Dancis J, Jansen V, Levitz M, Rosner W
J Clin Endocrinol Metab. 1978 Jun;46(6):863-8. doi: 10.1210/jcem-46-6-863.
The transfer and metabolism of cortisol and cortisone and the effect of protein binding on these processes have been investigated in vitro in the perfused human placenta. The clearance of cortisol in buffer, expressed as a fraction of the antipyrine transfer rate (clearance index), was 0.50 +/- 0.05 SEM in either direction. Extensive conversion to cortisone (85%) occurred during transfer. Addition of corticosteroid-binding globulin (CBG) in amounts sufficient to bind 50% of the cortisol reduced the clearance (0.40 +/- .026) insignificantly, whereas human serum albumin (HSA) in amounts sufficient to bind 50% of the cortisol reduced the clearance to 0.28 +/- 0.012 (P less than 0.001) even though the association constant for albumin is approximately 1000-fold less. The percent of conversion to cortisone did not change significantly with protein binding. The clearance index of cortisone from a protein-free perfusate was 0.74. With CBG and albumin in the same concentrations as used in the cortisol experiments, the binding of cortisone to CBG was 23% and its clearance was 0.70; with albumin, the binding was 45% and the clearance index was 0.45. The addition of albumin and CBG to the same perfusate resulted in a cortisol clearance equal to that obtained with perfusate containing only albumin. Binding to albumin may be more significant than binding to CBG in controlling the transfer rate of cortisol to the fetus.
在灌注的人胎盘中对皮质醇和可的松的转运与代谢以及蛋白质结合对这些过程的影响进行了体外研究。缓冲液中皮质醇的清除率，以安替比林转运率的分数表示（清除指数），双向均为0.50±0.05标准误。转运过程中发生了大量向可的松的转化（85%）。加入足以结合50%皮质醇的皮质类固醇结合球蛋白（CBG），清除率降低不显著（0.40±0.026），而加入足以结合50%皮质醇的人血清白蛋白（HSA），清除率降至0.28±0.012（P＜0.001），尽管白蛋白的结合常数约小1000倍。向可的松的转化率随蛋白质结合未发生显著变化。无蛋白灌注液中可的松的清除指数为0.74。使用与皮质醇实验相同浓度的CBG和白蛋白时，可的松与CBG的结合率为23%，其清除率为0.70；与白蛋白结合时，结合率为45%，清除指数为0.45。向同一灌注液中加入白蛋白和CBG导致的皮质醇清除率与仅含白蛋白的灌注液所获结果相同。在控制皮质醇向胎儿的转运速率方面，与白蛋白的结合可能比与CBG的结合更重要。
