A diurnal variation in testicular hormone production is maintained following gonadotrophin suppression in normal men.
Level 3 - non-randomized controlled study
Controlled clinical physiological trial with parallel control group (randomization not specified)
PubMed 17201811 · doi:10.1111/j.1365-2265.2006.02696.x
What was done
Twenty healthy men were evaluated in a clinical research center: 10 untreated controls and 10 men receiving testosterone combined with etonogestrel to suppress gonadotrophin secretion. Blood was sampled hourly over 24 hours to measure serum testosterone, inhibin B, LH, FSH, and cortisol. Urinary excretion of testosterone and epitestosterone was also measured.
What was found
The abstract reports no absolute numbers, effect sizes, or p-values. Controls demonstrated diurnal variation in serum testosterone and LH, but not FSH. The treated group had similar testosterone levels but lacked diurnal testosterone variation. Inhibin B periodicity was found in 5 of 10 controls and 9 of 10 treated men. Both groups showed diurnal variation in cortisol. Urinary testosterone showed no diurnal variation in either group, whereas urinary epitestosterone showed a morning peak in both groups despite markedly lower overall excretion in treated men.
Why it matters
This study clarifies that diurnal serum testosterone variation in men is driven by LH pulsatility and secretion rather than changing clearance rates, while demonstrating that intrinsic, gonadotrophin-independent rhythms exist for Sertoli cell function (inhibin B) and testicular steroidogenesis (epitestosterone).
Limits
The sample size is very small (n = 20 total, 10 per group), and the abstract does not state whether treatment allocation was randomized. No numerical measurements, variance estimates, or statistical significance thresholds are reported in the abstract.
Cited by
- supports Testosterone is produced nocturnally and peaks in the morning.