Stability of estrogen- and progesterone-receptor concentrations in human uterus tissue

Homogeneous control specimens for estrogen receptor (ER) and progesterone receptor (PR) assays were prepared from freshly collected human uterus. After removal of the connective tissue, the specimen was washed with isotonic saline, cut into small pieces, quickly frozen in liquid nitrogen, and stored at -70 degrees C until analyzed. Cytosol prepared from this specimen was lyophilized and stored at -70 degrees C. A single step of reconstitution, with glycerol (100 mL/L) in water, is sufficient to prepare a control. Two specimens prepared this way were found to be reasonably stable for 20 months (first specimen, mean +/- SD: ER = 22.1 +/- 2.9 fmol/mg, PR = 136.5 +/- 26.9 fmol/mg; second specimen: ER = 107.2 +/- 11.7 fmol/mg, PR = 922 +/- 71.6 fmol/mg). Another specimen, prepared similarly but not frozen in liquid nitrogen soon after collection, was less stable; its ER and PR concentrations deteriorated faster.