Moll G W, Rosenfield R L
J Steroid Biochem. 1986 Sep;25(3):309-14. doi: 10.1016/0022-4731(86)90241-4.
We tested the influence of protein binding upon the rapid 17 beta-estradiol (E2) inhibitory effect on luteinizing hormone (LH) responsiveness to LH releasing hormone (LHRH) in perifused rat anterior pituitaries. LHRH pulses were given before 1 h after changing the perifusion medium to contain various combinations of protein and E2. In the absence of albumin an E2 concentration of about 27 pg/ml inhibited LH secretion in response to LHRH by 50% (judged from the change in secretion ratio, i.e LH response to LHRH pulse no. 2 divided by that to pulse no. 1). Albumin (1 g/dl) and human plasma enhanced the self-priming effect of LHRH (P less than 0.1) and blunted the slope of the dose-response relationship between E2 and LH secretion. These effects suggest a stimulatory effect of proteins on LH secretion which is independent of E2. However, proteins appear to antagonize the E2 effect in part by binding E2. A total E2 dose of 270 pg/ml or more was required to achieve about 50% inhibition of the LH secretion ratio in the presence of albumin. Since 20% of E2 was unbound in the presence of albumin, the 50% effective dose of free E2 was about 54 pg/ml. This closely approximates the comparably effective dose of E2 in the absence of protein. Although a total E2 concentration of 216 pg/ml was required for a 50%-inhibitory E2 effect in the presence of heat-inactivated plasma, this was equivalent to between 28 and 37 pg/ml of free E2 in these experiments. The effect of E2 in a total dose of 216 pg/ml was attenuated more by the use of TEBG-positive plasma than of TEBG-negative (heat-inactivated) plasma (P less than 0.01). Our data indicate that the E2 inhibitory effect upon LH responsiveness to LHRH is attenuated by albumin and TEBG to approximately the extent expected by binding of E2 to these proteins. Our data are certainly contrary to those expected if either albumin or TEBG augmented this E2 action. Our data support the concept that the bioavailable fraction of plasma sex steroids is that which is free from binding to plasma proteins.
我们测试了蛋白质结合对灌流大鼠垂体前叶中17β - 雌二醇（E2）对促黄体生成素（LH）对促性腺激素释放激素（LHRH）反应的快速抑制作用的影响。在将灌流培养基更换为含有蛋白质和E2的各种组合后1小时内给予LHRH脉冲。在没有白蛋白的情况下，约27 pg/ml的E2浓度可使LH对LHRH的分泌反应抑制50%（根据分泌率的变化判断，即LH对第2个LHRH脉冲的反应除以对第1个脉冲的反应）。白蛋白（1 g/dl）和人血浆增强了LHRH的自我启动作用（P < 0.1），并使E2与LH分泌之间的剂量反应关系斜率变钝。这些效应表明蛋白质对LH分泌有刺激作用，且该作用独立于E2。然而，蛋白质似乎部分通过结合E2来拮抗E2的作用。在有白蛋白存在的情况下，需要270 pg/ml或更高的总E2剂量才能使LH分泌率抑制约50%。由于在有白蛋白存在时20%的E2未结合，游离E2的50%有效剂量约为54 pg/ml。这与在没有蛋白质时E2的相当有效剂量非常接近。尽管在有热灭活血浆存在时，需要216 pg/ml的总E2浓度才能产生50%的E2抑制作用，但在这些实验中这相当于28至37 pg/ml的游离E2。与使用TEBG阴性（热灭活）血浆相比，使用TEBG阳性血浆时，216 pg/ml总剂量的E2的作用减弱更明显（P < 0.01）。我们的数据表明，E2对LH对LHRH反应的抑制作用被白蛋白和TEBG减弱的程度大致与E2与这些蛋白质结合所预期的程度相同。我们的数据肯定与如果白蛋白或TEBG增强这种E2作用所预期的数据相反。我们的数据支持这样的概念，即血浆性类固醇的生物可利用部分是未与血浆蛋白结合的部分。
