Endocrinology of Parturition

Question 1

What are the three stages of parturition?

Answer 1

Initiation of myometrial contractions
Expulsion of the fetus
Expulsion of the fetal membranes

Question 2

What are the three foetal hormones responsible for maturing the fetus?

Answer 2

Glucocorticoids, fetal cortisol, fetal stress

Question 3

What is the effect of the glucocorticoids?

Answer 3

Raise blood glucose levels

Question 4

What is veratrum calcifornicum?

Answer 4

Cyclopic lamb that has a delayed labour, absence of hypophyseal stalk and pituitary, adrenal hypoplasia, insufficiency as far as steroid production and metabolism is concerned & a prolonged gestation

Question 5

What does fetal cortisol do?

Answer 5

Reduces progesterone levels (removes block on myometrial contractions, reproductive tract secretions increase) & stimulates uterine prostaglandin production (causes uterine contraction, lysis of the corpus luteum, relaxin production)

Question 6

What drugs can be given before labour?

Answer 6

Dexamethasone – matures the fetus

Question 7

What drugs can be given during/after labour?

Answer 7

Oxytocin – strengthens contractions
Atosiban – reduces contractions (oxytocin receptor antagonist)
Estrumate – strengthens contractions (PGF2α agonist)

Question 8

What drugs can be given during labour?

Answer 8

Clenbuterol – inhibit contractions and cause relaxation (β2 adrenergic agonist)

Question 9

Why might you want to speed up labour?

Answer 9

Uterine inertia or haemorrhage, remove abnormal uterine product, retained placenta

Question 10

What are the effects of stretch?

Answer 10

Increases oxytocin receptors & COX-2 which increases PGE & PGF2α

Question 11

What are they key second messenger and enzyme involved in myometrial contractions?

Answer 11

Ca2+ is critical second messenger, myosin light chain kinase is a key regulatory enzyme

Question 12

How does myometrial contraction come about?

Answer 12

Calcium enters the cell and binds to calmodulin, activates MLCK which phosphorylates MLC, enables actin-myosin cross bridge to form (no troponin complex in smooth muscle)

Question 13

What are the two mechanisms for keeping normally calcium levels low?

Answer 13

Ca2+ ATPase and the sodium-calcium exchanger

Question 14

What is the purpose of the gap junctions?

Answer 14

Low resistance pathways between individual myometrial cells that allow the uterus to act as an electrical syncytium

Question 15

What is the neuro-hormonal reflex?

Answer 15

Increasing pressure on the cervix activates pressure sensitive neurons, relay afferent information to the hypothalamus (PVN), neural input to the posterior pituitary stimulates oxytocin release

Question 16

What hormonal and neural inputs are responsible for increasing myometrial contractions?

Answer 16

Oxytocin, PGF2α, ANS via pelvic plexus through α1 receptors