Influence of suckling on gonadotropin secretion in the postpartum rhesus monkey

Kisspeptin and lactational anestrus: Current understanding and future prospects

Lactational anestrus, characterized by the suppression of pulsatile gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release, would be a strategic adaptation to ensure survival by avoiding pregnancy during lactation in mammals. In the present article, we first provide a current understanding of the central regulation of reproduction in mammals, i.e., a fundamental role of arcuate kisspeptin neurons in mammalian reproduction by driving GnRH/LH pulses. Second, we discuss the central mechanism inhibiting arcuate Kiss1 (encoding kisspeptin) expression and GnRH/LH pulses during lactation with a focus on suckling stimulus, negative energy balance due to milk production, and the role of circulating estrogen in rats. We also discuss upper regulators that control arcuate kisspeptin neurons in rats during the early and late lactation periods based on the findings obtained by a lactating rat model. Finally, we discuss potential reproductive technology for the improvement of reproductive performance in milking cows.

Bilateral oophorectomy in a pregnant woman: hormonal profile from late gestation to post-partum: Case report

BACKGROUND

A 16 week pregnant woman presented with massive theca-lutein cysts requiring bilateral oophorectomy. Pregnancy progressed uneventfully and spontaneous lactation ensued after delivery.

METHODS

To study the role of the ovary on the hormonal profile at the end of gestation and in post-partum, we measured FSH, estradiol (E2), unconjugated estrone (E1), unconjugated estriol (E3), sex hormone-binding globulin, progesterone, dehydroepiandrosterone sulphate and prolactin at 37 weeks gestation and at 8 h, 4 days, 5 weeks, and 2 months post-partum.

RESULTS

These hormones were within the range expected for ovary-intact pregnant and puerperal women until 4 days post-partum. At 5 weeks post-partum, FSH increased to a peri-menopausal range (31.4 IU/l) while estrogens remained within the normal puerperal range (E2=239 pmol/l; E1=102 pmol/l), contrasting with their rapid changes in non-pregnant women after bilateral oophorectomy. At 2 months, while partially breastfeeding, FSH, E2 and E1 were closer to menopausal range (68 IU/l, 136 and 70.2 pmol/l respectively), and hormone replacement was started.

CONCLUSIONS

We conclude that the ovary is not required to maintain a normal hormonal profile in late pregnancy and early puerperium. However, the increase in FSH to peri-menopausal levels at 5 weeks post-partum, despite breastfeeding, suggests that the ovary is needed to maintain low FSH concentrations during lactation.

On the mechanism of lactational anovulation in the rhesus monkey

The relative roles of infant suckling and of maternal prolactin (PRL) secretion in lactational anovulation were studied in ovary-intact and ovariectomized rhesus monkeys nursing young that had been removed from their natural mothers. Hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator activity was monitored electrophysiologically in freely behaving animals by radiotelemetry. Serum luteinizing hormone, PRL, estradiol, and progesterone were also measured. Suckling inhibited GnRH pulse generator activity and ovarian cyclicity in all ovary-intact females but had no such effect on the pulse generator in long-term ovariectomized animals. When PRL secretion was suppressed by daily bromocriptine administration, GnRH pulse generator activity remained significantly inhibited and ovulation was prevented in four monkeys (6 trials), whereas in two females (6 trials) a rapid increase in pulse generator frequency and the resumption of ovarian cyclicity were observed although suckling activity was maintained. One monkey displayed both response types. Although these results indicate that suckling per se is able to restrain GnRH pulse generator activity in the absence of PRL, they also suggest that the relative importance of these determinants is variable depending on factors that remain to be determined. The present study also confirms the permissive role of the ovary in the lactational suppression of GnRH pulse generator activity.

Nursing frequency, gonadal function, and birth spacing among !Kung hunter-gatherers

Mothers among !Kung hunter-gatherers nurse briefly and frequently, with brief intervals between nursing bouts (mean +/- standard error, 13.19 +/- 1.28 minutes). The low levels of 17 beta-estradiol and progesterone in the serum of the mother are correlated with infant's age and with interbout interval, but not with total nursing time. Maternal gonadal function is apparently suppressed by a timing-dependent, prolactin-mediated effect of breast stimulation. Interbout interval may be a key variable in lactation infertility. If so, it solves the puzzle of !Kung birth spacing.