. Attenuated stressinduced catecholamine release in mice lacking the vasopressin V1b receptor. Am J Physiol Endocrinol Metab 291: E147-E151, 2006. First published February 7, 2006 doi:10.1152/ajpendo.00005.2006.-Vasopressin V1b receptor is specifically expressed in the pituitary and mediates adrenocorticotropin release, thereby regulating stress responses via its corticotropin releasing factor-like action. In the present study we examined catecholamine release in response to two types of stress in mice lacking the V1b receptor gene (V1bR Ϫ/Ϫ mice) vs. wild-type mice. There were no significant differences in the basal plasma levels of catecholamines between the two genotypes. In response to stress induced by forced swimming, norepinephrine (NE), but not epinephrine (E) or dopamine (DA), was increased in wild-type mice, whereas the increases in NE and DA were not observed in V1bR Ϫ/Ϫ mice. In wild-type mice, E, but not NE or DA, was increased in response to social isolation stress, whereas the increase in E was not observed in V1bR Ϫ/Ϫ mice. These results suggest that the V1b receptor regulates stress-induced catecholamine release. Because it has been suggested that arginine-vasopressin (AVP) is related to the development of depression, we also evaluated immobility time in the forced swimming test, and we found no significant change in V1bR Ϫ/Ϫ mice. Taken together, these findings suggest that, in addition to the previously elucidated effect on the hypothalamic-pituitary-adrenal axis, vasopressin activity via V1b receptors regulates stress-induced catecholamine release.V1b receptor knockout mice; norepinephrine; epinephrine; dopamine; immobility time in the forced swimming test ARGININE VASOPRESSIN (AVP) has diverse physiological functions, and these physiological effects are mediated through the binding of AVP to specific receptor subtypes of the target cells. AVP receptors are G protein coupled and are divided into at least three types (V 1a , V 1b , and V 2 ). The V 1a (vascular/hepatic) and V 1b (anterior pituitary) receptors act via phosphatidylinositol hydrolysis and Ca 2ϩ mobilization (9). The V 1a receptor mediates physiological effects such as smooth muscle cell contraction and proliferation, platelet aggregation, and glycogenolysis. The V 1b receptor exists in the anterior pituitary, where it stimulates corticotropin release. The V 2 receptor is found primarily in the kidney and mediates the antidiuretic effect of AVP via adenylate cyclase/cyclic AMP signals (20) and aquaporin 2 trafficking (15). All of these receptors have been cloned (11,12,13) and belong to the family of seven membrane-spanning G protein-coupled receptors.AVP is synthesized primarily in the magnocellular neurons of the hypothalamic paraventricular nuclei (PVN) and in the supraoptic nuclei that project to the posterior pituitary. In addition, parvocellular neurons of the PVN coexpressing AVP and corticotropin-releasing hormone (CRH) coordinate hypothalamic-pituitary-adrenal (HPA) system activity and project to the external layer of th...