Menstruation Research Today is a free monthly online journal that collates and summarizes the latest research about Menstruation, including details on menstrual cycle, pregnancy, pain, irregular menstruation.

Meiosis-activating sterol synthesis in rat preovulatory follicle: is it involved in resumption of meiosis?

Cao X, Pomerantz SH, Popliker M, Tsafriri A

Bernhard Zondek Hormone Research Laboratory, Department of Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel.

Meiosis-activating sterol (MAS) was shown to overcome the inhibitory effect of hypoxanthine on spontaneous maturation of mouse oocytes and was suggested to mediate the stimulation of meiosis by gonadotropins. Follicular fluid (FF)-MAS is synthesized by cytochrome P450 lanosterol 14alpha-demethylase (LDM). Follicular LDM was preferentially localized in oocytes by immunohistochemistry. Using [3H]acetate or R-[5-3H]mevalonate as precursors as well as high-performance liquid chromatographic and thin-layer chromatographic separation, we have measured the concentrations of de novo-synthesized lanosterol, FF-MAS, and cholesterol in rat graafian follicles, cumulus-oocyte complexes (COCs), and denuded oocytes (DOs) treated with LH, AY-9944 (an inhibitor of Delta14-reductase, which was anticipated to increase FF-MAS levels by inhibiting its metabolism), or both after 8 h of culture. In follicles, both LH and AY-9944 increased the accumulation of FF-MAS as compared to controls. In COCs, AY-9944 caused a marked increase in FF-MAS, but we were unable to detect accumulation of FF-MAS in DOs. Neither the endogenous increases in FF-MAS accumulation nor the addition of FF-MAS to the culture medium could overcome the inhibition on resumption of meiosis by phosphodiesterase inhibitors. Compared to LH-induced resumption of meiosis in follicles, that induced by AY-9944 was much delayed. These results call into question any role of FF-MAS as an obligatory mediator of LH activity on germinal vesicle breakdown. The discrepancy between the positive staining for LDM in oocytes and our inability to detect de novo synthesized FF-MAS in DOs may relate to the sensitivity of the methodology employed and either the number of oocytes used or a deficiency in LDM synthetic activity in such oocytes. Further studies are required to confirm any of these alternatives.

Published 23 November 2004 in Biol Reprod, 71(6): 1807-12.
Full-text of this article is available online (may require subscription).

© 2004-2008 Menstruation Research Today. All Rights Reserved.