Vasopressin stimulates insulin release from islet cells through V1b receptors: a combined pharmacological/knockout approach.

Vasopressin receptor subtype(s) responsible for stimulation of insulin release from pancreatic beta cells were investigated by using subtype-selective antagonists and mice that were genetically lacking either V1a or V1b receptors. Arginine vasopressin (AVP) increased insulin release from isolated mouse islet cells in a concentration-dependent manner, with a submaximal response at 100 nM. Reverse transcription-polymerase chain reaction (RT-PCR) analysis detected V1b and oxytocin, but not V1a or V2, receptor transcripts in mouse islet cells. We characterized the recently synthesized vasopressin receptor subtype antagonists (2S)1-[(2R 3S)-(5-chloro-3-(2-chlorophenyl)-1-(3,4-dimethoxybenzene-sulfonyl)-3-hydroxy-2,3-difydro-1H-indole-2-carbonyl)-pyrrolidine-2-carboxamide] (SR49059), 1-[1-[4-(3-acetylaminopropoxy)benzoyl]-4-piperidyl]-3,4-dihydro-2(1H)-quinolinone (OPC-21268), and (2S,4R)-1-[5-chloro-1-[(2,4-dimethoxyphenyl)sulfonyl]-3-(2-methoxy-phenyl)-2-oxo-2,3-dihydro-1H-indol-3-yl]-4-hydroxy-N,N-dimethyl-2-pyrrolidine carboxamide (SSR149415) using human embryonic kidney 293 cells stably expressing the three cloned mouse vasopressin receptors (V1a, V1b, and V2). A radioligand binding study showed that SR49059 and OPC-21268 potently inhibited [3H]AVP binding to the cloned mouse V1a receptor, with Ki values of 27 and 510 nM, respectively, whereas SSR149415 potently inhibited [3H]AVP binding to the cloned mouse V1b receptor with a Ki value of 110 nM. The inhibitory effects of vasopressin antagonists on AVP-induced insulin release correlate well with the rank order of potency to inhibit [3H]AVP binding to the V1b receptor; pancreatic islet cells were significantly inhibited by SSR149415 but not by SR49059 or OPC-21268. Furthermore, the AVP effect on insulin release was entirely lost in mice lacking the V1b receptor but was preserved in mice lacking the V1a receptor. Our study, which combined pharmacological and knockout approaches, clearly demonstrates that vasopressin-stimulated insulin release from islet cells is mediated via V1b receptors.