Oxytocin analysis from human serum, urine, and saliva by orbitrap liquid chromatography-mass spectrometry.

Abstract

Oxytocin (OT) is a neurohormone that has gained interest recently due to its emerging role in cognition and social/emotional behaviors, including possibly depression and autism. OT is commonly measured using enzyme- or radio-based immunoassays (RIA, ELISA), which lack specificity or are complicated to perform and involve hazardous radioactive material. We have developed a high resolution accurate-mass (HRAM) liquid chromatography-mass spectrometry (LC-MS) method that separates interferences and selectively and accurately quantitates native OT from human serum, urine, and saliva after solid phase extraction. The doubly protonated OT ion m/z 562.25503 was selected for quantitation due its high signal intensity. With our method lower limit of detection (LLOD) of 5-25pg/mL, we measured native OT in serum from pregnant women (16-24pg/mL) and rats (350pg/mL), and in serum, urine, and saliva from a healthy male after intranasal (IN) OT application of 100IU and 20IU and from a healthy post-menopausal female after IN OT application of 100IU. Peak levels were detected in serum, urine, and saliva 15-30minutes after each dose then decreased to below detection limits 1-2hours thereafter. We were unable to detect native OT in serum from non-pregnant/non-lactating/non-medicated women due to levels known to occur below 5pg/mL. The fast elimination of OT we found is in excellent agreement with the pharmacokinetics of OT in other studies. The effects on the central nervous system occurring after IN OT administration remains to be determined.