Condon T P, Dykshoorn-Bosch M A, Kelly M J
Department of Physiology, Oregon Health Sciences University, Portland 97201.
Biol Reprod. 1988 Feb;38(1):121-6. doi: 10.1095/biolreprod38.1.121.
Negative feedback of estrogen was investigated in ovariectomized female guinea pigs. Two weeks after ovariectomy, indwelling catheters were inserted into the jugular vein, and 3 days later, blood samples were taken every 10 min to determine the pattern of luteinizing hormone (LH) secretion. LH secretion in these guinea pigs was episodic, with a mean pulse period of 32 min. The mean pulse amplitude was 2.1 ng/ml, with mean plasma LH levels of 1.8 ng/ml. Twenty-five micrograms 17 beta-estradiol (E2), given i.v., caused a pronounced inhibition of pulsatile LH release. Twenty-five microliters of 100% ethanol (vehicle) had no effect on plasma LH values. In a second set of experiments, ovariectomized female guinea pigs were given two injections of luteinizing hormone-releasing hormone (LHRH) (1 microgram/kg BW, i.v.) separated by 30 min. Sharp rises in serum LH values were detected after each injection. A third injection of LHRH was administered after an injection of either 25 micrograms E2 or 25 microliters vehicle. In the presence of E2, the LH response was significantly (p less than 0.005) diminished, whereas the vehicle did not change the LH response to LHRH. These rapid effects of E2 on LH secretion and the pituitary responsiveness to LHRH infusion indicate that in the ovariectomized guinea pig E2 can directly block gonadotropin secretion. These findings are consistent with the hypothesis that negative feedback actions of E2 are directly on the membrane of the gonadotrope.
在去卵巢的雌性豚鼠中研究了雌激素的负反馈作用。去卵巢两周后，将留置导管插入颈静脉，3天后，每10分钟采集一次血样以确定促黄体生成素（LH）的分泌模式。这些豚鼠的LH分泌是间歇性的，平均脉冲周期为32分钟。平均脉冲幅度为2.1 ng/ml，平均血浆LH水平为1.8 ng/ml。静脉注射25微克17β-雌二醇（E2）可显著抑制LH的脉冲式释放。25微升100%乙醇（溶媒）对血浆LH值无影响。在第二组实验中，给去卵巢的雌性豚鼠静脉注射两次促黄体生成素释放激素（LHRH）（1微克/千克体重），间隔30分钟。每次注射后均检测到血清LH值急剧上升。在注射25微克E2或25微升溶媒后再注射第三次LHRH。在E2存在的情况下，LH反应显著减弱（p<0.005），而溶媒对LH对LHRH的反应无影响。E2对LH分泌和垂体对LHRH输注反应的这些快速作用表明，在去卵巢的豚鼠中，E2可直接阻断促性腺激素的分泌。这些发现与E2的负反馈作用直接作用于促性腺激素细胞的细胞膜这一假说一致。
