Local oestrogenic/androgenic balance in the cerebral vasculature

Reproductive effects of sex steroids are well-known; however it is increasingly apparent that these hormones have important actions on non-reproductive tissues such as the vasculature. The latter effects can be relevant throughout the lifespan, not just limited to reproductive years, and are not necessarily restricted to one gender or the other. Our work has established that cerebral blood vessels are a non-reproductive target tissue for sex steroids. We have found that oestrogen and androgens alter vascular tone, endothelial function, oxidative stress and inflammatory responses in cerebral vessels. Often the actions of oestrogen and androgens oppose each other. Moreover, it is clear that cerebral vessels are directly targeted by sex steroids, as they express specific receptors for these hormones. Interestingly, cerebral blood vessels also express enzymes that metabolize sex steroids. These findings suggest that local synthesis of 17ß-estradiol and dihydrotestosterone can occur within the vessel wall. One of the enzymes present, aromatase, converts testosterone to 17ß-estradiol, which would alter the local balance of androgenic and oestrogenic influences. Thus cerebral vessels are affected by circulating sex hormones as well as locally synthesized sex steroids. The presence of vascular endocrine effector mechanisms has important implications for male-female differences in cerebrovascular function and disease. Moreover, the cerebral circulation is a target for gonadal hormones as well as anabolic steroids and therapeutic drugs used to manipulate sex steroid actions. The long-term consequences of these influences are yet to be determined.