A fast and convenient method for determining estrogen receptor using rabbit uterus as a standard

A fast and convenient method is described for the determination of estrogen receptors (ERs). This method involves the use of rabbit uterus as a standard. ER content of the rabbit uterus powder was determined using the conventional methods, i.e., Scatchard plot and sucrose density gradient methods. The rabbit uterus cytosol was serially diluted to give a range of protein concentrations from 1 to 0.062 mg/ml. A standard curve was thus generated with the corresponding ER concentrations, and this curve was used for the determination of ERs in breast tumors. The method involved incubating the standards with 125I-estradiol and subsequent removal of the free radiolabeled estradiol using dextran-coated charcoal. A parallel sample was also incubated with diethylstilbestrol. A standard curve was obtained between the 125I-estradiol percentage of binding and the corresponding ER concentration. Tumor cytosols were also treated in a similar manner, and the receptor content was determined from the standard curve. Excellent correlation was obtained between this method and other conventional methods. This method is simpler and less time consuming, and up to ten tumors can be analyzed at one time. It is especially useful when limited amounts of tumor tissue are available, as a concentration of only 1 mg of protein per ml is required.