Radioimmunoassay of Plasma 17-Hydroxyprogesterone

Plasma 17-hydroxyprogesterone (17-OHP) was measured by radioimmunoassay, using an antibody preparation as specific binding reagent. One ml of plasma, with tritiated 17-OHP added for recovery estimation, was extracted with ether and chromatographed on a microcolumn of Celite. The interfering steroids in the 17-OHP fraction from the Celite column were removed by acetylation and rechromatography in the same system. The dried residue of the purified 17-OHP fraction was dissolved in assay buffer. Duplicate aliquots were run in the assay, in the presence of tritiated 17-OHP and diluted antiserum. Separation of free from bound hormone was achieved by dextran-coated charcoal suspension. Recovery of 3H-17-OHP ranged from 22 to 31%. The sensitivity in measuring unknown samples was 50 pg. The plasma levels of 17-OHP were measured in men and women. In 13 normal men, the 17-OHP ranged from 310 to 2170 pg/ml. In women, under various physiological conditions, the plasma levels of 17-OHP in pg/ml were: follicular pahase: 400±210 (mean±sd); luteal phase: 1560±740; Post menopause: 240±110; pregnancy (16–20 weeks): 1940 ±610. In 9 normal menstrual cycles studied daily, plasma 17-OHP levels showed a significant rise on the day of the midcycle LHFSH peak, being always above 1 ng/ml on that day.