Petrino T R, Lin Y W, Wallace R A
Whitney Laboratory, University of Florida, St. Augustine 32086.
Gen Comp Endocrinol. 1989 Jan;73(1):147-56. doi: 10.1016/0016-6480(89)90065-8.
In order to understand better the mechanism of gonadotropin action on steroidogenesis in prematurational follicles of Fundulus heteroclitus, follicle synthesis of 17 alpha-hydroxy, 20 beta-dihydroprogesterone (17 alpha-OH,20 beta-DHP), testosterone (T), and 17 beta-estradiol (E2) from a variety of precursors and the maturational response of oocytes were simultaneously followed in vitro. The addition of 25-hydroxycholesterol, pregnenolone, or progesterone to unstimulated follicles increased media 17 alpha-OH,20 beta-DHP, T, and E2, as well as oocyte germinal vesicle breakdown (GVBD) in a dose-dependent manner. Inhibition of cholesterol side-chain cleavage by aminoglutethimide blocked 25-hydroxycholesterol-promoted steroid accumulation and GVBD, indicating that 25-hydroxycholesterol does not directly induce GVBD, but rather is metabolized in the follicle to an active steroid (presumably 17 alpha-OH,20 beta-DHP). Likewise, trilostane, an inhibitor of delta 5-3 beta-hydroxysteroid dehydrogenase, blocked pregnenolone action. Both inhibitors also completely abolished steroid accumulation and GVBD promoted by a F. heteroclitus pituitary extract (FPE), but not GVBD induced by exogenous 17 alpha-OH,20 beta-DHP. FPE also significantly depressed T but enhanced E2 production from exogenous precursors. We have concluded from these observations that (1) cholesterol side-chain cleavage and pregnenolone conversion to progesterone are essential for gonadotropin-promoted follicle steroid production and the resulting reinitiation of meiosis by the oocyte, (2) the enzymes necessary for the conversion of cholesterol to 17 alpha-OH,20 beta-DHP, T, and E2 are present in the unstimulated, prematurational follicle, and (3) gonadotropin initiates steroidogenesis by acting at a step prior to the conversion of cholesterol to pregnenolone; it also appears to enhance aromatase activity.
为了更好地理解促性腺激素对底鳉早熟卵泡中类固醇生成的作用机制，体外同时追踪了卵泡从多种前体物质合成17α-羟基、20β-二氢孕酮（17α-OH，20β-DHP）、睾酮（T）和17β-雌二醇（E2）的过程以及卵母细胞的成熟反应。向未受刺激的卵泡中添加25-羟胆固醇、孕烯醇酮或孕酮，会以剂量依赖的方式增加培养基中17α-OH，20β-DHP、T和E2的含量，以及卵母细胞生发泡破裂（GVBD）的发生率。氨鲁米特抑制胆固醇侧链裂解可阻断25-羟胆固醇促进的类固醇积累和GVBD，这表明25-羟胆固醇不会直接诱导GVBD，而是在卵泡中代谢为一种活性类固醇（可能是17α-OH，20β-DHP）。同样，δ5-3β-羟基类固醇脱氢酶抑制剂曲洛司坦可阻断孕烯醇酮的作用。这两种抑制剂还完全消除了底鳉垂体提取物（FPE）促进的类固醇积累和GVBD，但并未消除外源性17α-OH，20β-DHP诱导的GVBD。FPE还显著降低了外源性前体物质产生的T，但增加了E2的产生。从这些观察结果中我们得出结论：（1）胆固醇侧链裂解和孕烯醇酮转化为孕酮对于促性腺激素促进卵泡类固醇生成以及由此导致的卵母细胞减数分裂重新启动至关重要；（2）未受刺激的早熟卵泡中存在将胆固醇转化为17α-OH，20β-DHP、T和E2所需的酶；（3）促性腺激素通过作用于胆固醇转化为孕烯醇酮之前的步骤来启动类固醇生成；它似乎还增强了芳香化酶的活性。
