Evidence for a dose-dependent effect in the sex-specific plasma prolactin response to naloxone in humans.

In attempt to ascertain if the sex specific plasma PRL response to naloxone, that we suggested in previous studies, was a dose dependent effect, 26 healthy volunteers were studied. They received naloxone 2 mg and 4.8 mg or a volume matched of saline i.v. as a bolus. Blood samples were collected and plasma PRL was measured by double antibody RIA. Naloxone, at dose of 2 mg, was able to decrease significantly plasma PRL levels in normally menstruating women (p less than 0.05 at 60 min.; p less than 0.01 at 120 min.), but not in post-menopausal ones and in men. In addition, the dose of 4.8 mg of the drug did not change plasma PRL in any group. These results suggest a dose-dependent effect in the sex specific PRL response to naloxone in humans.