WHAT  IS OXYTOCIN’S BIOLOGICAL  FUNCTION?

Oxytocin  is a hormone synthesized in brain regions such as the supraoptic nucleus and  paraventricular nucleus of the hypothalamus, which are critical for behavioral  and physiological homeostasis. In the popular imagination, this hormone is  probably best known for its involvement in the control of social, sexual, and  romantic attachment and behavior. By studying animal models, neurobiologists  have shown the possible involvement of oxytocin in pair-bonding, along with  other hormones like arginine-vasopressin and dopamine. Several studies involving  the administration of oxytocin in humans have also implicated a role for this  hormone in forming and maintaining human romantic relationships.

Oxytocin  also functions as a reproductive health regulator, stimulating uterine smooth  muscle and serving as one of the most potent uterotonic agents. It also impacts  reproduction-related functions for both women and men such as influencing  estrous cycle length, promoting follicle luteinization in the ovary and ovarian  steroidogenesis, and stimulating erections and ejaculation.

Most  recently, emerging evidence shows that oxytocin helps regulate the body’s response to stress, and that it is  particularly involved in regulating the hypothalamo-pituitary-adrenal axis and  cardiovascular function.

IN  WHAT CLINICAL SCENARIOS COULD OXYTOCIN TESTING BE USED?

Although  oxytocin testing has not yet become a routine clinical assay, in the future it  could aid healthcare providers in assessing behavioral, psychiatric, and  stress-related conditions. Specifically, this could include the work-up of mood  disorders, anxiety disorders, obsessive-compulsive disorder, and the evaluation  of burnout.

How  is oxytocin measured?

Immunoassays  are the most common method for determining oxytocin concentrations. The first  oxytocin assays were based on the radio-immunoassay format, but now most are  enzyme-linked immunosorbent assays (ELISAs). These ELISA-based tests have  acceptable limits of quantification of approximately a few pg/mL and  imprecisions usually below 10%.

However,  they aren’t standardized, and  there is clear heterogeneity/lack of commutability between results obtained  using different oxytocin immunoassays. This could be related to the specificity  of the antibodies used in these assays and also to cross-reacting components,  which reinforces the need for a sample’s extraction before testing. Sample extraction has a significant  impact on oxytocin results: The concentrations of oxytocin measured by enzyme  immunoassay without plasma extraction are more than 100-fold higher than in  extracted plasma.

To  improve the specificity of oxytocin measurements, assays based on liquid  chromatography-tandem mass spectrometry (LC-MS/MS) have now been validated for  this hormone. Some of these two-dimensional LC-MS/MS assays are ultra-sensitive,  with lower limits of quantification close to 1.00 pg/mL and with imprecisions  also lower than 10%.

WHAT  SAMPLE TYPES ARE USED FOR OXYTOCIN TESTING?

Oxytocin  can be detected in various physiological fluids such as plasma, serum, saliva,  urine, and cerebrospinal fluid. However, as oxytocin assays evolve, saliva could  ultimately become the sample of choice because it is less invasive and would  also facilitate data comparison due to the fact that a large number of studies  are already using this matrix to measure oxytocin.