Ultradian and circadian patterns in luteinizing hormone secretion during reproductive life in women

Based on the findings of close links between intermittent hypothalamic releasing hormone stimulation and hypophyseal gonadotrophin response, an assessment of the pulsatility of serum gonadotrophins may represent a feasible way to indirectly evaluate central regulatory processes in humans. Since ovarian steroid feedback is virtually absent in hypogonadal women, their luteinizing hormone (LH) pulsatility may represent the unrestrained LH pulse rhythm at its maximal rate. Relative changes in the LH pulse characteristics during the menstrual cycle could then be referred to this basic pulsatility. Hence, LH pulse frequencies increase during cycle periods of high sex steroid exposure, but this increase is limited to the LH periodicities found in hypogonadal women. Furthermore, LH pulse amplitudes are successively enhanced from the follicular to the luteal phase of the cycle yet they never exceed those found in hypogonadal subjects. In addition, circadian excursions subserve pulsatile LH secretion during all periods of the menstrual cycle, although the character of these circadian rhythmicities differs from that observed in the LH secretory profiles of hypogonadal women. Thus, albeit profoundly modulated by ovarian sex steroid feedback during the menstrual cycle, LH pulsatility and its circadian variations in women during the menstrual cycle is confined to the ultradian and circadian LH secretory patterns of the hypogonadal state.