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Original Studies |
Division of Endocrinology and Metabolism, Department of Internal Medicine III, University of Vienna, Vienna, Austria
Address all correspondence and requests for reprints to: H. Vierhapper, Clinical Division of Endocrinology and Metabolism, Department of Internal Medicine III, Währinger Gürtel 18–20, A-1090 Wien, Austria. E-mail: h.vierhapper{at}akh-wien.ac.at
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Abstract |
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,2-d-Testosterone (20 µg/h) was infused for 10 h
(0800–1800 h). Blood samples obtained at 20-min intervals from
1400–1800 h were pooled during two 2-h periods. Subsequently, each
volunteer received a daily dose of biosynthetic human GH (4 IU/day sc)
for 7 days. This resulted in a rise in plasma concentrations of
somatomedin-C from, basal, 0.67 ± 0.13 U/mL to 1.20
± 0.2 U/mL on day 7 (P < 0.0001). Testosterone
production rates (basal: 209.9 ± 31.0 µg/h) were unchanged by
treatment with GH (day 7: 192.2 ± 30.1 µg/h). In healthy men,
short-term treatment with sc GH does not influence endogenous
testosterone production rates. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Seven healthy, nonobese men aged 23–34 yr, who had been
carefully informed about the aims and the possible risks of the study,
gave their written consent to participate in this investigation. The
study protocol was accepted by the local ethics committee. On the day
of the experiments, an indwelling catheter was inserted into an
antecubital vein. Plasma samples were obtained for the determination of
somatomedin-C, and a constant (40 mL/h) iv infusion of
1,2-d-testosterone (CIL Isotopes,
Andover, MA) (0.25 mg in 500 mL 0.9% saline also containing 2 mL of
the individual’s own blood) was started at 0800 h. At the
beginning and at the end of each infusion a sample of the infusate from
the end of the infusion line was obtained to determine losses by
adsorption. Hence actual individual infusion rates (20 ± 4
µg/h) were determined retrospectively. After an equilibration period
of 6 h (at 1400 h) a second indwelling catheter was inserted
into the contralateral arm, and blood samples were obtained from
1400 h until 1800 h at 20-min intervals. These blood samples
were subsequently pooled for two 2-h periods, and pooled samples were
used for analysis.
Starting with the following day, each volunteer received a daily dose of biosynthetic human GH (Genotropin, Pharmacia-Upjohn, Vienna, Austria) (4 IU/day sc) at 0800 h for 7 days. On day 7, the determination of cortisol production rates was repeated as described above.
Materials
All organic solvents were of high performance liquid
chromatography grade and were purchased from Baker
Chemicals, Phillipsburg, NJ. Nonactive testosterone
(17ß-hydroxy-4-androsten-3-one) was obtained from
Steraloids (Wilton, NH). Radioactive
[3H]1,2,6,7-testosterone (SA 100 Ci/mmol) and
stable-labeled 1,2-d-testosterone (isotopic enrichment:
99.0%) were purchased from New England Biolabs, Inc.
(Boston, MA) and from CIL Isotopes, Andover, MA,
respectively.
Plasma concentrations of somatomedin-C (insulin-like growth factor I) were determined radioimmunologically with a commercially available kit (Immundiagnostik, Benheim, Germany). Intra- and interassay coefficients of variation were less than 15%
Sample preparation and analysis by gas chromatography-mass spectrometry (GC-MS)
Plasma samples (5.0 mL) supplemented with 20000 dpm of [3H]testosterone for later control of recovery and with 20 mL of 0.5% trifluoric acetic acid (TFA) were applied to Sep-Pak C-18 cartridges (500 mg) (Waters/Millipore Corp., Milford, MA) pretreated with successive application of 5.0 mL methanol, 5.0 mL ethyl acetate, 20 mL water, and 5.0 mL TFA (0.5% wt/vol). Following sample application, the cartridges were first treated with 3x 5.0 mL TFA (0.5% wt/vol). Testosterone was subsequently eluted by ethyl acetate (2 x 1.0 mL), dried under a stream of nitrogen at 37 C, reconstituted in 100 µL CH2Cl2, and further prepurified by thin-layer chromatography (chloroforme/acetone = 70:30). The zone containing testosterone was eluted (2x 2.5 mL methanole) and supplemented with 10 ng dehydrotestosterone (1,4-androstadien-17ß-ol-3-one) as an internal standard for GC-MS analysis. Derivatization was subsequently performed with heptafluorobutyric anhydride: acetone (1:4; time = 60 min) at room temperature. Analysis by GC-MS (Finnigan MAT95 equipped with a 25-m CB5 fused silica column; San Jose, CA) was then performed using S.I.M. mode and electric ionization (resolution 6000). The tracer ions were (m/e 678 (dehydrotestosterone; internal standard), m/e 680 (native testosterone), and m/e 682 (1,2-d-testosterone). The sensitivity at a peak to noise ratio of 10:1 was less than 100 fg.
Calculation of testosterone production rate
Production rates of testosterone (PR[T]) were calculated from the product of the known infusion rate (Rt) and the ratio of tracer infusate enrichment (Et) to tracer dilution in the plasma (Es): (PR[T] = Rt x (Et/Es-1) (4).
Statistical analyses
Data are given as means ± SD. Student’s t test (two-tailed) for matched pairs was used for statistical analysis.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The administration of biosynthetic GH resulted in a rise in plasma concentrations of somatomedin-C from basal levels of 0.67 ± 0.13 U/mL to 1.20 ± 1.2 U/L on day 7 (P < 0.0001).
Production rates of testosterone (Table 1
)
Steady state concentrations of both exogenous (labeled) and endogenous (unlabeled) testosterone were comparable before and after 7 days of GH administration. Hence similar production rates of testosterone were calculated before (209.9 ± 31.0 µg/h) and after (day 7: 192.2 ± 30.1 µg/h) treatment with GH.
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Discussion |
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In regard to testosterone, GH has been shown to enhance the testicular responsiveness to gonadotropins on testosterone production in premature rats (7). This observation is in keeping with the known delay in the onset of puberty in patients with isolated GH deficiency (8, 9) and the reported acceleration of pubertal maturation during GH substitution therapy in these adolescent patients (10). Although GH therefore may enhance the responsiveness of immature Leydig cells, the available data fail to provide such evidence in adult human beings. In a group of healthy men, an increase in serum testosterone concentrations was seen during somatostatin-induced suppression of GH secretion (11), although the observed effect could also have been caused by a direct testicular effect of the used somatostatin analog. In a small group of undernourished subjects, plasma concentrations of testosterone were found to be unchanged by GH administration (12).
Using the stable-labeled isotope dilution technique and GS-MS analysis, we recently demonstrated that short-term application of pharmacological doses of GH induces a fall in endogenous cortisol production rates in healthy men. The results of the present study, which were obtained in an analogous fashion, indicate that, as opposed to cortisol, production rates of testosterone are not diminished by GH in healthy men. Production rates of testosterone were in the same range as reported previously (2) before and after exogenous GH administration, although the dose of GH used (4 U/day) exceeded the doses usually employed therapeutically. Because the potential therapeutic benefit of GH in adults is mainly caused by its anabolic action, the lack of a suppressive effect on the production of testosterone, another anabolic hormone, is reassuring.
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Acknowledgments |
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Footnotes |
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Received June 5, 1998.
Accepted July 7, 1998.
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References |
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