期刊
EUROPEAN JOURNAL OF ENDOCRINOLOGY
卷 153, 期 4, 页码 577-586出版社
BIOSCIENTIFICA LTD
DOI: 10.1530/eje.1.02001
关键词
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资金
- NCRR NIH HHS [M01 RR00585, M01 RR000585] Funding Source: Medline
- NIA NIH HHS [K01 AG019164, R01 AG19695, K01 AG19164] Funding Source: Medline
Objective: Testosterone supplementation increases GH and IGF-I concentrations in healthy older men via unknown mechanisms. We examine the hypotheses that (i) testosterone amplifies stimulation of GH secretion by GH-releasing peptide (GHRP)-2 or GH-releasing hormone (GHRH) infused with L-arginine to limit somatostatin outflow (i.e. upregulates each agonistic pathway), (ii) testosterone augments the effect of both peptidyl secretagogues infused together (i.e. reduces opposition by hypothalamic somatostatin) and (iii) abdominal visceral fat (AVF) mass is a negative determinant of specific secretagogue-stimulated GH secretion. Design: Randomized double-blind crossover design of placebo versus testosterone administration in healthy older men. Methods: Deconvolution analysis was used to estimate basal GH secretion and the mass (integral) and waveform (time-shape) of GH secretory bursts. Results: Statistical contrasts revealed that administration of testosterone compared with placebo in seven men aged 60-77 years increased fasting concentrations of GH (P < 0.01) and IGF-I (P = 0.003). and basal (P < 0.005) and pulsatile (P < 0.01) GH secretion. Testosterone did not after the absolute value or rank order of secretagogue efficacy: L-arginine/GHRP-2 (23-fold effect over saline) = GHRH/GHRP-2 (20-fold) > L-arginine/GHRH (7.5-fold). Waveform reconstruction indicated that each stimulus pair accelerated initial GH secretion within a burst (P < 0.01). Regression analysis disclosed a significant inverse association between GH secretory-burst mass and computer tomography-estimated AVF following stimulation with L-arginine/GHRH after testosterone supplementation (R-2 = 0.54, P = 0.015). Conclusion: Supraphysiological testosterone concentrations augment GH and IGF-I production in the elderly male without altering maximal somatotrope responses to single and combined GHRH and GHRP-2 drive, thus predicting multifactorial mechanisms of testosterone upregulation.
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