Induction of corticosteroid biosynthetic pathway by ACTH and high-density lipoprotein in newborn rat adrenocortical cells cultured in serum-free medium

Abstract

In order to investigate the role of rat high-density lipoprotein (HDL) on adrenal cholesterol accumulation and steroidogenic pathways (corticosteroid, i.e., 21-hydroxysteroid biosynthesis and reductive metabolism of progesterone), newborn rat adrenal cells cultured in serum-free medium were used. Incubation of [4- 14C]cholesterol-HDL (i) in serum-free medium compared to those in medium with lipoprotein-deficient serum, (ii) in serum-free medium with ACTH compared to those without ACTH, both showed an increase of labelled cholesterol in cells and of labelled 21-hydroxysteroids excreted in medium. Substitution of serum-supplemented medium by serum-free and cholesterol-free medium led to a deep decrease of ACTH-induced steroid biosynthesis with a predominance of 20α-reduced steroids; addition of HDL restored the corticosteroid biosynthesis and decreased the reductive metabolism. Addition of increased concentrations of HDL (7–150 μg cholesterol/ml) enhanced, in a saturable fashion, the total cholesterol uptake and the corticosteroid biosynthesis. The total cholesterol accumulation in cells exceeded by 4-fold the steroid production at saturation. The ratio between the two steroidogenic pathways increased up to 40 at saturation in favor of corticosteroids. These results suggest that HDL is at least partly internalized and that probably its constituents contribute greatly to the control of the two different steroidogenic pathways.