Interleukin-1\g=b\-induced nitric oxide production from isolated rat islets is modulated by D-glucose and 3-isobutyl-1-methyl xanthine Henrik U Andersen, D\l=i'\dac Mauricio, Allan E Karlsen, Thomas Mandrup-Poulsen, Jens H Nielsen and J\l=o/\rn Nerup Steno Diabetes Center, and Hagedorn Research Institute , Gentofte, Denmark Andersen HU, Mauricio D, Karlsen AE, Mandrup-Poulsen T, Nielsen JH, Nerup J. Interleukin\x=req-\ nitric oxide production from isolated rat islets is modulated by d-glucose and 3-isobutyl-1-methyl xanthine. Eur J Endocrinol 1996:134:251-9. ISSN 0804-4643 Interleukin-1\g=b\ has been proposed to cause selective \g=b\-cell destruction via the induction of nitric oxide synthesis. The cytotoxic effect of interleukin-1\g=b\ is modulated by the concentration of d-glucose in the medium. The aim of this study was to investigate if d-glucose-mediated modulation of interleukin-1\g=b\ effects on insulin release from isolated rat islets was related to modulation of nitric oxide production. Further, we wished to investigate the effects of agents increasing the intracellular concentration of cAMP on interleukin-1\g=b\-induced nitrite production. We demonstrated that d-glucose potentiated interleukin-1\g=b\-induced nitrite production in rat islets without affecting the mRNA level of the inducible nitric oxide synthase. This effect was dissociated from interleukin-1\g=b\ action on insulin release, since a relative protection against interleukin-1\g=b\ effects on acute insulin release was found at high (28 mmol/l) concentrations of d-glucose, and blocking nitrite production by the L-arginine analog aminoguanidine, which selectively inhibits the cytokine-inducible nitric oxide synthase, did not result in protection against the inhibitory action of interleukin-1\g=b\ Neither l-glucose nor the secretagogues l-leucine, tolbutamide and \g=b\-isobutyl-1-methyl xanthine shared the potentiating effect of d-glucose, The phosphodiesterase inhibitor \g=b\-isobutyl-1-methyl xanthine reduced interleukin-1\g=b\-induced nitrite production at 3.3mmol/l d-glucose, an effect that could be reproduced by the cAMP analog dibutyryl cAMP. Addition of 3-isobutyl-1-methyl xanthine resulted in a threefold reduction in the mRNA level of interleukin-1\g=b\-induced inducible nitric oxide synthase. We conclude that interleukin-1\g=b\-induced islet nitric oxide synthesis is augmented by d-glucose but not by non-substrate secretagogues, and that secretagogues that elevate cAMP inhibit islet nitric oxide production. J\l=o/\rn Nerup, Steno Diabetes Center, Niels Steensens vej 2, DK-2820 Gentofte, Denmark The cytokine interleukin-1/? (IL-1/?) has been proposed as a pathogenetic factor in the initial events leading to insulin-dependent diabetes mellitus (1). Interleukin-1/? affects /?-cell function and morphology in rat islets in organ culture in a time- and dose-dependent manner, characterized by initial stimulation of insulin release followed by inhibition (i-3) with associated loss of islet DNA and selective /?-cell cytotoxicity (4, 5). The sensitivity to the deleterious effects if IL-1/? on islet integrity and insulin release is increased when the D-glucose concentration in the culture medium is raised from 3.3 to 11 mmol/1 (6). This has led to the hypothesis that the /?-cell is a "moving target" for IL-1/3 cytotoxicity, i.e. being more vulnerable when the functional activity is increased (7). The D-glucose-mediated potentiation of the inhibitory effect of IL-1/? on insulin release appears to be maximal between 11 and 20 mmol/1 of o-glucose, since the inhibitory effect was diminished when the d- glucose concentration was raised above 20 mmol/1 (5, 8, 9). These high concentrations of D-glucose have also been shown to protect /?-cells against the cytotoxic agents streptozotocin and alloxan (10). The free-radical nitric oxide (NO) has been implicated as a possible effector molecule in IL-l/?-mediated islet toxicity because IL-1/? induces islet NO production and because synthetic analogs of the substrate for NO, l- arginine, prevent IL-l/?-induced inhibition of insulin release (11). Nitric oxide is produced by the enzyme NO- synthase (NOS), of which three different types have been identified. Two constitutively expressed isoforms (cNOS) were originally cloned from endothelium and brain, and one inducible isoform (LNOS) was originally cloned from an activated macrophage cell line (12) and later also from IL-l/3-exposed rat islets (13). Beta cells have also been demonstrated to contain cNOS, presumed to mediate L-arginine-induced insulin release (14, 15). In endocrine islet cells, LNOS-mediated NO production appears to be specific to /3-cells because iNOS expression was induced by IL-1/? and IL·!/? + tumor necrosis factor alpha (TNF-a) or interferon gamma (IFN-7) in FACS-