Absence of circadian rhythms of gonadotropin secretion in women.
Level 4 - case-series / case-control
Small physiological case series using a constant routine protocol without a comparative control group
PubMed 21346063 · doi:10.1210/jc.2010-2739
What was done
Eleven healthy, regularly cycling women aged 23 to 29 years were evaluated during the early follicular phase under a constant routine protocol in a clinical research center to control for sleep/wake, light/dark, activity, posture, and nutritional cues. Core body temperature was measured, and blood samples were collected to assay LH, FSH, glycoprotein free alpha-subunit (FAS), and TSH over 24 hours.
What was found
The abstract reports no exact numerical values. Core body temperature and TSH were best fit by a sinusoid model, confirming the presence of known circadian rhythms. In contrast, 24-hour profiles of LH, FSH, and FAS were best fit by a linear model, demonstrating an absence of circadian rhythmicity. Furthermore, LH and FAS pulse amplitudes and interpulse intervals showed no differences across evening, night, and morning.
Why it matters
These results indicate that previously reported diurnal fluctuations in gonadotropins are driven by environmental and behavioral cues rather than endogenous circadian regulation from the suprachiasmatic nucleus.
Limits
The sample size was small (11 participants), and measurements were limited to the early follicular phase, leaving other menstrual cycle phases unexamined. The abstract provides no exact numerical concentrations, pulse frequencies, or statistical test values.
Cited by
- contradicts Gonadotropins FSH and LH are released from the brain during the early morning hours.