Marcinkiewicz J L, Bahr J M
Department of Animal Sciences, University of Illinois, Urbana 61801.
Biol Reprod. 1993 Feb;48(2):403-8. doi: 10.1095/biolreprod48.2.403.
The corpus luteum of the rabbit requires estradiol (E2) and the conceptus to maintain progesterone (P4) during the second half of pregnancy. The factor produced by the fetal placenta that is responsible for maintaining P4 production has not yet been identified. Therefore, the goal of these experiments was to determine whether the rabbit placenta contained luteotropic activity and to begin preliminary characterization of this factor. A bioassay system utilizing corpora lutea explants incubated with placental extracts and other treatments was developed and validated. Neither pooled placental extracts (200 micrograms) nor E2 alone affected P4 production (p > 0.05). However, the combination of placental extracts plus E2 significantly stimulated P4 production approximately 1.5-fold (p < 0.05). Skeletal muscle (200 micrograms) + E2 also had no effect on P4 production, indicating that the effect of placental extracts was tissue-specific. Carboxymethyl-cellulose ion-exchange chromatography of placental extracts yielded four separate fractions, which were examined individually at three doses for activity in the bioassay system. The first and most acidic fraction (Fraction 1) significantly stimulated P4 production at 10 and 100 micrograms when incubated in combination with E2 (p < 0.05). Both heat and trypsin treatment abolished the ability of placental Fraction 1 to stimulate P4 production in the presence of E2. Size fractionation of Fraction 1 using dialysis membranes with 3500, 6000-8000, and 12,000-14,000 molecular weight cutoff points had no effect on bioactivity of Fraction 1. These results indicate that the rabbit placenta contains a potential luteotropin with the characteristics of an acidic, heat-sensitive protein greater than 12,000-14,000 in molecular weight.
兔的黄体在妊娠后半期需要雌二醇（E2）和孕体来维持孕酮（P4）水平。胎儿胎盘产生的负责维持P4分泌的因子尚未被确定。因此，这些实验的目的是确定兔胎盘是否含有促黄体活性，并开始对该因子进行初步表征。开发并验证了一种生物测定系统，该系统利用与胎盘提取物及其他处理孵育的黄体外植体。无论是混合胎盘提取物（200微克）还是单独的E2都不影响P4的分泌（p>0.05）。然而，胎盘提取物与E2的组合显著刺激P4分泌，约为1.5倍（p<0.05）。骨骼肌（200微克）+E2对P4分泌也没有影响，表明胎盘提取物的作用具有组织特异性。胎盘提取物经羧甲基纤维素离子交换色谱法得到四个单独的组分，在生物测定系统中分别以三种剂量检测其活性。当与E2一起孵育时，第一个也是酸性最强的组分（组分1）在10微克和100微克时显著刺激P4分泌（p<0.05）。加热和胰蛋白酶处理都消除了胎盘组分1在E2存在下刺激P4分泌的能力。使用截留分子量为3500、6000 - 8000和12000 - 14000的透析膜对组分1进行大小分级分离，对组分1的生物活性没有影响。这些结果表明，兔胎盘含有一种潜在的促黄体素，其特征为一种分子量大于12000 - 14000的酸性、热敏感蛋白。
