroxysteroid dehydrogenase. Androstenedione is also converted into estrone by aromatase (CYP19) and is expressed in stromal and carcinoma or parenchymal components of breast cancer tissue. Estrone is identical across all species and so this kit should measure estrone from all sources.
The estrogens are involved in the development of female sex organs and secondary sex characteristics. Before the ovum is fertilized the main action of the estrogens is on the growth and function of the reproductive tract in order to prepare it for the fertilized ovum. During the follicular phase of the menstrual cycle the estrone level shows a slight increase. The production of estrone then increases markedly to peak at around day 13. The peak is of short duration and by day 16 of the cycle levels will be low. A second peak occurs at around day 21 of the cycle and if fertilization doesnot occur, then the production of estrone decrease.