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.
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.
mesh_terms: D000328:Adult; D002369:Castration; D003687:Dehydroepiandrosterone / Q000097:blood / Q000378:metabolism*; D005260:Female; D006207:Half-Life; D006801:Humans; D007044:Hysterectomy; D007553:Isotope Labeling; D008598:Menstruation; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D011247:Pregnancy; D014316:Tritium
chemical_list: D014316:Tritium; D003687:Dehydroepiandrosterone