Estranes are a type of steroid hormone related to estrogen, which is a female sex hormone. Estranes are not normally produced in the human body but can be found in some plants and animals. They are often used in hormone replacement therapy and contraceptives. Examples of estranes include equilin and equilenin, which are found in the urine of pregnant mares.

It's important to note that while estranes have estrogen-like effects on the body, they may also have unique properties and potential side effects compared to traditional estrogens. Therefore, their use should be carefully monitored and managed by a healthcare professional.