Imidazoline-induced amplification of glucose- and carbachol-stimulated insulin release includes a marked suppression of islet nitric oxide generation in the mouse S. Meidute-Abaraviciene, 1 H. Mosen, 1 I. Lundquist 2 and A. Salehi 1 1 Department of Clinical Science, Division of Endocrine Pharmacology, UMAS, Malmo ¨, Sweden 2 Department of Experimental Medical Science, University of Lund, Lund, Sweden Received 19 June 2008, revision requested 10 July 2008, revision received 14 August 2008, accepted 23 August 2008 Correspondence: S. Meidute- Abaraviciene, Department of Clinical Science, Division of Endocrine Pharmacology, University of Lund, CRC, S-205 02 Malmo ¨, Sweden. E-mail: sandra.meidute@med.lu.se Abstract Aim: The role of islet nitric oxide (NO) production in insulin-releasing mechanisms is unclear. We examined whether the beneficial effects of the imidazoline derivative RX 871024 (RX) on b-cell function might be related to perturbations of islet NO production. Methods: Experiments were performed with isolated islets or intact mice challenged with glucose or carbachol with or without RX treatment. Insulin was determined with radioimmunoassay, NO generation with high-perfor- mance liquid chromatography and expression of inducible NO synthase (iNOS) with confocal microscopy. Results: RX treatment, in doses lacking effects on basal insulin, greatly amplified insulin release stimulated by the NO-generating secretagogues glucose and carbachol both in vitro and in vivo. RX also improved the glucose tolerance curve. Islets incubated at high glucose levels (20 mmol L )1 ) displayed increased NO production derived from both neuronal constitutive NO synthase (ncNOS) and iNOS. RX abrogated this glucose-induced NO production concomitant with amplification of insulin release. Confocal microscopy revealed abundant iNOS expression in b cells after incubation of islets at high but not low glucose levels. This was abolished after RX treat- ment. Similarly, islets cultured for 24 h at high glucose levels showed intense iNOS expression in b cells. This was abrogated with RX and followed by an amplified glucose-induced insulin release. Conclusion: RX effectively counteracts the negative impact of b-cell NO generation on insulin release stimulated by glucose and carbachol suggesting imidazoline compounds by virtue of NOS inhibitory properties being of potential therapeutic value for treatment of b-cell dysfunction in hyper- glycaemia and type 2 diabetes. Keywords cholinergic stimulation, glucose stimulation, imidazoline RX 871024, insulin release, islet nitric oxide synthase isoenzymes. Over the last several years, a wide range of imidazoline compounds has been shown to have the capacity to amplify glucose-stimulated insulin release and thus being suggested as a new therapeutic approach to type 2 diabetes (reviewed by Morgan et al. 1999, Efendic et al. 2002). One of the most studied imidazoline derivatives is RX 871024 (hereafter called RX in the text) (Zaitsev et al. 1996, Mourtada et al. 1999, Efanov et al. 2001, 2002) which belongs to the so-called classical insulinotropic imidazolines possessing both the property to close the ATP-sensitive K + (K + ATP ) channel activity and having additional effects to directly Acta Physiol 2009, 195, 375–383 Ó 2008 The Authors Journal compilation Ó 2008 Scandinavian Physiological Society, doi: 10.1111/j.1748-1716.2008.01896.x 375