oxytocin

Introduction

oxytocin is a nine amino acid peptide natural hormone secreted by the posterior pituitary gland via positive feedback mechanisms such as touch, nipple stimulation and in labour
it is made in magnocellular neurosecretory cells of the supraoptic and paraventricular nuclei of the hypothalamus and is stored in Herring bodies at the axon terminals in the posterior pituitary.
it is also produced by some neurons in the paraventricular nucleus that project to other parts of the brain and to the spinal cord
oxytocin-containing cells have also been identified in several diverse tissues outside of the CNS
it was discovered in 1906, and in 1953, was the first ever polypeptide hormone to be sequenced and synthesized
it is the preferred uterotonic agent for use to augment labour and for activeED Mx of 3rd stage of labour
virtually all vertebrates have an oxytocin-like nonapeptide hormone that supports reproductive functions and a vasopressin-like nonapeptide hormone involved in water regulation. These genes appear to have arisen from a duplication event with the ancestral gene being some 500 million years old

acts upon oxytocin receptors on cells (and on vasopressin V1a receptors)
oestrogen increases the secretion of oxytocin and to increase the expression of its receptor, the oxytocin receptor, in the brain
testosterone may suppress oxytocin secretion to allow hunting and aggressive behaviours
uterotonic
may reduce fetal brain activity during labour and perhaps reduce hypoxic damage
let down of milk in lactation in response to nipple stimulation by the baby
regression of the corpus luteum
pair bonding, attachment, altruism and social relationships
may play a role in recognition, sexual arousal, erections, orgasms, trust, reducing anxiety, reducing stress, enabling sleep, and in reducing cravings in addiction¹⁾
role in triggering group defensive behaviours
role in formation of emotional memories
role in sperm movement, contracting ejaculatory tissues (via vasopressin V1a receptors), and production of testosterone in men
may also have roles in bone formation, glycaemia, male sexuality, cardiac differentiation, and nonregulated cellular proliferation
may reduce inflammation and increase wound healing
high levels may have a role in development of benign prostatic hyperplasia (BPH)
low levels may have a role in depression

pregnancy except in labour and in ED Mx of 3rd stage of labour
hypersensitivity to oxytocin
during labour if patient should be considered for a LUSCS instead
- cephalopelvic disproportion
- fetal distress
- PH LUSCS
- etc.

painful uterine contractions
when given in labour, it may cause:
- fetal distress
- uterine rupture (rare)
- retinal haemorrhage in newborns
- increased neonatal jaundice
high doses can cause:
- increased renal excretion of sodium (it is similar to argipressin (vasopressin / ADH)) and cause hyponatraemia which may cause restlessness, drowsiness, confusion, slurred speech or seizures
most other adverse effects are minor or rare

¹⁾