Quality control study of estradiol and progesterone receptor determination

Lyophilized calf uterine tissue cytosol standards for estradiol receptor (ER) and progesterone receptor (PR), and freeze-dried tissue powders for PR determination were prepared. For the ER assay 4 standards were produced with no, low, medium, and high ER levels. The ER binding capacities (mean +/- SD) were low--261 +/- 46 (Brno) and 221 +/- 64 (Budapest), medium--451 +/- 100 and 340 +/- 59, high--712 +/- 139 and 581 +/- 102 fmol/mg protein, respectively. Two receptor-positive tissue powders and two positive cytosol standards in lyophilized form were used for the PR assay with receptor contents of 110, 148, 787, and 786 fmol/mg assayed in Brno, and 148, 250, 693, and 671 fmol/mg protein determined in Budapest. The stability of the standards was good for 10 months. All parameters tested in the two laboratories (specific binding capacities, Kd values, variation coefficients of the results) were in good correlation. Lyophilized calf uterine cytosol standards for ER and PR, and freeze-dried tissue powders for PR proved to be suitable materials for interlaboratory quality control of steroid receptor determination.