Abstract
The influence of high density lipoproteins (HDL) on luteinizing hormone-stimulated rat ovarian theca/interstitial cell steroidogenesis was studied. Without HDL the cells produced primarily androgens from progestin precursors. In the presence of rat or human HDL steroid output increased 3-5-fold, but the type of steroid produced was dependent on the source of the HDL. Human HDL nonselectively amplified luteinizing hormone-stimulated steroid production, whereas rat HDL promoted progestin production without a concomitant increase in androgen output. Comparisons of the activities of apoprotein E-rich HDL (e.g. HDL from intact mature rats) with apoprotein E-poor HDL (e.g. human HDL or rat HDL from hypophysectomized immature rats) suggested that apoprotein E was responsible for the inhibition of androgen production. Furthermore, the inhibitory activity of rat HDL was abolished by depleting apoprotein E-containing lipoproteins with heparin affinity chromatography. Direct evidence that apoprotein E was the inhibitory constituent of rat HDL was obtained by showing that isolated lipid-free rat apoprotein E inhibited androgen production, whereas isolated rat apoproteins A-I and A-IV did not. The possible paracrine function of apoprotein E in ovarian follicular maturation of the ovary is discussed.
Highlights
High density lipoprotein (HDL) the cells produced primarily androgens from pro-of steroidogenesisby ovarian cells other than theca/interstigestin precursors.In the presenceof rat or human HDL tial cells
Because androgens are essential for follicular development and their synthesis is inhibited only in the presence of the homologous lipoprotein, further studies were performed to identify the active constituent of rat HDL (rHDL) responsible for the
Effectof human HDL (hHDL) and rHDL on Androgen Production-hHDL and rHDL were isolated from plasma by density gradient ultracentrifugation
Summary
Lipoprotein Isolation and Characterization-Fresh human plasma was obtained from normal fasting healthy male donors by plasmapheresis. Ouarian Cell Cultures-Hypophysectomized immature female rats (Sprague-Dawley; days old) were supplied by Johnson Laboratories (Bridgeview,IL). Analysis of the nonlabeled ovarian cell steroids was accomplished by radioimmunoassay as described below. Samples in which the separated steroids were to be measured by RIA had a recovery mixture added to them before extraction, which contained 25,000 cpm of [3H]pregnenolone,[3H]progesterone,[3H]20a-dihydroprogesterone, [3H]17a-hydroxyprogesterone,[3H]androstenedione, [3H]androsterone, [3H]androstanediol, and [3H]estradiol. Apoprotein Separation-Rat lipoproteins of d I1.019 g/ml and rHDL were delipidated with methyethyl ketone (MEK) (Sigma) [15]. For direct assay of the MEK-delipidated soluble proteins from rat lipoproteins of d I 1.019 g/ml, 1volume of the aqueous phase was treated with 2 volumes of acetone, and themixture vortexed. Heparin Affinity Chromatography-Both rat lipoproteins and apoproteins were separated into apoE-enriched and apoE-depleted fractions by heparin affinity chromatography [16]. Protein and cholesterol concentrations were measured as described above and thefractions analyzed by SDS-PAGE
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
