Vasopressin receptors in islets enhance glucose tolerance, pancreatic beta-cell secretory function, proliferation and survival

Arginine vasopressin (AVP), a peptide secreted from the posterior pituitary, is chiefly regarded as a hormone involved in the regulation of body fluid balance and osmolality. However, recent evidence has revealed that posterior pituitary Hormones can exert important actions on endocrine pancreatic function. In the present study, the presence of AVP receptors, namely Avpr1a (V1a), Avpr1b (V1b) and Avpr2 (V2) was demonstrated in murine islets as well as rodent BRIN BD11 and human 1.1B4 beta-cells. Further to this, AVP was shown to induce significant concentration-dependent (10^-12 - 10^-6 M) increases of Insulin release from both rodent and human beta-cells, as well as mouse islets. Insulinotropic actions of AVP were completely annulled by specific V1a or V1b receptor antagonists, and partially abolished by an Oxytocin Receptor Antagonist. In addition, beta-cell Insulin secretory actions of AVP were augmented by both IBMX (200 μM) and KCl (30 mM) and linked to significantly increased cAMP production and [Ca²⁺]_i. AVP substantially increased proliferation of rodent and human beta-cells. Moreover, AVP fully protected against cytokine-induced beta-cell Apoptosis. AVP had no effect on glucagon secretion. Immunohistochemical examination of beta- and alpha-cells revealed co-expression of AVP with glucagon, and particularly Insulin. Finally, administration of AVP in combination with glucose to mice significantly reduced blood glucose, which was associated with increased plasma Insulin. These data indicate that AVP possesses novel and potentially important effects on pancreatic endocrine function. Understanding disturbances in islet AVP receptor signalling could reveal insight into the beta-cell defects associated with diabetes.