to adrenocortical cells under high steroidogenic pressure conditions, like stress. More specifi cally, probucol-induced lowering of both HDL-cholesterol and LDL-cholesterol levels in mice is associated with a >55% decrease in the glucocorticoid response to endotoxemia ( 1 ). Studies in LCAT and APOA1 knockout mice, respectively, have indicated that a specifi c decrease in plasma HDL-cholesterol levels is associated with a 25-50% decrease in the maximal adrenal glucocorticoid output ( 2, 3 ). Moreover, disruption of (adrenal-specifi c) HDL receptor function in mice is associated with a 40-50% decrease in the adrenocortical steroidogenic capacity ( 4, 5 ).Male carriers of functional mutations in the HDL biogenesis genes, ABCA1 and LCAT, display a decrease in the 24 h urinary excretion rate of adrenal-derived steroids ( 6 ). However, basal and stimulated plasma cortisol levels are similar in HDL-defi cient male ABCA1 and LCAT mutation carriers and their normolipidemic controls ( 6 ). Furthermore, both the urinary glucocorticoid excretion rate and cortisol response to corticotropin are unaltered in females with genetically low HDL ( 7 ). The presence of relatively low HDL-cholesterol levels is, thus, in striking contrast to what is observed in mice: not consistently associated with glucocorticoid insuffi ciency in humans.In vitro studies have suggested that both HDL and APOB-containing lipoproteins, i.e., VLDL and LDL, can theoretically supply cholesterol to adrenocortical cells ( 8-11 ). Importantly, human subjects exhibit a markedly different lipoprotein profi le as compared with mice. The majority of cholesterol in humans is carried by LDL, while the murine lipoprotein profi le is characterized by relatively low to absent levels of cholesterol associated with VLDL/LDL in the context of normal HDL-cholesterol levels. The relative importance of HDL-associated cholesterol as steroidogenic substrate can, thus, hypothetically be different between these two specifi c species due to the fact that human plasma, as compared with murine plasma, contains additional potential cholesterol sources, i.e., LDL Abstract The contribution of HDL to adrenal steroidogenesis appears to be different between mice and humans. In the current study, we tested the hypothesis that a difference in lipoprotein profi le may be the underlying cause. Hereto, we determined the impact of HDL defi ciency on the adrenal glucocorticoid output in genetically modifi ed mice with a human-like lipoprotein profi le. Genetic deletion of APOA1 in LDL receptor (LDLR) knockout mice was associated with HDL defi ciency and a parallel increase in the level of cholesterol associated with nonHDL fractions . Despite a compensatory increase in the adrenal relative mRNA expression levels of the cholesterol synthesis gene, HMG-CoA reductase, adrenals from APOA1/LDLR double knockout mice were severely depleted of neutral lipids, as compared with those of control LDLR knockout mice. However, basal corticosterone levels and the adrenal glucocorticoid response to stress we...