Oestrogen and the cardiovascular system: the good, the bad and the puzzling

The concept that oestrogen replacement therapy is cardioprotective has been challenged recently by the negative results of randomized clinical trials in coronary heart disease. These data have come at a time of rapid advances in our understanding of the cellular mechanisms of oestrogen. In particular, the cloning of the classical oestrogen receptor (ERalpha), the identification of a novel ER isoform (ERbeta), the availability of specific ERalpha and ERbeta knockout mice models, and the elucidation of receptor functions and signalling pathways linked to non-genomic actions of oestrogen are helping to unravel this complex biology. In this article, these advances will be discussed with particular emphasis on the regulation of nitric oxide synthesis by oestrogen. Furthermore, the puzzling issues that have emerged and the potential for development of novel and specific therapeutic approaches will be highlighted.