Failure of naloxone to alter exercise-induced growth hormone and prolactin release in normal men

Growth hormone and prolactin levels during standardized exercise tests were measured in ten normal male volunteers, with and without previous intravenous administration of 4 mg naloxone. No significant influence of naloxone on hormone release could be observed. The lack of effect indicates that an opioid pathway is not involved in exercise-induced growth hormone and prolactin release in humans, in contrast to that in rats.