Pulsatile Patterns of Gonadotropin Release in Subjects with and without Ovarian Function

Abstract

Minute-to-minute fluctuations of serum LH and FSH concentrations resembling a pulsatile pattern were demonstrated in both pre- and post-menopausal women. A pulsatile pattern of LH but not FSH was seen during the menstrual cycle. These appear to follow a varying frequency and magnitude according to the different phases of the cycle; a periodicity of 1–2 hr was seen during the early follicular phase, early luteal phase and midcycle surge while a periodicity of 4 hr was seen in the mid- and late-luteal phase. During the late follicular phase only “minor oscillations” were noted. A greater net increase of circulating LH was found in pulses during the midcycle surge which was more than double that seen during other phases of the cycle. In contrast, post-menopausal subjects had pulses of both gonadotropins. These were usually coincident, however, a minor asynchrony between LH and FSH patterns was discernible. The frequency of pulses in the postmenopausal subjects was the same as in the follicular phase and midcycle women while the average net increase per pulse of both LH and FSH was greater, approaching that seen during the midcycle surge which was more than double that seen during other phases of the cycle. In contrast, post-menopausal subjects had pulses of both gonadotropins. These were usually coincident, however, a minor asynchrony between LH and FSH patterns was discernible. The frequency of pulses in the postmenopausal subjects was the same as in the follicular phase and midcycle women while the average net increase per pulse of both LH and FSH was greater, approaching that seen during the midcycle surge. Thus, a variation in the magnitude of the pulsatile fluctuation accounted for elevations in “basal” levels during the mid-cycle surge and in post-menopausal women while a diminished frequency of pulses accompanied the lowering of “basal” LH levels during the luteal phase. Qualitative and uantitative differences in the pulsatile pattern observed between different phases of the cycle and between subjects with or without ovarian function provide evidence that ovarian steroids modulate the frequency and magnitude of the periodic release of gonadotropins by the pituitary gland.