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  • Title: The use of constant infusion of unlabeled dehydroepiandrosterone for the assessment of its metabolic clearance rate, its half-life, and its conversion into estrogens.
    Author: Bélisle S, Schiff I, Tulchinsky D.
    Journal: J Clin Endocrinol Metab; 1980 Jan; 50(1):117-21. PubMed ID: 6444220.
    Abstract:
    We have exploited the feasibility of utilizing constant infusion of unlabeled dehydroepiandrosterone (DHEA) for calculating its MCR, its half-life (t1/2), and its conversion ratio into estrogens. In nonpregnant women, results obtained by infusion of unlabeled DHEA were similar to those obtained by the infusion of either labeled steroid or a mixture of labeled and unlabeled steroid. An increase of 3-fold in the infusion rate did not change any of these results, indicating that enzyme availability was not a limiting step in the production of estradiol (E2) from DHEA. When compared to the nonpregnancy state, term pregnancy was not associated with a change in plasma DHEA concentrations, but the MCR of DHEA of 76.8 +/- 18.8 (SE) liters/kg.day was 2.5-fold higher and the t1/2 of 22.5 +/- 3.6 min was 2-fold lower. The conversion ratio of DHEA into E2 increased during pregnancy by 500-fold, and DHEA contributed 9% of maternal circulating E2. In the first postpartum day, the MCR of DHEA and its t1/2 were not significantly different from those of term pregnancy, suggesting that the increased MCR of DHEA in pregnancy was not solely due to increased clearance of DHEA by the placenta.
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