Test-retest reliability of the prolactin and cortisol responses to D,L-fenfluramine challenge in disruptive behavior disorders.

We examined the intraindividual stability of plasma prolactin (PRL) and cortisol responses to D,L-fenfluramine challenges (1.0 mg/kg, p.o.), at a 1-week interval, in boys with disruptive behavior disorders. Two acute administrations of fenfluramine produced consistent and predictable effects on net prolactin responses (peak delta PRL, area under the curve delta PRL), but variable and unpredictable effects on net cortisol responses. The time course and magnitude of fenfluramine blood levels, not nor-fenfluramine, paralleled net PRL responses to fenfluramine. These data indicate that the PRL response to fenfluramine shows continuity within individuals over the course of 1 week, providing a reliable index to reflect the overall function of the serotonin system in the limbic-hypothalamus.