INDEPENDENT BEHAVIOR OF RAT-LIVER LDL RECEPTOR AND HMGCOA REDUCTASE UNDER ESTROGEN-TREATMENT

The main molecules of hepatic cholesterol homeostasis are HMGCoA reduc tase, the key enzyme of the biosynthetic pathway, and LDL receptor, re sponsible for the uptake of plasma lipoproteins. Estrogens are reporte d to cause hypolipidemia in mammalians inducing hepatic LDL receptor. The effect of such hormones on HMGCoA reductase is very ambiguous. The mechanism and the time-dependence of the effects of these hormones on HMGCoA reductase and LDL receptor in rat liver have been investigated at mRNA and protein levels, at different times after estrogen adminis tration. Estrogens cause an early increase of LDLr, at both mRNA and p rotein level, and an increase of HMGCoA reductase, just at protein lev el, detectable only after 5 days. The independent behavior of LDLr and HMGCoA reductase under estrogen treatment suggests a not coordinate r egulation by these hormones. (C) 1996 Academic Press, Inc.