title: Testosterone metabolic clearance and production rates determined by stable isotope dilution/tandem mass spectrometry in normal men: influence of ethnicity and age.
abstract: The metabolic clearance rate (MCRT) and production rate (PRT) of testosterone (T) were measured using constant infusion of trideuterated (d3) T and quantitating serum d3T by liquid chromatography-tandem mass spectrometry (LC-MS-MS). Serum unlabeled T (d0T) was measured by LC-MS-MS, and serum total T (d3T + d0T) was measured by RIA. Mean MCRR (measured by LC-MS-MS) in young white men (1272 +/- 168 liters/d) was not significantly different from young Asian men (1070 +/- 166 liters/d). Mean PRT was also not significantly different between the two ethnic groups (whites, 9.11 +/- 1.11 mg/d; Asians, 7.22 +/- 1.15 mg/d; P = 0.19 using d0T data). Both the mean MCRR (812 +/- 64 liters/d; P < 0.01) and the PRT (3.88 +/- 0.27 mg/d; P < 0.001) were significantly lower in middle-aged white men when compared with their younger counterparts. The mean MCRR and PRR calculated using serum total T or d0T data showed a diurnal variation, with levels at midday significantly higher than those measured in the evening in the young (MCRT, P < 0.01; PRT, P < 0.001) and to a lesser extent in the older men (MCRT, P < 0.05; PRT, P < 0.05 using total T and P < 0.001 using d0T data). We conclude that using LC-MS-MS to detect d3T in serum after constant infusion of stable isotope-labeled T allows the measurements of MCRT and PRT, which can be used to study androgen metabolism repeatedly after physiological or pharmacological interventions.
authors.affiliation: Department of Medicine, Harbor-University of California Los Angeles Medical Center and Research and Education Institute, Torrance, California 90509, USA. wang@gcrc.rei.edu
authors.forename: Christina
authors.initials: C
authors.lastname: Wang
authors.forename: Don H
authors.initials: DH
authors.lastname: Catlin
authors.forename: Borislav
authors.initials: B
authors.lastname: Starcevic
authors.forename: Andrew
authors.initials: A
authors.lastname: Leung
authors.forename: Emma
authors.initials: E
authors.lastname: DiStefano
authors.forename: Geraldine
authors.initials: G
authors.lastname: Lucas
authors.forename: Laura
authors.initials: L
authors.lastname: Hull
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Swerdloff
mesh_terms: D000328:Adult; D044466:Asian People; D003903:Deuterium; D006801:Humans; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D013737:Testis / Q000378:metabolism*; D013739:Testosterone / Q000493:pharmacokinetics*; D044465:White People
chemical_list: D013739:Testosterone; D003903:Deuterium