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To evaluate 5-hydroxytryptamine1A receptor responsivity in obsessive-compulsive disorder, we examined hypothermic, neuroendocrine, and behavioral responses to the selective 5-hydroxytryptamine1A receptor ligand ipsapirone in patients with primary obsessive-compulsive disorder and healthy controls. Twelve patients and 22 controls received a single dose of ipsapirone, 0.3 mg/kg, or placebo under double-blind, random assignment conditions. Ipsapirone induced hypothermia and release of corticotropin and cortisol but had no effect on behavior, including obsessive or compulsive symptoms. Thermoregulatory and neuroendocrine responses to ipsapirone were not consistently different between healthy controls and patients with obsessive-compulsive disorder. These results provide no direct support for the hypothesis that a serotonergic dysfunction related to 5-hydroxytryptamine1A receptors may be linked to the pathophysiologic characteristics of obsessive-compulsive disorder and point to the need for the evaluation of other 5-hydroxytryptamine receptor subtypes. Future studies of the responsivity of 5-hydroxytryptamine1A receptors to direct-acting ligands, such as ipsapirone, should facilitate assessment of the integrity of the 5-hydroxytryptamine system and its involvement in antiobsessional drug effects.

The selective 5-HT1A receptor ligand ipsapirone (IPS) induces corticotropin (ACTH) and cortisol secretion in humans. To explore 5-HT1A receptor-mediated hypothalamic-pituitary-adrenal (HPA) system activation in depression, 24 subjects (12 patients with unipolar depression and 12 individually matched controls) were given 0.3 mg/kg IPS or placebo in random order. Compared with controls, the depressed patients exhibited significantly decreased ACTH and cortisol responses to IPS in association with increased basal cortisol secretion. The impaired HPA response following 5-HT1A receptor challenge in unipolar depression could have resulted from glucocorticoid-dependent subsensitivity of the (post-synaptic) 5-HT1A receptor itself and/or from a defective postreceptor signaling pathway [inhibitory guanine nucleotide-binding protein (Gi)-adenylate cyclase complex function], thus supporting the hypothesis that a disintegrated 5-HT and HPA system interaction may be present in depression. Future studies of the HPA response to direct-acting 5-HT1A ligands, such as IPS, should facilitate the assessment of 5-HT/HPA system integrity in various affective disorders and its involvement in psychotropic drug effects.