Larrea F, Moctezuma O, Pérez-Palacios G
J Steroid Biochem. 1984 Apr;20(4A):841-7. doi: 10.1016/0022-4731(84)90393-5.
The acute and chronic effects of norethisterone (NET) upon gonadotropin dynamics were studied in long-term ovariectomized adult Wistar rats. Time course studies showed that plasma LH declined within 1 h following a single NET sc injection and remained low for the next 4 h duration of the experiment. Pre-treatment with tamoxifen prevented the acute anti-gonadotropic effect of NET and GnRH administration to NET treated rats resulted in an abolishment of the pituitary responsiveness in terms of LH. Chronic administration of NET but not progesterone to castrated animals induced a significant decrease of plasma and pituitary LH with a concomitant replenishment of hypothalamic GnRH in an identical fashion to that observed with chronic administration of 17 beta-estradiol. Furthermore, administration of NET and 17 beta-estradiol but not progesterone diminished the number of GnRH pituitary binding sites to levels found prior castration. These results indicate that the effects of this 19-nor synthetic progestin upon gonadotropin modulation in the long-term gonadectomized rat do not resemble those of progesterone and suggest that NET is acting through different mechanisms. The data are consistent with an estrogen-like mode of action.
在长期卵巢切除的成年Wistar大鼠中研究了炔诺酮（NET）对促性腺激素动态的急性和慢性影响。时间进程研究表明，单次皮下注射NET后1小时内血浆促黄体生成素（LH）下降，并在实验的接下来4小时内保持低水平。用他莫昔芬预处理可预防NET的急性抗促性腺激素作用，对NET处理的大鼠给予促性腺激素释放激素（GnRH）会导致垂体在LH方面的反应性消失。对去势动物长期给予NET而非孕酮会导致血浆和垂体LH显著降低，同时下丘脑GnRH以与长期给予17β-雌二醇相同的方式得到补充。此外，给予NET和17β-雌二醇而非孕酮会使GnRH垂体结合位点数量减少至去势前的水平。这些结果表明，这种19-去甲合成孕激素对长期去势大鼠促性腺激素调节的作用与孕酮不同，并提示NET通过不同机制起作用。数据与类似雌激素的作用模式一致。
