| Hormones
|
Roles
|
| Progesterone
|
- maintains pregnancy - initially synthesized by corpus luteum, then levels maintained by placenta
- hyperpolarizes myometrial cells (-65 mV), reduces excitability and conductivity
- Level in plasma may fall just before parturition, definitely decreases following delivery of placenta
|
| Estrogens
|
- Group of steroidal hormones, peak when parturition begins
- induce increased synthesis of actomyosin and ATP in myometrial cells
- alter membrane potential (-50 Mv) enhances excitation/conduction
- act to directly increase myometrial contraction
- indirectly by increasing oxytocin from pituitary gland
- Estriol - synthesized by fetus and placenta
|
| Oxytocin
|
- Peptide hormone (8aa) from maternal posterior pituitary, initiation and maintenance of labour (synthetic form labour induction)
- myometrium sensitivity to oxytocin (increased by estrogen, decreased by progesterone)
- stimulus for release - mechanical stimulation of uterus, cervix and vagina (ethanol inhibits release)
|
| Prostaglandins
|
- hydroxy fatty acids - sythesized by placenta, amniotic fliud contains mainly PGF2 alpha, causes myometrial contraction (also in maternal plasma)
- prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) - used to induce labour (intravenous, oral, intravaginal, intraamniotic)
- Aspirin inhibitor of PG synthesis - leads to increased duration of pregnancy
|
| Endocrine Development
|
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