Adrenal function in heterozygous and homozygous hypobetalipoproteinemia

Corticosteroid synthesis in the human adrenal cortex requires a supply of cholesterol which can be derived from both local synthesis and the uptake of plasma lipoproteins. Studies with cultured adrenal cells have shown that such uptake is mediated through the interaction of plasma low density lipoproteins (LDL) and a specific cellular receptor (the LDL receptor). In the present study we have examined parameters of adrenal corticosteroid production in a patient with phenotypic abetalipoproteinemia (on the basis of homozygous hypobetalipoproteinemia) and in three of her relatives with inherently low levels of LDL (heterozygous hypobetalipoproteinemia). These studies sought to determine whether the absence of LDL or an inherent reduction in their plasma concentration results in alterations in corticosteroid production both under basal conditions and in response to prolonged stimulation with iv ACTH. Our results document normal parameters of corticosteroid production under basal conditions in both heterozygous and homozygous hypobetalipoproteinemia, but an impaired response to ACTH in the latter. This was manifested by significantly lower serum concentrations of cortisol as well as by reduced rates of excretion of 17OHCS, 17-ketosteroids, and urinary free cortisol during ACTH infusion. By inference, our results provide in vivo support for the view that plasma LDL serve as an important source of cholesterol for adrenal corticosteroid synthesis under conditions of sustained stimulation with ACTH.