Lipoprotein receptors and steroidogenesis in adrenocortical cells

Steroid-producing tissues require a continuous supply of cholesterol for hormone synthesis. In the majority of the steroidogenic tissues the cholesterol is imported via the receptor-mediated uptake of lipoproteins, and therefore the influence on the lipoprotein receptors provides an additional level for the regulation of hormone synthesis. Hormones regulating the adrenocortical activity exert both short- and long-term action, and thus they may control the interactions of the major cholesterol delivery particles--low- (LDLs) and high-density lipoproteins (HDLs)--and their receptors in short- and long-term action, possibly modulating the signal transduction in the former case and the number and distribution in the latter. The LDL and HDL pathway and the signal transduction mechanism is briefly reviewed. Data are discussed concerning short- and long-term action of hormones (alpha-MSH and ACTH, respectively) on the HDL3 receptors of isolated adrenocortical cells. Short-term treatment with alpha-MSH and long-term treatment with ACTH increased the binding of HDL3 to zona glomerulosa and fasciculata cells, respectively, while both treatments increased the hormone production in the presence of HDL. The lipoprotein receptors were frequently found on the microvilli of adrenocortical cell membranes.