Oestrone hormone. Molecular model of the structure of the female sex hormone oestrone. Atoms are represented as balls and are colour-coded: carbon (blue), hydrogen (gold), and oxygen (red). Oestrone is one of three naturally-occurring oestrogens, a class of hormones that are associated with the development of the female reproductive organs and secondary sex characteristics. Oestrone is secreted in the ovaries and maintains female fertility up until the menopause. Oestrone sulphate may be used in hormone replacement therapy to treat some clinical symptoms of the menopause.