Unbound Plasma Cortisol in Pregnant and Enovid-E Treated Women as Determined by Ultrafiltration1

Abstract

Unbound plasma cortisol concentrations were determined in nonpregnant, pregnant and Enovid-E treated women. A method is described for the measurement of the unbound fraction using ultrafiltration by centrifugation at 37 C to obtain a filtrate of 1/10 the volume of the plasma sample. Tracer amounts of cortisol-³H were added to determine the per cent of cortisol filterable. Total cortisol concentrations were measured by a fluorometric technique. The mean unbound or ultrafilterable cortisol concentration for the pregnant women was 2.47 μg/100 ml, which is significantly higher (p<.001) than the mean of 1.00 μg/100 ml for the nonpregnant, and 1.31 μg/100 ml for the Enovid-E treated women. High concentrations of total plasma cortisol were present, as expected, in both the pregnant and the Enovid-E treated women, but the latter group had a significantly lower (p<.001) per cent filterable cortisol of 4.3% as compared to 6.3% for the pregnant women, and 7.6% for the nonpregnant women. The implications of the findings in pregnant women are briefly discussed.