Effects of time and steroid concentration on binding of C14-estrogens in human plasma.

Abstract

16-C14-estrone and 16-C14-estradiol-17β were injected intravenously into normal human subjects. C14-estrogens were injected either alone or following infusion of 50 mg unlabeled progesterone or estradiol-17β. Blood samples were drawn at 30 minutes and at 120 or 180 minutes after injection. The blood plasma was fractionated by the cold ethanol fractionation techniques and plasma fractions were examined for radioactivity. The delay of time of phlebotomy resulted in an increase in percentage of conjugated metabolites. Injection of a large amount of estradiol-17β resulted in a more rapid disappearance of conjugated radioactive metabolites of C14-estradiol-17β in both protein-bound and unbound forms. No pronounced changes in distribution of radioactivity among the various plasma fractions occurred as a result of prior administration of large amounts of unlabeled steroid.