The determination of maternal and foetal rat plasma corticosterone concentration in late pregnancy by competitive protein binding analysis.

A procedure for the determination of corticosterone in 20 microliters of rat plasma, in maternal and foetal late pregnancy with a protein binding radioassay, is described. The method is suitable in a range of 0.5-3 ng of corticosterone. An amount of 0.5 ng can be detected with a coefficient of variation for duplicate of 13%. This procedure seems to be specific for glucocorticosteroids. The comparison of the results obtained with fluorimetry and the competitive protein binding radioassay show the reliability of both methods although the protein binding radioassay is much more sensitive.