PSYCHIATRY RESEARCH ELSEVIER Psychiatry Research 69 (1997) 1555162 Noradrenergic receptor sensitivity in obsessive-compulsive disorders: I. Growth hormone response to clonidine stimulation Francesca Brambilla”,” , Giampaolo Pernaa, Laura Bellodi”, Cinzia Arancio”, Angelo Bertani a, Giulia Perinib, Christian Carrarob, Franc0 Gavab “Dipartimento di Scienze Neuropsichiche lJniuersit& Istituto Scientifico H.S. Raffaele, Milano, Ital\ b Clinica Psichiattica lJniversit6 Padova, Ital\, Received 16 April 1996; revised 21 November 1996; accepted 16 December 1996 Abstract In 15 patients with obsessive-compulsive disorder COCD) and in 15 healthy controls postsynaptic a-2-adrenoceptor sensitivity was examined by measuring the growth hormone (GH) response to growth hormone-releasing hormone (GHRH) and to clonidine stimulation. Basal values of GH and somatomedin-C @MD-C) and mean GH responses to GHRH were the same in patients and controls, thus suggesting that a peripheral pathology of the somatotropic axis should not be present. GH responses to clonidine stimulation were blunted in patients suggesting that post-synaptic cY-2-adrenoceptors are subsensitive, possibly due to higher than normal noradrenergic secretion. 0 1997 Elsevier Science Ireland Ltd. Keywords: Obsessive-compulsive disorder; a-2-Adrenoceptors; Clonidine: Growth hormone-releasing hormone; Growth hormone 1. Introduction That alterations of the central noradrenergic (NE) system are involved in the pathogenesis of obsessive-compulsive disorder (OCD) has been * Corresponding author. Centro di Psiconeuroendocrinolo- gia, Istituto di Scienze Neuropsichiche, Istituto Scientific0 Ospedale S. Raffaele, Via Prinetti 27, Milan0 20127, Italy. Tel.: + 39 2 26433376; fax: +39 2 70122889. suggested on the basis of results obtained from studies in experimental animals and humans. In animals, increased central NE availability has been implicated in the mediation of compulsive- like repetitive behavior (Kokkinidis and Anisman, 1982). In humans, administration of clonidine (clan), an a-Zadrenoceptor agonist which in- hibits NE secretion presynaptically, improved the symptomatology in some OC patients (Knesevich, 1982; Hollander et al., 1988, 1991; Lee et al., 0165-1781/97/$17.00 0 1997 Elsevier Science Ireland Ltd. All rights reserved PrlSO165.1781(96)03032-l