Radioimmunoassay of Plasma Progesterone

Abstract

A radioimmunoassay for the measurement of plasma progesterone is described. The 21-hemisuccinate of 11-desoxycortisol was coupled to human serum albumin using carbodiimide, and the conjugate was used to immunize 2 ewes. The antiserum obtained after 8 months of immunization from one of the ewes was used in the assay procedure. Incubation at 4 C overnight of this diluted antiserum was carried out in the presence of 1,2-3H-17-hydroxyprogesterone. Separation of free from bound hormone was achieved by a dextran-coated charcoal suspension. One ml of plasma or serum, with tritiated progesterone added for recovery, was extracted with ether, then chromatographed on a microcolumn of Celite. Recovery of 3H-progesterone after extraction and chromatography was 84.2±4.8% (sd). The sensitivity varied between 10 and 25 pg of progesterone. Recovery experiments of progesterone added to water and plasma confirmed accuracy. Concentration of progesterone in plasma from men averaged 233±64 (sd) pg/ml and from postmenopausal women 180±63 (sd) pg/ml. During the follicular and midluteal phases of the menstrual cycle, the levels of plasma progesterone were, respectively: 545±103 pg/ml (mean±sd) and 8561±4661 pg/ml. During pregnancy, the plasma level of progesterone varied with the stages of pregnancy, being 48.4±18 ng/ml (mean ±sd) at 16–18 weeks of gestation, 98.0±28 at 28–30 weeks and 178.5±48 at term.