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Testosterone dose-response relationships in healthy young men.
Bhasin S, Woodhouse L, Casaburi R, Singh AB, Bhasin D, Berman N, Chen X, Yarasheski KE, Magliano L, Dzekov C, Dzekov J, Bross R, Phillips J, Sinha-Hikim I, Shen R, Storer TW.
Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University of Medicine and Science, Los Angeles, CA 90059, USA.
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Testosterone increases muscle mass and strength and regulates other physiological processes, but we do not know whether testosterone effects are dose dependent and whether dose requirements for maintaining various androgen-dependent processes are similar. To determine the effects of graded doses of testosterone on body composition, muscle size, strength, power, sexual and cognitive functions, prostate-specific antigen (PSA), plasma lipids, hemoglobin, and insulin-like growth factor I (IGF-I) levels, 61 eugonadal men, 18-35 yr, were randomized to one of five groups to receive monthly injections of a long-acting gonadotropin-releasing hormone (GnRH) agonist, to suppress endogenous testosterone secretion, and weekly injections of 25, 50, 125, 300, or 600 mg of testosterone enanthate for 20 wk. Energy and protein intakes were standardized. The administration of the GnRH agonist plus graded doses of testosterone resulted in mean nadir testosterone concentrations of 253, 306, 542, 1,345, and 2,370 ng/dl at the 25-, 50-, 125-, 300-, and 600-mg doses, respectively. Fat-free mass increased dose dependently in men receiving 125, 300, or 600 mg of testosterone weekly (change +3.4, 5.2, and 7.9 kg, respectively). The changes in fat-free mass were highly dependent on testosterone dose (P = 0.0001) and correlated with log testosterone concentrations (r = 0.73, P = 0.0001). Changes in leg press strength, leg power, thigh and quadriceps muscle volumes, hemoglobin, and IGF-I were positively correlated with testosterone concentrations, whereas changes in fat mass and plasma high-density lipoprotein (HDL) cholesterol were negatively correlated. Sexual function, visual-spatial cognition and mood, and PSA levels did not change significantly at any dose. We conclude that changes in circulating testosterone concentrations, induced by GnRH agonist and testosterone administration, are associated with testosterone dose- and concentration-dependent changes in fat-free mass, muscle size, strength and power, fat mass, hemoglobin, HDL cholesterol, and IGF-I levels, in conformity with a single linear dose-response relationship. However, different androgen-dependent processes have different testosterone dose-response relationships.
Table 2. Serum total and free testosterone, LH, FSH, SHBG, and IGF-I levels
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Testosterone
Dose Baseline Week 16 Change from Baseline P vs. Zero Change
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Testosterone (ng/dl) (overall ANOVA P = 0.0001)
25 mg 593 ± 48 253 ± 66 340 ± 85 0.0029
50 mg 566 ± 78 306 ± 58 260 ± 64 0.0037
125 mg 553 ± 53 570 ± 75 57 ± 75 0.7425
300 mg 653 ± 50 1,345 ± 139 691 ± 143 0.0005
600 mg 632 ± 63 2,370 ± 150 1,737 ± 156 0.0001
Free testosterone (pg/ml) (overall ANOVA P = 0.0001)
25 mg 62 ± 6 29 ± 5 33 ± 8 0.0014
50 mg 57 ± 6 32 ± 3 25 ± 5 0.0009
125 mg 49 ± 5 52 ± 8 3 ± 7 0.8601
300 mg 71 ± 7 138 ± 21 67 ± 18 0.0012
600 mg 64 ± 5 275 ± 30 211 ± 31 0.0001
LH (U/l) (overall ANOVA P = 0.8054)
25 mg 3.5 ± 0.4 0.3 ± 0.1 3.2 ± 0.4 0.0001
50 mg 3.8 ± 0.3 0.6 ± 0.3 3.0 ± 0.4 0.0008
125 mg 3.4 ± 0.3 0.5 ± 0.1 2.8 ± 0.4 0.0001
300 mg 3.7 ± 0.5 0.6 ± 0.1 3.5 ± 0.5 0.0002
600 mg 3.3 ± 0.3 0.6 ± 0.4 2.9 ± 0.4 0.0001
SHBG (nmol/l) (overall ANOVA P = 0.0001)
25 mg 29.1 ± 2.9 28.5 ± 3.6 0.6 ± 2.9 0.8497
50 mg 24.4 ± 3.4 21.1 ± 3.2 3.3 ± 1.1 0.0202
125 mg 33.1 ± 4.2 28.9 ± 3.8 4.2 ± 2.6 0.1410
300 mg 31.4 ± 3.8 22.4 ± 3.9 9.1 ± 3.7 0.0348
600 mg 40.1 ± 4.9 20.6 ± 3.2 19.5 ± 2.8 0.0001
IGF-I (ng/ml) (overall ANOVA P = 0.0001)
25 mg 268 ± 26 261 ± 35 7 ± 19 0.7462
50 mg 246 ± 14 225 ± 12 20 ± 10 0.0797
125 mg 299 ± 24 282 ± 31 18 ± 17 0.3284
300 mg 314 ± 24 388 ± 30 74 ± 28 0.0272
600 mg 227 ± 20 304 ± 21 77 ± 13 0.0001
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Values on each day represent the mean (±SE) of all available values on that day. However, the change represents the difference between paired values only. Treatment values represent the day 113 (week 16) values, obtained 1 wk after the previous testosterone injection. We used week 16 rather than week 20 values because week 20 values were not always drawn exactly 1 wk after the previous injection. LH and FSH, luteinizing and follicle-stimulating hormones, respectively; SHBG, sex hormone-binding globulin; IGF-I, insulin-like growth factor I. To convert total testosterone levels to nmol/l, multiply by 0.03467. To convert free testosterone levels to pg/ml, multiply by 3.467