Feedback regulation of HMG-CoA reductase activity

Fibroblasts obtained from a normal subject or from a patient homozygous for familial hypercholesterolemia (FH Homozygote) were grown in monolayer cultures.

a. At time zero, the medium was replaced with fresh medium depleted of lipoproteins, and HMG-CoA reductase activity was measured in extracts prepared at the indicated times.

b. Twenty-four hours after addition of the lipoprotein-deficient medium, human LDL was added to the cells at the indicated levels, and HMG-CoA reductase activity was measured at the indicated time.