V1b Vasopressin R/AVPR1B: ProductsAVPR1B acts as a receptor for arginine vasopressin. AVPR1B belongs to the subfamily of G protein-coupled receptors which includes AVPR1A, V2R and OXT receptors. Its activity is mediated by G proteins which stimulate a phosphatidylinositol-calcium second messenger system. AVPR1B is primarily located in the anterior pituitary, where it stimulates ACTH release. AVPR1B is expressed at high levels in ACTH-secreting pituitary adenomas as well as in bronchial carcinoids responsible for the ectopic ACTH syndrome.