Naltrexone effect on physiological and subjective response to a cold pressor task.

In this double-blind, cross-over study physiological (i.e. blood pressure, heart rate, plasma catecholamine concentrations, plasma cortisol concentrations) and subjective (i.e. McGill Pain Questionnaire, positive affect, distress) response to a cold pressor task was assessed in 19 subjects 1 h after the administration of 50 mg naltrexone and after placebo. Significant differences in plasma catecholamine concentrations were found. Plasma epinephrine concentrations increased during the 1 h period after naltrexone administration but remained largely unchanged after placebo administration. A significant treatment x period effect was also found for plasma norepinephrine concentrations. No significant differences were found for other measures assessed. Further research is necessary to determine the subpopulations in which these effects are of greatest magnitude and the long term safety implications of these effects.