The pharmacology of oestriol.

The potency ratio of oestriol compared to oestradiol or to ethinyloestradiol depends on the experimental conditions of the test. If a sufficiently high level of oestriol is maintained in a target tissue, either by infusion or by frequent administration, this steroid is capable of eliciting a full oestrogenic effect. At the target tissue, oestriol is a short-acting rather than a weak-acting oestrogen. This explains why certain oestrogenic effects are not observed after a single administration of oestriol or after far-spaced dosings. The short retention time of oestriol in the target tissues makes the oestrogenic effects dependent on the manner of administration of the compound, in particular on the route of administration and on the frequency of dosing.