Prolactin and cortisol responses to MK-212, a serotonin agonist, in obsessive-compulsive disorder.

To examine further the serotoninergic system in obsessive-compulsive disorder (OCD), the plasma concentrations of cortisol and prolactin and the behavioral responses after oral administration of MK-212 (6-chloro-2-[1-piperazinyl]-pyrazine), a serotonin agonist, and placebo were studied in 17 patients with OCD and nine normal controls. The two groups did not differ significantly in basal plasma prolactin or cortisol levels. Nevertheless, both the prolactin and cortisol response to oral administration of MK-212 (20 mg) were significantly blunted in the patients with OCD compared with those of the normal controls. MK-212 did not affect the intensity of OCD symptoms. However, MK-212, as compared with placebo, produced slight but statistically significant increases in self-ratings of nausea, dizziness, anxiety, feeling strange, and mixed feelings of calmness and restlessness, as well as depression and feeling high. These behavioral ratings were not significantly different in patients and normal controls. These findings are consistent with previous reports of diminished serotoninergic responsivity in OCD and raise the possibility of subsensitivity of at least some serotonin receptors in this disorder.