A double competitive binding method of measuring oestradiol from menstrual cycle plasma with and without the prior purification of oestradiol.

Abstract

ABSTRACT Oestradiol was determined in menstrual cycle plasma by a double competitive binding assay method applied with and without TLC purification of the steroid. The evaporated ether extract from plasma or from the oestradiol zone of a thin layer plate was incubated with a limited excess of rabbit uterine cytosol containing oestradiol receptor. The specificity and affinity of the receptor protein ensured the preferential binding of oestradiol to the virtual exclusion of other oestrogens and weak contaminating competitors introduced by the procedure. These unbound compounds were removed by charcoal incubation. The remaining supernatant was heat-treated to denature the receptor protein and the released oestradiol was determined by competitive binding with rabbit uterine oestradiol receptors. The methods have the advantage of high specificity; the direct assay which excludes the TLC step, is rapid, sensitive and suitable for the routine examination of normal menstrual cycles.