Diffusion Advection k3||k4 2
► Binding Metabolism
Fig. 10. (Continued) (B) Schema of fate of secreted testosterone in plasma. (Unpublished line drawing.)
Developing concepts of time-adaptive control of testosterone secretion incorporate interactions among GnRH, LH, and testosterone. Homeostasis requires reversible, recurrent, and reciprocal (feedback and feedforward) adjustments to external stress (e.g., food deprivation and trauma) and internal needs (e.g., anabolism and procreation). In this ensemble perspective, no single gland acts alone. Clinical studies in the healthy aging male point to regulatory failure of GnRH-driven pulsatile LH secretion, LH-stimulated Leydig cell androgen biosynthesis, and testosterone-enforced feedback on GnRH/LH outflow. Accordingly, hypoandrogenemia in the older male is the final common consequence of a matrix of primary and secondary deficits in the hypothala-mic-pituitary-gonadal ensemble.
1. Stearns EL, MacDonald JA, Kaufman BJ, et al. Declining testicular function with age, hormonal and clinical correlates. Am J Med 1974;57:761-766.
2. Davidson JM, Chen JJ, Crapo L, Gray GD, Greenleaf WJ, Catania JA. Hormonal changes and sexual function in aging men. J Clin Endocrinol Metab 1983;57:71-77.
3. Wang C, Alexander G, Berman N, et al. Testosterone replacement therapy improves mood in hypogo-nadal men—a clinical research center study. J Clin Endocrinol Metab 1996;81:3578-3583.
4. Morley JE, Perry HM, Kaiser FE, et al. Effects of testosterone on replacement therapy in old hypogo-nadal males: a preliminary study. J Am Geriatr Soc 1993;41:149-152.
5. Urban RJ, Bodenburg YH, Gilkison C, et al. Testosterone administration to elderly men increases skeletal muscle strength and protein synthesis. Am J Physiol 1995;269:E280-E286.
6. Barrett-Connor E, Von Muhlen DG, Kritz-Silverstein D. Bioavailable testosterone and depressed mood in older men: the Rancho Bernardo study. J Clin Endocrinol Metab 1999;84:573-577.
7. Barrett-Connor E, Goodman-Gruen D, Patay B. Endogenous sex hormones and cognitive function in older men. J Clin Endocrinol Metab 1999;84:3681-3685.
8. Abbasi AA, Drinka PJ, Mattson DE, Rudman D. Low circulating levels of insulin-like growth factors and testosterone in chronically institutionalized elderly men. J Am Geriatr Soc 1993;41:975-982.
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