title: Aging and declining testosterone: past, present, and hopes for the future.
abstract: As men age, serum testosterone (T) levels decline, whereas serum  luteinizing hormone (LH) levels increase somewhat or remain unchanged.  Age-related reductions in T levels may be associated with alterations in body  composition; energy level; muscle strength; physical, sexual, and cognitive  functions; and mood. The predominant contributor to the decline in serum T  levels is the decreased ability of the aging testes to make T. As in humans,  the Brown Norway rat demonstrates age-related reductions in serum T levels in  the setting of unchanged or modestly increased serum LH levels. In this rat  model, the ability of aged Leydig cells, the terminally differentiated  T-producing cells of the testis, to produce T in response to LH stimulation is  significantly diminished. This review begins with a discussion of what is  known of the molecular mechanisms by which T synthesis declines with Leydig  cell aging. It concludes with a brief history of T replacement therapy,  current guidelines, controversies related to T replacement therapy in older  men, and proposed future clinical directions.
authors.affiliation: Department of Biochemistry and Molecular Biology, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Barry R
authors.initials: BR
authors.lastname: Zirkin
authors.forename: Joyce Lisa
authors.initials: JL
authors.lastname: Tenover
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000818:Animals; D020249:Hormone Replacement Therapy; D006801:Humans; D007006:Hypogonadism / Q000188:drug therapy; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000097:blood / Q000502:physiology; D008297:Male; D008875:Middle Aged; D051381:Rats; D011914:Rats, Inbred BN; D013737:Testis / Q000187:drug effects / Q000502:physiology*; D013739:Testosterone / Q000096:biosynthesis / Q000097:blood* / Q000172:deficiency / Q000627:therapeutic use
chemical_list: D013739:Testosterone; D007986:Luteinizing Hormone