HMG CoA reductase is a rate controlling enzyme in the pathway that synthesizes cholesterol within the cell. Usually this enzyme is suppressed when the process of LDL (low-denity lipoprotein) internalization is taking place, this is because LDL is a cholesterol transport molecule, and it is presumed that if the cell is internalizing cholesterol from outside, it does not need to synthesize it's own through the pathway with HMG CoA reductase. So it's been proposed that there is definetly some kind of coordination between these two pathways and even though the full expanse of it is not yet known, we've still be able to utilize it. Competative inhibition of this reductase enzyme leads to expression of LDL receptors, and thus lower concentration of cholesterol outside the cell because it is being properly internalized and metabolized. Furthermore, in regards to patients with high cholesterol, they can be given "cholesterol-lowering" drugs like statins to help, which target the HMG reductase enzyme in this way.