Plasma oxytocin in response to pharmaco-challenge to D-fenfluramine and placebo in healthy men.

The neuropeptide oxytocin is produced in the hypothalamus and released centrally and peripherally in response to serotonergic stimulation. Plasma oxytocin levels may be a candidate as a biological index of serotonergic function in response to pharmacological challenge by serotonergic agents. Fourteen male healthy subjects underwent a placebo challenge and a D-fenfluramine (D-FEN) (0.5 mg/kg) challenge on different days. Serial plasma oxytocin and prolactin levels were measured on each challenge day. D-FEN was associated with an increase in both oxytocin and prolactin. Plasma oxytocin may function as an index of central serotonin (5-HT) function in human subjects. Since oxytocin is released directly from limbic-hypothalamic cells, this response presumably represents a direct central assessment of 5-HT response in limbic-hypothalamus. Further work will determine if the oxytocin response to 5-HT pharmaco-challenge, by virtue of its central origin, is more highly related to measures of psychopathology (e.g. aggression) than that of less central outcome parameters of 5-HT responsiveness (e.g. prolactin).