Oxytocin is synthesised in hypothalamus and released from pituitary gland. It has a clear role in the initiation and propagation of labour. Due to the altered estrogen/progesterone ratio, the number of myometrial receptors for oxytocin will increase. This suggests that while oxytocin levels are unchanged, the contractile response to oxytocin increases due to increased receptor number.

Oxytocin binds to a Gq protein-coupled receptor on myometrial cell membrane. These receptors are coupled to Ca2+ channels. The intracellular Ca2+ levels will increase and so will the uterine contraction.

Oxytocin is drug of choice for the induction or propagation of labour. It is given intravenously by small amounts. The half-life is only 3 minutes, because the enzyme oxytocinase quickly degradates this nonapeptide. The adverse effects include anti-diuretic effects due to similarity with vasopressin, which can result in water intoxication and coma. Hypotension and tachycardia are other usual side effects.


Individual antiarrhythmic agents can alter the surface electrocardiogram. Characteristics of quinidine include: