Questions on Female Hormone Stimulation & Inhibition

[garytse86]

Just a few questions on female hormones:

1) When an egg is fertilised, Human Chorionic Gonadotrophin (HCG) is released by the placental trophoplast, but what exactly is the stimulation for the secretion? (e.g. secretion of oestrogen is stimulated by LH and FSH)

2) Similarly, which hormones stimulate the secretion of oxytocin and prolactin?

3) What inhibits the production of oxytocin and prolactin?

Thanks so much, I can't seem to find anything on inhibition of hormones...

Gary

 

[Moonbear]

First, the placenta is composed of cells from the fetus, not the mother, so doesn't rely on stimulation of other maternal hormones to know what to do, it just starts producing hCG as soon as it is formed. The hCG is then what signals the mother's endocrine system that pregnancy has occurred and to adjust hormonal events to sustain that pregnancy.

Prolactin is produced in and released from the anterior pituitary. Prolactin is primarily regulated by the brain neurotransmitter dopamine. It is also believed there is another Prolactin Inhibiting Factor. This is because prolactin is unusual in the way the pituitary responds if signals from the brain are blocked. Most pituitary hormones are regulated by "releasing factors" produced in the brain, and when you remove those signals, the pituitary hormones stop being secreted. In contrast, if you block signals from the brain to the pituitary, prolactin secretion increases, suggesting there is an inhibiting factor released by the brain to the pituitary to tell prolactin when to shut off rather than when to turn on. To my knowledge, no such factor has yet been identified. Don't be confused if you read through the literature. There is something with the name Prolactin Inhibiting Factor (PIF) that has nothing to do with prolactin...when it was initially discovered, the investigators thought it was regulating prolactin and named it based on that, then found out they were wrong and it's stuck with an inappropriate name.

Oxytocin is produced in neurons in the brain (hypothalamus) and stored in the posterior pituitary for release. As such, oxytocin is under direct neuronal control more so than from feedback of other hormones.

Hope that helps.

 

[garytse86]

thanks moonbear, that was very very useful :)

so there is no hormonal stimulus for the secretion of prolactin? So how does the baby sucking for milk forces the anterior pituitary gland to secret prolactin?

 

[Moonbear]

Suckling doesn't really trigger prolactin release, it stimulates oxytocin release (for milk let-down) via the nervous system. Prolactin is released in high concentrations throughout lactation, primarily because estrogens are very low during this time. Estrogens, via dopamine, inhibit prolactin release, so when estrogens are low prolactin is high. Prolactin is required for milk production, so is released all the time during lactation, whereas oxytocin is needed to release the milk so, so is triggered by stimuli from the baby.

 

[garytse86]

thats what my book says (note its from Edexcel so...)

Prolactin stimulates the secretion of milk by the cells in the mammary glands. Oxytocin stimulates contration of muscle cells that allow the milk to pass into ducts leading to the nipples. When the baby sucks, this stimulates the production of prolactin, so that the supply of milk matches demand.



Please help... but thank you very much Moonbear you have helped me a lot