Arginine Vasopressin and Oxytocin Effects in Mouse Pancreatic β-cells: Receptors Involved in Stimulation of Insulin Release

Recently AVP and OT were suggested to increase insulin release by stimulating phosphoinositide metabolism in pancreatic β-cells. In this study, mouse islets were used to identify the receptors involved in the effects of AVP and OT. Both agents caused concentration-dependent (0.1 nM to 10 microM) increases in insulin release and IP levels. The potencies of AVP and OT were similar, and their maximal effects were not additive. Synthetic agonists selective for AVP (V₁) and OT receptors in other tissues were equipotent with the natural agonists on insulin release and almost equipotent on IPs. Antagonists selective for V₁ and OT receptors inhibited both types of effects with a potency that varied with the nature of the agonist. Both AVP and OT were ∼10-fold potent on insulin release (EC₅₀ ≈2 nM) than on IPs (EC₅₀ ≈25 nM). Moreover, the antagonists more readily inhibited the effects of all agonists on IPs than on insulin release. Pancreatic β-cells may possess either a single type of receptor that is distinct from classic V₁ or OT receptors, but is closer to the latter, or both V₁ and OT receptors coupled to common effectors. The acceleration of phosphoinositide turnover might not be the sole mechanism involved in the stimulation of insulin release by AVP and OT.