Diurnal rhythm in serum levels of inhibin B in normal men: relation to testicular steroids and gonadotropins.
Level 4 - case-series / case-control
Prospective single-group physiological observational study without a control or comparator arm.
PubMed 10323397 · doi:10.1210/jcem.84.5.5708
What was done
Thirteen healthy male volunteers (median age, 30 years) underwent continuous 24-hour blood sampling with measurements taken every 30 minutes. Serum samples were analyzed for inhibin B, FSH, LH, testosterone, estradiol, and sex hormone-binding globulin. Diurnal profiles, cross-correlations, and two-dimensional time-series analyses were conducted.
What was found
Inhibin B showed a significant diurnal variation, peaking in the early morning and reaching a nadir in the late afternoon, with an average decline of 3%/hour from 09:00 to 17:00. Significant cross-correlations were found between inhibin B and testosterone as well as estradiol, but not with FSH. Time-series analyses indicated a significant influence of testosterone on inhibin B, and mutual influence between estradiol and inhibin B. Absolute numerical concentrations were not provided in the abstract.
Why it matters
Demonstrates that serum inhibin B in healthy men follows a clear diurnal rhythm paralleling testicular steroids rather than FSH. This indicates that clinical and research assessments of inhibin B must account for time of day during sampling.
Limits
The study is limited by a small sample size (n = 13) restricted to healthy young men. The physiological observational design demonstrates temporal covariation but cannot establish direct causal mechanisms, and absolute hormone levels were not detailed in the abstract.
Cited by
- supports Testosterone secretion follows a diurnal rhythm with peak levels occurring early in the morning and trough levels at night.