Ortmann O, Emons G, Knuppen R, Catt K J
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Endocrinology. 1988 Aug;123(2):962-8. doi: 10.1210/endo-123-2-962.
The effect of keoxifene (LY 156 758) on GnRH-stimulated LH release and its ability to antagonize estrogen actions were investigated in rat anterior pituitary cells. Estrogens exert either stimulatory or inhibitory effects on GnRH-induced LH secretion in rat pituitary cells depending on the incubation time with the steroid. When pituitary cells were treated for 24 h with 10(-9) M estradiol, the LH response to GnRH was clearly enhanced, and this effect was completely inhibited by 300 nM keoxifene. Short term treatment (4 h) of pituitary cells with 10(-9) M estradiol inhibits GnRH-stimulated LH release, and this effect was also blocked by keoxifene in a dose-dependent manner. In the absence of exogenous estrogen the treatment of pituitary cells for 4 h with increasing concentrations of keoxifene reduced the LH response to 10(-9) M GnRH only at very high concentrations (10(-5) M) of the antiestrogen. After treatment for 24 h, the inhibitory effect of keoxifene was evident at concentrations greater than or equal to 10(-8) M, with a reduction of GnRH-induced LH release by up to 60%. The effects of the antiestrogen were also analyzed in a dynamic culture system, in which pituitary cells grown on microcarrier beads were continuously perifused with medium and stimulated with GnRH in a pulsatile fashion. The LH response to a 2 min pulse of 10(-9) M GnRH was reduced in magnitude after 40 min of perifusion with 10(-9) M estradiol. When keoxifene (300 nM) was present at the same time, the LH response was identical to that observed in vehicle-treated cells. At the concentration of 300 nM, keoxifene per se did not change the responsiveness of the pituitary cells to the GnRH stimulus. These findings show that keoxifene is a potent antagonist of both positive and negative estrogen actions in the pituitary gonadotroph. In addition, after short term treatment with high concentrations or after long term treatment, keoxifene itself exerts an inhibitory effect on GnRH-induced LH secretion.
在大鼠垂体前叶细胞中研究了凯昔芬（LY 156 758）对促性腺激素释放激素（GnRH）刺激的促黄体生成素（LH）释放的影响及其拮抗雌激素作用的能力。雌激素对大鼠垂体细胞中GnRH诱导的LH分泌具有刺激或抑制作用，这取决于与甾体激素的孵育时间。当垂体细胞用10⁻⁹ M雌二醇处理24小时时，对GnRH的LH反应明显增强，而300 nM凯昔芬可完全抑制这种作用。垂体细胞用10⁻⁹ M雌二醇进行短期处理（4小时）会抑制GnRH刺激的LH释放，这种作用也会被凯昔芬以剂量依赖性方式阻断。在没有外源性雌激素的情况下，用浓度不断增加的凯昔芬处理垂体细胞4小时，仅在非常高的抗雌激素浓度（10⁻⁵ M）下才会降低对10⁻⁹ M GnRH的LH反应。处理24小时后，凯昔芬在浓度大于或等于10⁻⁸ M时具有明显的抑制作用，可使GnRH诱导的LH释放减少高达60%。还在动态培养系统中分析了抗雌激素的作用，在该系统中，生长在微载体珠上的垂体细胞用培养基连续灌流，并以脉冲方式用GnRH刺激。用10⁻⁹ M雌二醇灌流40分钟后，对10⁻⁹ M GnRH 2分钟脉冲的LH反应幅度降低。当同时存在300 nM凯昔芬时，LH反应与在载体处理细胞中观察到的相同。在300 nM浓度下，凯昔芬本身不会改变垂体细胞对GnRH刺激的反应性。这些发现表明，凯昔芬是垂体促性腺细胞中雌激素正负作用的有效拮抗剂。此外，在高浓度短期处理或长期处理后，凯昔芬本身对GnRH诱导的LH分泌具有抑制作用。
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