PULSATILE SECRETION OF LH IN RELATION TO THE RESUMPTION OF OVARIAN ACTIVITY POST PARTUM

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Abstract
Changes in the pulsatile pattern of LH secretion in relation to the resumption of ovarian activity post partum have been studied in breast feeding mothers. Basal concentrations of LH were significantly lower than normal both when ovarian activity was completely suppressed and when there was evidence of some follicular development prior to the resumption of menstruation. Once menstruation resumed basal concentrations of LH were unchanged whether ovulation occurred or not. No difference in the frequency or amplitude of pulses in LH secretion could be found at any stage post partum in either breast or bottle feeding women. FSH levels remained constant throughout the post partum period while mean concentrations of prolactin fell as ovarian activity returned to normal. However, during the period of complete suppression of ovarian activity in breast feeding women, two patterns of pulsatile secretion of LH were observed. In 76% of observation periods, basal levels of LH were lower than normal and were characterized by low frequency and low amplitude pulses of LH. In contrast, in the remaining 24% of observation periods, basal levels and pulse amplitude and frequency of LH were similar to those in the follicular phase of normal menstrual cycles in these women. Individual women showed either or both of these patterns of secretion during the period of ovarian suppression post partum. The data suggests that the failure to maintain ovarian follicular development post partum in breast feeding women may be due to: (1) a direct block of LH action at ovarian level, perhaps by the high levels of prolactin associated with lactation and/or (2) an inability of the hypothalamic-pituitary axis—as a result of the suckling stimulus and/or prolactin—to maintain pulsatile secretion of LH in the face of the negative feedback effects of the increased oestrogen secretion resulting from the initiation of follicular development.