Persistence of sleep-associated decrease in GnRH pulse frequency in the absence of gonadal steroids.

Abstract

There is dramatic slowing of GnRH pulse frequency during sleep in the early follicular phase of the menstrual cycle, but it is unknown whether this represents a primary effect of sleep or is dependent upon the sex steroid environment. Our objective was to determine 1) whether sleep affects GnRH pulse frequency in postmenopausal women (PMW) in whom gonadal hormones are low and 2) whether this relationship changes with aging. Studies were performed in the Clinical Research Center of an academic medical center. Subjects included healthy PMW, 45-55 (n = 8) and 70-80 (n = 6) years old. Subjects were studied during one night of polysomnographic-recorded sleep and one night of monitored wake during which blood was sampled every 5 min for 8 h. Pulsatile secretion of free α-subunit (FAS), a marker of GnRH secretion, was assessed. There were no differences in sleep macroarchitecture or sleep efficiency [75 ± 12% (mean ± sd)] between older and younger PMW. The FAS interpulse interval was longer during sleep than nighttime wake in all women (60.5 ± 4.3 vs. 52.0 ± 2.8 min, P = 0.03) with a similar effect in the two groups. FAS pulse amplitude did not differ between sleep and wake periods (474.8 ± 36.7 vs. 478.2 ± 36.5 ng/liter, P = 0.9). Sleep is associated with a significant decline in GnRH pulse frequency in both older and younger PMW. Its persistence in PMW reinforces the important connection between sleep and GnRH secretion.