Milk synthesis and the prolactin brake on GnRH
End hormone or mediator · Casein Alpha-lactalbumin GnRH suppressed
Prolactin drives casein and alpha-lactalbumin synthesis to sustain lactation, and the same elevation suppresses hypothalamic GnRH pulses. That single fact explains both lactational amenorrhoea and the hypogonadism of any hyperprolactinaemia.
Traced from the start
- Tuberoinfundibular dopamine (prolactin-inhibiting factor)Thyrotrophin-releasing hormone (paraventricular nucleus)
- Supraoptic and paraventricular magnocellular neurones
- Lactotroph — prolactinPosterior pituitary — oxytocin release
- Mammary alveolus and myometrium
- Milk synthesis and the prolactin brake on GnRH
Detail
- Mechanism of the brake
- Prolactin inhibits kisspeptin neurones, slowing GnRH pulses and lowering LH and FSH
- Contraceptive effect
- Breastfeeding suppresses ovulation reliably only while the mother is amenorrhoeic, under six months postpartum and feeding exclusively
When it goes wrong
Prolactinoma in a man
Presents late with reduced libido, erectile dysfunction, gynaecomastia and mass effect such as headache and bitemporal hemianopia, rather than with galactorrhoea
Untreated hyperprolactinaemia in a woman
Amenorrhoea with an oestrogen-deficient state and accelerated bone loss; prolactin must be measured in any woman with amenorrhoea and a negative pregnancy test
Practise this structure
2 questions in the bank tagged Pituitary.
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