Unaltered oxytocin and vasopressin plasma levels in patients with schizophrenia after a 4-month daily treatment with intranasal oxytocin

The neuropeptide Oxytocin (OXT) has been proposed as a treatment for a number of neuropsychiatric disorders characterized by impaired social behavior, including schizophrenia. Although several studies reported chronic administration of OXT to be safe and tolerable, its effect on the circulating levels of OXT itself and of the related neuropeptide Arg-vasopressin (AVP) had not been assessed yet. Here, in a within-subjects crossover, double-blind, randomized controlled trial, we have assayed the plasma levels of OXT and AVP in 31 patients with schizophrenia treated daily for four months with 40 IU intranasal OXT or placebo. Our data indicate a baseline OXT concentration of 1.62 (SD 0.68) pg/mL, as determined by radioimmunoassay, that did not display any significant variation after chronic treatment with OXT or placebo. Similarly, the mean baseline AVP value of 2.40 (SD 1.26) pg/mL remained unchanged. In this study was also assessed cardiovascular and body fluids indicators (osmolality, plasma sodium concentration and systolic blood pressure), as well as a parameter for food intake (body mass index), that all remained stable. By reporting that a daily treatment with 40 IU intranasal OXT or placebo for 4 months does not impact on OXT and AVP plasma levels nor on cardiovascular, body fluids and food intake parameters, this study represents an important step towards developing OXT as a safe treatment.