Agrimonti F, Frairia R, Fornaro D, Torta M, Borretta G, Trapani G, Bertino E, Angeli A
Chronobiologia. 1982 Jul-Sep;9(3):281-90.
It has been demonstrated that human milk contains a corticosteroid-binding globulin (CBG, transcortin) which is very similar to that isolated from plasma. It is agreed, moreover, that the cortisol environment of the breast is important for the synthesis of major milk proteins. It was of interest, therefore, to investigate whether milk transcortin exhibits circadian variations in the binding activity as does the plasma counterpart. Twelve lactating women, aged 23-35 years, collected specimens of milk just before feeding at different times of the 24-h cycle for 3 consecutive days in the first week of lactation. Six women extended milk collection for at least a 28-days span in the first 2 months of lactation. To obtain whey, milk was centrifuged in cellulose nitrate tubes at 105,000 g for 30 min at 4 degrees C. Specific cortisol binding activity of CBG was measured by an adsorption technique and data were expressed as a function of protein content. Cortisol levels in milk were measured by radioimmunoassay. Rhythmometric analyses (single- and mean-cosinor procedures) yielded detection of a significant circadian rhythm in 'apparent specific binding activity' for cortisol (ASBA-F) whereas no significant oscillation was found as far as milk cortisol concentrations were concerned. Mean acrophase of the CBG-binding activity in milk was located in the evening, lagging behind the corresponding activity in serum by approximately 8 h. A circaseptan rhythmicity in milk binding activity was also present in our longitudinal series at a high level of significance. These results provide evidence that CBG binding activity in human milk has a clear circadian rhythm in the face of ecchronic milk cortisol concentrations. Phase-shift with regard to the rhythm of the plasma counterpart may be accounted for by processes of milk accumulation before nursing The significance of circadian and circaseptan variations in specific cortisol (and other steroids) binding in milk awaits further investigation.
已证明人乳中含有一种皮质类固醇结合球蛋白（CBG，转皮质素），它与从血浆中分离出的该蛋白非常相似。此外，人们一致认为乳腺的皮质醇环境对主要乳蛋白的合成很重要。因此，研究乳转皮质素的结合活性是否像血浆中的对应物那样呈现昼夜变化就很有意义了。12名年龄在23至35岁的哺乳期妇女，在哺乳期第一周连续3天在24小时周期的不同时间喂奶前采集乳汁样本。6名妇女在哺乳期的前两个月将乳汁采集时间延长至至少28天。为了获得乳清，将乳汁在硝酸纤维素管中于4℃以105,000 g离心30分钟。通过吸附技术测量CBG的特异性皮质醇结合活性，并将数据表示为蛋白质含量的函数。通过放射免疫测定法测量乳汁中的皮质醇水平。节律分析（单余弦和平均余弦程序）显示皮质醇的“表观特异性结合活性”（ASBA-F）存在显著的昼夜节律，而乳汁皮质醇浓度方面未发现显著波动。乳汁中CBG结合活性的平均峰相位位于傍晚，比血清中的相应活性滞后约8小时。在我们的纵向研究系列中，乳汁结合活性也存在显著的七天节律。这些结果证明，尽管乳汁皮质醇浓度持续存在，但人乳中CBG结合活性具有明显的昼夜节律。相对于血浆对应物节律的相位偏移可能是由于哺乳前乳汁积累过程所致。乳汁中特异性皮质醇（和其他类固醇）结合的昼夜和七天变化的意义有待进一步研究。
