Inhibition of Cholesterol Biosynthesis in Ovine Ovarian Follicles in vitro by Human Chorionic Gonadotrophin

Abstract

Cholesterol biosynthesis from DL-[2-14 C]mevalonic acid ([l4C]MVA) was demonstrated in ovine ovarian foIlicles and isolated thecal tissues and granulosaI ceIls incubated in vitro. Thecal tissues more readily synthesized cholesterol than did granulosal ceIls when incubated separately, but in the intact follicle the newly synthesized cholesterol distributed evenly between the two tissue layers, indicating that the theca could act as a supplementary source of cholesterol for the granulosal ceIls.Human chorionic gonadotrophin (hCG) added to the incubation medium was found to inhibit cholesterol biosynthesis from P 4 C]MVA by intact foIlicles and isolated thecal tissues, but not granulosal ceIls. This hCG-induced inhibition was evident in whole foIlicles incubated for 12-48 h, but not at 3-6 h, and was demonstrated in thecal tissues incubated for 3 h. In all cases where inhibition of cholesterol biosynthesis was observed, 1 4C label accumulated in a product characterized by thin layer and vapour phase chromatography as lanosterol, implying that the hCG block lies between lanosterol and cholesterol. Treatment of foIlicles with hCG also reduced the amount of 14C label incorporated into the cholesteryl ester fraction. These changes were accompanied by a corresponding reduction in the tissue content of cholesteryl ester, but there were no changes in the specific activities to indicate that newly synthesized cholesteryl ester was used selectively as a substrate for progestin biosynthesis.

Gonadotropin-Induced Accumulation of 4,4-Dimethylsterols in Mouse Ovaries and Its Temporal Relation to Meiosis1

“…In contrast, Douglas et al [29] reported that FSH exerts an inhibitory action on cholesterol formation in intact follicles and isolated theca cells but, interestingly, not in granulosa cells. They also found that an unidentified sterol intermediate accumulates during this response [29]. Although the extent of cholesterol biosynthesis de novo by granulosa cells displays a reverse dependency on the availability of lipoproteins [30,31], hCG stimulates cholesterol biosynthesis de novo, to some extent, in rat lutein cells independent of cholesterol availability [24].…”

“…1) [26][27][28]. In contrast, Douglas et al [29] reported that FSH exerts an inhibitory action on cholesterol formation in intact follicles and isolated theca cells but, interestingly, not in granulosa cells. They also found that an unidentified sterol intermediate accumulates during this response [29].…”

Lipid and pigment changes during shoot initiation in cultured explants of Pinus radiata

“…Free sterols were extracted along with the other lipids and separated frotn other lipids by tic (above). Sterol bands were scraped from the tic plates and then, after adding progesterone (50 ^g) as intemal standard, the sterols were eluted from the silica gel with diethyl ether (3 X 1 ml) (Douglas et al 1978). The diethyl ether eluates were taken to complete dryness under a stream of N,; hexamethyldisilazane (50 (il) and tritnethylchlotosilane (50 (tl) were added and the mixture was heated for 60 min at 60°C.…”

Quantitation of meiosis activating sterols in human follicular fluid using HPLC and photodiode array detection

“…Most cholesterol utilized for this purpose is generally believed to be derived from lipoproteins (Christie et al, 1979;Gwynne andStrauss, 1982, Grummer andCarroll, 1988). However, cholesterol synthesis de novo has been reported in ovine (Douglas et al, 1978), porcine (Barañao and Hammond, 1986) and bovine (Spicer et al, 1996) granulosa cells, rat ovaries (Bai et al, 1973) or luteal cells (Christie et al, 1979;Azhar et al, 1985), and isolated rabbit follicles (Mills and Savard, 1972), and it appears that steroidogenesis can proceed to some extent by the de novo pathway alone (Schuler et al, 1981).…”