Vasopressin V1b receptor (also called V3R) is a G protein-coupled receptor (GPCR) of the G_q type, thus activating the phospholipase C signaling pathway upon activation. It is part of a family of GPCRs triggered by vasopressin that further include V1R, V2R, oxytocin receptors and purinergic receptors. While V1R and V3R are G_q GPCRs, V2R is coupled to the G_s protein and activates adenylate cyclase^1,2.

The V1b receptor has an intracellular C-terminal, seven transmembrane domains, and an extracellular N-tail; the transmembrane and extracellular domains are responsible for interacting with agonists and to signal for activation of the coupled G_q receptor^1,2.

The V1b receptor is mainly detected in the corticotrophs of the anterior pituitary gland in the brain where it regulates the release of adrenocorticotrophic hormone (ACTH) upon stimulation of vasopressin-corticotrophin-releasing hormone conjugates².
V1b KO mice show that the receptor is critical for the functionality of the hypothalamic-pituitary-adrenal axis, and demonstrate its importance in regulating glucose levels. Recent studies have also suggested that lactating rats treated with V1b antagonists, were less nurturing and similarly aggressive compared with untreated rats and that mice with reduced expression of V1b and V1a receptors have shown resistance to jet-lag^1,3,4.