The 24 h pattern of pulsatile luteinizing hormone, follicle stimulating hormone and prolactin release during the first 8 weeks of lactational amenorrhoea in breastfeeding women
Tay, C.C.; Glasier, A.F.; McNeilly, A.S.
Human Reproduction 7(7): 951-958
ISSN/ISBN: 0268-1161 PMID: 1430134 DOI: 10.1093/oxfordjournals.humrep.a137777
In women, breastfeeding results in a variable period of ovarian inactivity which is apparently related to suppression of the normal pulsatile release of luteinizing hormone (LH). However, pulse profiles had only been studied during the daytime. Since resumption of pulsatile LH secretion during puberty is initiated at high, the present study determined the pattern of pulsatile LH secretion in relation to that of follicle stimulating hormone (FSH) and prolactin, and suckling and ovarian activity at 4 and 8 weeks postpartum in 20 fully breastfeeding women with lactational amenorrhoea. Blood samples were withdrawn at 10 min intervals for 24 h from 0900 h to 0900 h at either 4 weeks (n = 9) or 8 weeks (n = 11) postpartum, while the mothers and babies continued their normal pattern of suckling activity. At 4 weeks postpartum, no LH pulses occurred over 24 h in six of the nine women while one (n = 1) or two (n = 2) LH pulses occurred in three of the nine women. In contrast, LH pulses were present in nine of the 11 women at 8 weeks postpartum. The pulse frequency varied considerably from two to eight pulses over the 24 h and there was no influence of the time of day or sleep on the time of the pulse release. Lactational amenorrhoea was maintained for at least 10 weeks afterwards and there was no relationship between the time of resumption of ovarian activity and the presence or absence of pulsatile LH secretion at 4 or 8 weeks postpartum. Plasma concentrations of FSH increased from 4 to 8 weeks postpartum and were higher in women with than in women without LH pulses. In two women, clear pulses of FSH with a half-life of .apprx. 72 min were observed coincident with LH pulses. There was no difference in the suckling pattern or plasma concentrations of prolactin in women in whom pulsatile LH was or was not observed suggesting that prolactin per se was not involved in the suppression of pulsatile LH release. Assuming that each pulse of LH represented a pulse of gonadotrophin releasing hormone (GnRH) released from the hypothalamus, the present study suggests that during the period of total ovarian inactivity, suckling disrupts, but does not totally inhibit, the normal pattern of pulsatile GnRH release and hence release of LH and FSH from the pituitary. Thus, suckling maintains ovarian activity during lactational amenorrhoea by causing an abnormal pattern of gonadotrophin release that is insufficient to drive follicle development.