INVOLVEMENT OF HIGH-DENSITY-LIPOPROTEIN AS SUBSTRATE CHOLESTEROL FOR STEROIDOGENESIS BY BOVINE ADRENAL FASCICULO-RETICULARIS CELLS

Adrenocorticosteroids are known to be synthesized from cholesterol whi ch may arise from de novo synthesis or from the uptake of low-density lipoproteins (LDL) or high-density lipoproteins (HDL). LDL is reported to be a main substrate for corticosteroid synthesis by bovine adrenoc ortical cells, although the role of HDL, which is well known to be use d for steroid biosynthesis in rat adrenals, is still obscure. Therefor e, we examined the role of HDL in the regulation of corticoste roidoge nesis in bovine adrenals in order to clarify whether or not HDL was se lectively utilized for corticosteroid synthesis in vitro. The present data demonstrated that HDL and LDL increased cortisol production in a dose-dependent manner in bovine adrenocortical cells in vitro, and als o that HDL cholesterol increased cortisol production significantly hig her than LDL cholesterol did. Addition of adrenocorticotrophic hormone (ACTH) with HDL to the incubation media enhanced much higher cortisol production than that with LDL in short time incubation. The present d ata also demonstrated that uptake of I-125-HDL was significantly great er than that of (125)l-LDL. Thus, HDL rather than LDL is thought to be the preferred lipoprotein as a source of steroidogenic substrate chol esterol in bovine adrenal fasciculo-reticularis cells.