The action of ovarian hormones in cardiovascular disease

The incidence of cardiovascular disease (CAD) differs between men and women, in part because of differences in risk factors and hormones. This sexual dimorphism means a lower incidence in atherosclerotic diseases in premenopausal women, which subsequently rises in postmenopausal women to eventually equal that of men. These observations point towards estrogen and progesterone playing a lifetime protective role against CAD in women. As exogenous estrogen and estrogen plus progesterone preparations produce significant reductions in low-density lipoprotein (LDL) cholesterol levels and significant increases in high-density lipoprotein (HDL) cholesterol, this should in theory lower the risk of CAD. However, results from oral contraceptive (OC) use and combined estrogen and progesterone hormone replacement therapy (HRT) have suggested that hormone replacement regimes do not provide cardiovascular protection. In fact, depending on the preparation and the presence or absence of genetic risk factors, an increased risk of cardiovascular diseases such as venous thrombosis, myocardial infarction (MI) and stroke have been observed. Interestingly, in the majority of studies the increase in risk was highest in the first year, after which an increase in risk was not observed, and in some studies a lower risk of CAD was evident after four or five years of exogenous hormone administration. While the debate continues about the merits of HRT, and several good reviews exist on the statistics of CAD in relation to exogenous hormones, we have decided to review the literature to piece together the physiological actions of estrogen and progesterone preparations on the individual mechanistic components leading to CAD; namely, the altered endothelium and the haemostatic balance between coagulation and fibrinolysis. We present possible mechanisms for how HRT and OCs protect against MI in the absence of cardiovascular risk factors but increase the incidence of MI in their presence. We also speculate on the roles played by hormones on the short- and long-term risks of cardiovascular disease.

Glucose transporters: expression, regulation and cancer

Mammalian cells depend on glucose as a major substrate for energy production. Glucose is transported into the cell via facilitative glucose transporters (GLUT) present in all cell types. Many GLUT isoforms have been described and their expression is cell-specific and subject to hormonal and environmental control. The kinetic properties and substrate specificities of the different isoforms are specifically suited to the energy requirements of the particular cell types. Due to the ubiquitousness of these transporters, their differential expression is involved in various disease states such as diabetes, ischemia and cancer. The majority of cancers and isolated cancer cell lines over-express the GLUT family members which are present in the respective tissue of origin under non-cancerous conditions. Moreover, due to the requirement of energy to feed uncontrolled proliferation, cancer cells often express GLUTs which under normal conditions would not be present in these tissues. This over-expression is predominantly associated with the likelihood of metastasis and hence poor patient prognosis. This article presents a review of the current literature on the regulation and expression of GLUT family members and has compiled clinical and research data on GLUT expression in human cancers and in isolated human cancer cell lines.