Hydroxylated sterols : matabolism and effects on steroid production and steroid uptake

The isolated rat adrenal cell was used as a model system. The isolation technique for rat adrenal cells has been extensively studied : in our laboratory (Falke et al., 1975a,b, 1976a,b) . Starting with these cells we looked at the properties of hydroxylated sterols as a precursor for steroid production. In :intact cells exogenous substrates have to pass through several membranes to reach the mitochondrion, where the side-chain cleavage occurs. In order to eliminate possible effects on transport through membranes, we also used damaged bovine adrenal mitochondria to investigate the conversion of hydroxylated sterols. We also studied the effects of hydroxylated sterols on short-term stimuli of steroid production. Either the total cell suspension (Chapters 4 and 5) or suspensions containing largely glomerulosa cells or fasciculata/reticularis cells (Chapter 6) were used in these studies. Before exerting their action, steroid hormones have to be taken up by target cells and bound to receptors. It is commonly assumed that steroid hormones diffuse passively through the cell membrane, although there is some evidence for a mediated uptake rnechanism (Rao, 1981). In the rat, corticosterone is the main glucocorticoid and the liver is an important target organ. To study possible effects of hydroxylated sterols on steroid uptake we used the uptake of corticosterone in isolated rat liver cells as a model system (Chapter 7). In addition the effects of several sterols on the uptake and conversion of pregnenolone in isolated rat adrenal cells were investigated (Chapter 8) . As will be discussed in Cllapter 3, the method of cell isolation used for the rat adrenal can be applied to the human fetal adrenal, yielding viable cells. Also the method of separating cells of the fetal zone from those of the definitive zone by means of density gradient centrifugation can be used. With these cells the properties of hydroxylated sterols as steroid precursors were studied ( Chapter 9) .