The plasma unconjugated estrone (E1) concentration has been measured in <5 ml plasma by a radio-ligand technique as we described for 17β-estradiol (E2), employing the soluble rabbit uterine estrogen binding protein as specific reagent, and activated charcoal to separate bound from free radioactive hormone (in this case, tritiated E1). Chromatography of a plasma extract on a celite column separated E1 and E2, which were assayed separately. The E1 blank was usually <10 pg/ml. The assay sensitivity was 25 pg and the sd of between assay duplicates was 7.7 pg/ml. Plasma E1 concentrations were: 17 normal males 62.2±6.6 se pg/ml, 15 post-menopausal women 40.1±5.7 se pg/ml. A distinct diurnal variation of plasma E1 concentrations was observed in each of 5 studies with a nadir at 12–4 am. Daily E1 and E2 measurements were made during 4 menstrual cycles. Both the preovulatory rise and luteal elevations noted for E2 were seen for E1. Utilizing this ligand binding approach both E1 and E2 may be measured in the same 3–5 ml plasma sample, so that both hormones may be studied repeatedly.
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Tulchinsky et al. (1970) studied this question.