Tibolone: what does tissue specific activity mean?

Preclinical studies has found that tibolone can display a weak estrogenic, progestational and androgenic activity. The effect produced depends mainly on the target tissue involved. Clinical data indicate that tibolone produces the hormonal effects needed to treat climacteric symptoms and to prevent long-term effects of the menopause without stimulating breast and endometrial tissues. This clinical profile would be produced by the tissue specific activity of tibolone and its main metabolites. Tibolone's tissue specific activity may be explained by the interplay of several mechanisms, such as the metabolic conversion of tibolone to compounds with different biological activity, the classical interaction with the steroid receptor and the specific local metabolism, within the target tissue. Therefore, the tissue response and thus the clinical effect produced by tibolone in a given tissue seem to depend on the predominating mechanisms and interactions present in that tissue.