Absence of circadian rhythms of gonadotropin secretion in women

Abstract

Context: Diurnal rhythms of LH and FSH have been reported in normal women, but it is unclear whether these reflect underlying circadian control from the suprachiasmatic nucleus and/or external influences.

Objective: The aim of this study was to determine whether endogenous circadian rhythms of LH, FSH, and the glycoprotein free α-subunit (FAS) are present in reproductive-aged women.

Design and setting: Subjects were studied in the early follicular phase using a constant routine protocol in a Clinical Research Center at an academic medical center.

Subjects: Subjects were healthy, normal-cycling women aged 23-29 yr (n = 11).

Main outcome measures: Temperature data were collected, and blood samples were assayed for LH, FSH, FAS, and TSH.

Results: Core body temperature and TSH were best fit by a sinusoid model, indicating that known circadian rhythms were present in this population. However, the patterns of FSH, LH, and FAS over 24 h were best fit by a linear model. Furthermore, there were no differences in LH and FAS interpulse intervals or pulse amplitudes between evening, night, and morning.

Conclusions: Under conditions that control for sleep/wake, light/dark, activity, position, and nutritional cues, there is no circadian rhythm of LH, FSH, or FAS in women during the early follicular phase despite the presence of endogenous rhythms of TSH and core body temperature. These studies indicate that endogenous circadian control does not contribute to previously reported diurnal rhythms in reproductive-aged women and emphasizes the importance of environmental cues in controlling normal reproductive function.

Fig. 1.

Activity counts, temperature, LH, and FSH levels over 24 h in a subject studied during a 32-h constant routine. The gray shaded area represents the subject's habitual sleep time, during which she was kept awake. Note the circadian rhythm of temperature, but the lack of evidence of a circadian rhythm of LH or FSH. Inverted triangles mark statistically identified LH pulses.

Fig. 2.

Mean + sem of temperature, FSH, LH, FAS, and TSH levels (n = 11). The gray shaded area represents subjects' habitual sleep time, during which they were kept awake for the constant routine. Temperature and TSH are best fit with a sinusoidal model, whereas FSH, LH, and FAS are best fit with a linear model.

Fig. 3.

Interpulse intervals (upper panel) and pulse amplitudes (lower panel) of LH and FAS did not differ between evening, night, and morning during the constant routine studies.