The role of serum high density lipoproteins in adrenal steroidogenesis

The rat adrenal cortex possesses at least two mechanisms for uptake of extracellular lipoprotein cholesterol; one is receptor mediated endocytosis and the second is a non-endocytotic pathway. The latter was revealed by the ability of lipoproteins such as HDL which do not possess apo B or apo E to enhance steroid hormone output. Rat adrenocortical cell uptake of HDL cholesterol is saturable and differs for unesterified cholesterol and cholesterol esters. In addition rat adrenocortical cells possess ACTH regulated HDL binding sites although the relationship of HDL receptor activity to cholesterol uptake remains uncertain. Further elucidation of the "HDL pathway" in the rat adrenal cortex may have biologic significance beyond understanding adrenal function since many non-steroidogenic tissues also possess HDL receptors and in man circulating levels of HDL-cholesterol are a strong inverse risk factor for accelerated atherosclerosis.