Adrenal cholesterol uptake from plasma lipoproteins: regulation by corticotropin.

Abstract

The transfer of lipoprotein-bound cholesterol into adrenal cells was examined. Adrenal glands from unstimulated or ACTH stimulated hypophysectomized rats were incubated with high density lipoprotein (HDL) or low density lipoprotein [LDL] containing radiolabeled cholesterol. The rate of transfer of labeled cholesterol from HDL into the glands was 2-3 times greater than from LDL. ACTH stimulation increased the transfer of cholesterol from HDL but not LDL. The effects of ACTH were not dependent on subsequent cholesterol utilization for steroidogenesis. The process of cholesterol transfer from HDL was linear with time over 2 h at 37.degree. and greatly reduced at 4.degree.. The transfer process became saturated above an HDL cholesterol concentration of 900 .mu.g/ml. About 25% of the labeled adrenal cholesterol arising from HDL was recovered within the mitochondria. The labeled cholesterol within isolated mitochondria could undergo mitochondrial conversion to pregnenolone. The delipidated HDL apolipoproteins, apoA-I and apoA-II, when added to incubations containing less than saturating concentrations of HDL, stimulated transfer of labeled cholesterol from HDL to adrenal cells. Rat adrenal tissue probably possesses an HDL specific hormonally-responsive mechanism for accumulating extracellular cholesterol, and apoA-I and apoA-II probably have a significant function in the uptake process.