Verbal memory scores are frequently used as one measure of higher level cognition . These scores vary in direct proportion to estrogen levels throughout the menstrual cycle, pregnancy, and menopause. Furthermore, estrogens when administered shortly after natural or surgical menopause prevents decreases in verbal memory. In contrast, estrogens have little effect on verbal memory if first administered years after menopause.  Estrogens also have positive influences on other measures of cognitive function.  However the effect of estrogens on cognition is not uniformly favorable and is dependent on the timing of the dose and the type of cognitive skill being measured. 
The conversion of HMG-CoA to mevalonate by HMG-CoA reductase is the rate-limiting step of cholesterol biosynthesis and is under strict regulatory control (see Figure 1 ). HMGR is the target of compounds that are effective in lowering serum cholesterol levels. Human HMG-CoA reductase consists of a single polypeptide chain of 888 amino acids. The amino-terminal residues are membrane bound and reside in the endoplasmic reticulum membrane, while the catalytic site of the protein resides in its cytoplasmic, soluble carboxy-terminal portion. A linker region connects the two portions of the protein.