title: Age or factors associated with aging attenuate testosterone's concentration-dependent enhancement of the regularity of luteinizing hormone secretion in healthy men.
abstract: BACKGROUND
  Healthy older men have reduced testosterone (Te) production and frequent, small irregular LH pulses. Which is cause and which is effect are not known.
  
  
  BACKGROUND
  In model systems, frequent and irregular LH pulses reflect attenuated feedback inhibition by Te.
  
  
  OBJECTIVE
  Factors associated with aging impair negative feedback by Te.
  
  
  METHODS
  Healthy men at an academic medical center were studied.
  
  
  METHODS
  The study used quantification of the regularity of LH release patterns during blockade of gonadal steroidogenesis and graded transdermal Te addback in 18 healthy men aged 18-65 yr.
  
  
  RESULTS
  In the cohort as a whole, stepwise Te repletion repressed LH concentrations (P = 0.001) and enhanced the quantifiable orderliness of LH release patterns (P < 0.001). By regression analysis, age attenuated the capability of increasing Te concentrations to regularize LH secretion patterns (P = 0.019). However, after a fixed GnRH stimulus, the effect of Te on LH regularity was invariant of the age factor (P = 0.16), thus pointing to a hypothalamic locus of impaired Te feedback.
  
  
  CONCLUSIONS
  Aging disrupts the capability of systemic Te concentrations to maintain orderly LH secretion under endogenous, but not exogenous, GnRH drive.
  
  
  CONCLUSIONS
  Age or factors associated with increased age reduce negative feedback by any given total Te concentration on hypothalamopituitary GnRH-LH outflow, thus contributing to disorderly LH secretion.
authors.affiliation: Endocrine Research Unit, Mayo Clinic School of Graduate Medical Education, General Clinical Research Center, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: Peter Y
authors.initials: PY
authors.lastname: Liu
authors.forename: Paul Y
authors.initials: PY
authors.lastname: Takahashi
authors.forename: Pamela D
authors.initials: PD
authors.lastname: Roebuck
authors.forename: Johannes D
authors.initials: JD
authors.lastname: Veldhuis
mesh_terms: D000328:Adult; D000375:Aging / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D025461:Feedback, Physiological; D006801:Humans; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D013739:Testosterone / Q000494:pharmacology*
chemical_list: D013739:Testosterone; D007986:Luteinizing Hormone