title: The metabolism of androstenedione in human pregnancy: the use of constant infusion of unlabeled steroid to assess its metabolic clearance rate, its production rate, and its conversion into androgens and estrogens.
abstract: Using constant infusion of unlabeled steroid, we have studied the metabolic clearance rate (MCR), half-life (T 1/2), and conversion ratio of androstenedione (A) into androgens and estrogens throughout human pregnancy. In nonpregnant women, results obtained by infusion of unlabeled A were identical to those obtained by the infusion of either labeled steroid or a mixture of labeled and unlabeled steroid. A twofold increase in the infusion rate did not change any of these results, indicating that enzyme availability was not a limiting step. When compared to the nonpregnant state, pregnancy was associated with a twofold rise in plasma A production rate (PR) (p less than 0.05) but with minimal changes in its MCR or its T 1/2, thus leading to a twofold increase in the plasma concentration of A (p less than 0.05). The conversion of A into testosterone (T) rose twofold at term pregnancy (p less than 0.05), whereas that of A into estrone (E1) rose fivefold (p less than 0.01) and that of A into estradiol (E2) rose 16 fold (p less than 0.001). It is concluded that constant infusions of unlabeled A can be used successfully to study the kinetics of A when one is reluctant to infuse isotopic steroid.
mesh_terms: D000328:Adult; D000728:Androgens / Q000097:blood*; D000735:Androstenedione / Q000008:administration & dosage / Q000378:metabolism*; D003687:Dehydroepiandrosterone / Q000097:blood; D004958:Estradiol / Q000097:blood; D004967:Estrogens / Q000097:blood*; D004970:Estrone / Q000097:blood; D005260:Female; D006207:Half-Life; D006801:Humans; D008657:Metabolic Clearance Rate; D011247:Pregnancy; D013739:Testosterone / Q000097:blood; D014316:Tritium
chemical_list: D000728:Androgens; D004967:Estrogens; D014316:Tritium; D004970:Estrone; D013739:Testosterone; D000735:Androstenedione; D003687:Dehydroepiandrosterone; D004958:Estradiol