Metabolism of high density lipoprotein by human fetal adrenal tissue

The role of lipoproteins as a source of the cholesterol utilized for steroidogenesis by human fetal adrenal (HFA) tissue was investigated previously. It was found that low density lipoprotein (LDL) was the lipoprotein preferred as a source of cholesterol for steroidogenesis by the HFA. [l25I]Iodo- LDL was taken up and degraded by HFA tissue in organ culture, and the degradation of [^l25I]iodo-LDL was stimulated when ACTH (1 μg × ml⁻¹) was present in the culture medium. Others have shown that high density lipoprotein (HDL) is utilized as a source of cholesterol for steroidogenesis by rat adrenocortical cells in vitro and by the adrenals of the adult rat in vivo. In the present investigation we evaluated the metabolism of [¹²⁵I]iodo-HDL by HFA tissue. [¹²⁵I]Iodo-HDL uptake by the HFA tissue increased in a linear manner with time and as the concentration of [¹²⁵I]iodo-HDL in the culture medium was increased. However, there was little degradation of [^l25I]iodo- HDL by HFA. Moreover, preincubation of HFA tissue in medium containing ACTH (1 μg × ml⁻¹) or HDL, in various concentrations, did not affect the rate of uptake and degradation of [¹²⁵I]iodo-HDL. The rate of degradation of [¹²⁵I]iodo-LDL was found to decrease to low levels as the concentration of nonradiolabeled LDL in the culture medium was increased, whereas nonradiolabeled HDL had little effect on the degradation of [^l25I]iodo-LDL. HFA tissue fragments were incubated in medium containing ACTH plus lipoprotein-poor serum (LPPS) alone or LPPS plus HDL in various concentrations (50-1000 μg × ml⁻¹) The medium was changed daily and assayed for dehydroisoandrosterone sulfate and cortisol. In the presence of HDL, steroid secretion rates were no greater than those attained by HFA maintained in medium containing LPPS. It is concluded that the HFA utilizes cholesterol derived from LDL for steroidogenesis and that HDL is not metabolized efficiently by the human fetal adrenal.