Determination of Serum Cortisol Fractions by Isocolloidosmolar Equilibrium Dialysis. Changes during Pregnancy

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概要

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• A modified equilibrium dialysis method to determine the percentage of protein-unbound cortisol in the total serum cortisol (unbound cortisol %) was devised. When serum was dialyzed against an ordinary buffer solution, unbound cortisol% increased with the time of dialysis, accompanying a progressive decrease in serum protein concentration. These changes seemed to be due to the difference of colloidal osmotic pressure between the serum and the buffer. An addition of3% dextran in the buffer resulted in a stable equilibrium and both the unbound cortisol% and the protein concentration stayed unchanged after12hr of the dialysis. Therefore, the determination of unbound cortisol % was carried out by dialyzing serum against 3% dextran buffer for18hr and the method was called an isocolloidosmolar equilibrium dialysis. Dextran did not bind cortisol at all. Additions of graded amounts of cortisol in the dialysate caused significant increases in unbound cortisol % of a pooled serum. The ratio of unbound cortisol to albumin-bound cortisol was determined by the same dialysis system using heat-treated serum in the presence of nonradioactive cortisol. A combination of these two determinations enables to assess concentrations of unbound, albumin-bound and transcortin-bound cortisol in serum. Both intra-assay and inter-assay precisions of these methods were excellent (at most±4.65%).<BR>In normal subjects (cortisol concentration: 7.1±2.5μg/100m<I>l</I>), 5.8±0.7% was present as unbound cortisol, 15.8±2.5% as albumin-bound and78.3±2.8% as transcortin-bound cortisol. Concentrations of all serum cortisol fractions increased with the course of pregnancy, however, relative increment of transcortin-bound cortisol was larger than that of total cortisol, while those of unbound and albumin-bound cortisol were far less. Percentages of transcortin-bound and albumin-bound cortisol changed in parallel to changes in concentrations of these cortisol-binding proteins during pregnancy.<BR>pregnancy. The method requires a small amount of serum and is applicable to determine three cortisol fractions in individual sera.

• 社団法人 日本内分泌学会の論文

著者

• Seo Hisao

  The Research Institute Of Environmental Medicine Nagoya University

• Matsui Nobuo

  The Research Institute Of Environmental Medicine Nagoya University

• YAMAMOTO MASAHIRO

  The Research Institute of Environmental Medicine, Nagoya University

• ARIYOSHI YUTAKA

  The Research Institute of Environmental Medicine, Nagoya University

• NIINOMI MITSURO

  The Research Institute of Environmental Medicine, Nagoya University

• MATSUI NOBUO

  The Research Institute of Environmental Medicine, Nagoya University

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