Role of albumin for the cholesterol transport and on the steroidogenic pathways in serum-free medium newborn rat adrenocortical cell cultures.

[3,4-13C]cholesterol-albumin complex incubated in serum-free medium allowed to evaluate quantitatively the transfer of cholesterol in newborn rat adrenocortical cultured cells, its accumulation as free cholesterol or cholesterol esters and its transformation into steroids which were also originated (47%) from intracellular unlabelled cholesterol. Increasing concentrations of albumin up to 5 g/l enhanced the production of total steroids but in the meantime decreased the 21-hydroxylated steroid fraction. Internalization of albumin shown by using [methyl-14C]methylated-albumin as a tracer accounted only for a minor part in the cholesterol uptake but strikingly affected the steroidogenic pathways by favoring the reductive metabolism of progesterone over the corticosteroid biosynthesis.