Salivary Oxytocin

Background

Oxytocin (H-Cys(1)-Tyr-Ile-Gln-Asn-Cys(1)-Pro-Leu-Gly-NH2), a neurohypophysial peptide hormone, consists of nine amino acids linked with a [1-6] disulfide bond and a semi-flexible carboxyamidated tail. In humans, oxytocin is primarily synthesized in the hypothalamus and secreted into the bloodstream by the posterior pituitary gland. Oxytocin is released through a positive feedback mechanism where secretion of the hormone stimulates more of its own release. Previous research using plasma and serum has determined that oxytocin exists both as a cyclic active molecule and, through disulfide exchange, complexed with other disulfide containing proteins (1). Frequently called the “love and bonding hormone,” oxytocin is most known for its role in sexual reproduction and mother-infant interactions such as breastfeeding (2). In both sexes, oxytocin is released during romantic behaviors such as hugging, kissing, and sexual activity. In the female body, oxytocin is implicated in advancing uterine contractions and ‘milk letdown’ during lactation. During labor, oxytocin stimulates the uterine muscles, which further intensifies the contractions. Once the baby is born, this analyte promotes lactation by increasing movement of milk from the breast alveoli to the nipple, signaling its release during breastfeeding. In men, oxytocin has a role in moving sperm as well as well as in regulating testosterone production. Research suggests that oxytocin functions as a neurotransmitter, plays a role in determining social behavior (3,4), and is a crucial part of both male and female reproductive physiology, while it is also potentially involved in neuropsychiatric disorders such as anxiety and schizophrenia (5). Many mental illnesses, social/relationship issues, and atypical parenting behaviors have been correlated to abnormal oxytocin levels (6). Low levels of this analyte have been linked to autistic spectrum disorders, depression, and addiction (7,8). People with higher levels of oxytocin typically have fewer depressive symptoms and have stronger social ties than those with lower oxytocin levels. However, elevated oxytocin levels can also intensify past memories, which may induce heightened feelings of stress and social anxiety (9,10). Men with elevated levels of oxytocin may develop benign prostatic hyperplasia, which often causes urinary complications. In summary, oxytocin is part of a complex psychological and biological system which reinforces many of the typical human emotions and guides social interactions.