Testosterone-Driven Growth-Hormone (GH) Secretion in Aging Men

Repletion of testosterone in older men drives pulsatile GH secretion via conjoint facilitation of feedforward by the primary secretagogues GHRH and GHRP and repression of feedback by the dominant inhibitor, somatostatin; and, in corollary, testosterone acts via aromatization to estradiol and/or reduction to 5 alpha-dihydrotestosterone

Inclusion criteria

• healthy men between the ages of 50 and 80;
• normal weight (within 30% of ideal body weight defined by New York Metropolitan Life tables); and
• normal hematocrit (greater than 38%);
• community dwelling; and
• voluntarily consenting

Exclusion criteria

• recent use of psychotropic or neuroactive drugs (within five biological half-live);
• obesity (outside weight range above);
• anemia (hematocrit < 38%);
• drug or alcohol abuse, psychosis, depression, mania or severe anxiety;
• acute or chronic organ-system disease;
• endocrinopathy, other than primary thyroidal failure receiving replacement;
• nightshift work or recent transmeridian travel (exceeding 3 time zones within 7 days of admission);
• acute weight change (loss or gain of > 2 kg in 6 weeks);
• allergy to administered compounds; and
• unwillingness to provide written informed consent.