IMPACT OF SLEEP ON THE CIRCADIAN EXCURSIONS IN THE PITUITARY GONADOTROPIN RESPONSIVENESS OF EARLY FOLLICULAR PHASE WOMEN

Whereas the nocturnal slowing of the LH pulse frequencies in the early follicular phase (EFP) of the menstrual cycle may be attributed to a sleep-associated increase in opioidergic activity, the concomitant augmentation of LH pulse amplitudes remains unexplained. We reasoned whether alterations in the pituitary gonadotropin responsiveness during the 24-hour rest-activity cycle may account for these enhanced LH pulse amplitudes during sleep. Accordingly, 12 EFP women (cycle days 3-5) were studied on 2 consecutive days during three occasions: at day time between 1000 and 1400 h (day studies), at night between 2200 and 0200 h, while the women were awake (night studies), and finally, during identical night hours, while the women were asleep (sleep studies). At all occasions, blood was collected at 10-min intervals for 4 h, while GnRH (25 mug) was administered twice within 2 h. During the day studies, prompt and sustained LH and FSH releases were noted in response to the first and second GnRH stimulations. However, the LH and FSH release after both the first and second GnRH challenges was markedly (P < 0.01) blunted during the night studies. By contrast, this decrease in LH, but not FSH response during the night was completely prevented, when GnRH was administered during sleep. Independent of the time at which GnRH had been administered, the second GnRH stimulations provoked much greater (P < 0.05 or less) LH and FSH releases then the first. Thus, a marked attenuation of the gonadotroph responsiveness is observed in EFP women during the night, and nocturnal sleep way eliminate this decline. Further, the priming actions on the gonadotrophs by repetitive GnRH stimulations are unaffected by the time of GnRH administrations. Collectively, these observations permit us to infer that the increased LH pulse amplitudes observed during sleep in EFP women may not be attributed to increased pituitary responsiveness.