Mechanism of Action of Oxytocin Oxytocin binds to G-protein coupled receptors. In human myometrium these receptors couple to Gq and G11 receptors. This will activate Phospholipase -C hydrolysis and generate Inositol triphosphate (IP3) and Diacyl glycerol. These will mobilizes calcium ion from calcium deposits and also enhances voltage sensitive Ca2+ channels. This Ca2+ produces contraction. Oxytocin also increases local prostaglandin production and stimulates uterine contractions. Indications for Oxytocin 1. Induction of labour 2. Augmentation of labour 3. Reduction of postpartum bleeding 4. Induce abortion 5. Oxytocin challenge test Interactions for Oxytocin Sympathomimetics: Pressor effect of sympathomimetics may be increased leading to postpartum hypertension. Prostaglandins: Risk of uterine repture & cervical lacerations. Ergotamine: Synergistic effect in control of post partum haemorrhage.