Aging in healthy men impairs recombinant human luteinizing hormone (LH)-stimulated testosterone secretion monitored under a two-day intravenous pulsatile LH clamp.
BACKGROUND
Testosterone (Te) depletion in aging men in principle could reflect deficits in the hypothalamus, pituitary gland, or testis. Available pharmacological studies of possible failure of Leydig cell steroidogenesis remain inconclusive.


OBJECTIVE
The objective of the study was to assess Te secretion in older and young men in response to near physiological LH stimulation.


METHODS
Pulsatile i.v. infusion of recombinant human LH was administered for 2 d to stimulate Te secretion during suppression of endogenous LH concentrations with a potent selective GnRH receptor antagonist (ganirelix). SUBJECTS/CONTEXT: Healthy older (aged 60-73 yr, n = 8) and young (19-30 yr, n = 13) men were studied in an academic setting.


METHODS
Pulsatile LH and Te concentrations on the second day of exogenous LH stimulation were measured.


RESULTS
Serum ganirelix concentrations and infused LH pulse increments were similar by age. In contrast, older subjects manifested: 1) reduced mean Te concentrations (P = 0.016), Te peak heights (P = 0.014), increments (P = 0.010), summed areas (P < 0.013), and interpeak Te concentrations (P = 0.023); 2) decreased Te to LH concentration ratios (P = 0.002); 3) diminished LH-Te feed-forward synchrony (P = 0.020); and 4) a blunted amplitude (P = 0.036) and advanced phase (P = 0.013) of diurnal Te rhythms.


CONCLUSIONS
A novel regimen of pulsatile LH stimulation for 48 h during GnRH receptor blockade unmasks deficits in pulsatile, basal, synchronous, and nyctohemeral Te secretion in healthy older men. These findings do not exclude concomitant defects in GnRH outflow and/or Te-negative feedback in the aging male.
Liu
Peter Y
PY
Endocrine Research Unit, Department of Internal Medicine, Mayo School of Graduate Medical Education, General Clinical Research Center, Mayo Clinic, Rochester, Minnesota 55905, USA.
Takahashi
Paul Y
PY
Roebuck
Pamela D
PD
Iranmanesh
Ali
A
Veldhuis
Johannes D
JD
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D019277:Entropy; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D007262:Infusions, Intravenous; D007985:Leydig Cells / Q000187:drug effects / Q000378:metabolism; D007986:Luteinizing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D011966:Receptors, LHRH / Q000037:antagonists & inhibitors; D011994:Recombinant Proteins / Q000494:pharmacology; D012044:Regression Analysis; D013268:Stimulation, Chemical; D013737:Testis / Q000187:drug effects / Q000378:metabolism; D013739:Testosterone / Q000378:metabolism*
D006727:Hormone Antagonists; D011966:Receptors, LHRH; D011994:Recombinant Proteins; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; C061018:ganirelix