title: Metabolic clearance rate and interconversion of androgens and the influence of the free androgen fraction.
abstract: Using the continuous infusion technique, the conversion ratios (CR) of testosterone (T) to androstenedione (A) and dihydrotestosterone (DHT) and of A to T and DHT were determined in 12 normal males (aged 31-72 yr), 10 normal postmenopausal women, and 4 amenorrheic women with idiopathic hirsutism; in 4 additional males these studies were performed during infusion of cold T to increase plasma T to supraphysiological levels. It was observed that besides the MCR of T and DHT, the blood conversion ratios (CRBB) of T in A and to a lesser extent of T in DHT were also significantly correlated with either the free or the nontestosterone-estradiol-binding globulin-bound T fraction but not with total plasma T. In postmenopausal women, plasma A was by far the most important precursor of plasma DHT; the CRA/DHTBB was significantly higher than CRT/DHTBB. It is suggested that total plasma A, but only nonspecifically bound T, freely gains access into the cells where these conversions occur and that plasma A might be an important parameter of androgenicity. Less than 50% of plasma DHT could be accounted for by peripheral conversion of either A or T. Whereas in males this may be explained by direct DHT secretion, in (postmenopausal) women conversion of other precursors to plasma DHT should be considered.
mesh_terms: D000328:Adult; D000368:Aged; D000568:Amenorrhea / Q000097:blood; D000735:Androstenedione / Q000097:blood*; D013196:Dihydrotestosterone / Q000097:blood*; D005260:Female; D006628:Hirsutism / Q000097:blood; D006801:Humans; D008297:Male; D008593:Menopause; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D013739:Testosterone / Q000097:blood*
chemical_list: D013196:Dihydrotestosterone; D013739:Testosterone; D000735:Androstenedione