Plasma adrenocorticotropin responses to opioid blockade with naloxone: generating a dose–response curve in a single session

We examined two methods of generating a dose–response curve to the opioid receptor antagonist naloxone. In 15 healthy male subjects (18–25 years) plasma adrenocorticotropin (ACTH) responses to five doses of naloxone studied over 5 separate days were compared to plasma ACTH responses to five incremental doses of naloxone studied within a single session. There was a statistically significant positive correlation in ACTH responses (area under the curve and peak) between dosing methods. Furthermore, the doses of naloxone that produced half-maximal and maximal ACTH response were similar. The comparability of ACTH responses between the two naloxone dosing techniques, combined with the safety and ease associated with the single-session methodology, underscores the usefulness of the single-session technique for future investigations.