Inhibition of nitric oxide generation: Normalization of in vitro insulin secretion in mice with multiple low-dose streptozotocin and in mice injected with mononuclear splenocytes from diabetic syngeneic donors

We studied the effect on in vitro glucose-induced insulin secretion of in vivo administration of l-NG-monomethyl-arginine (l-NMMA), a competitive inhibitor of nitric oxide (NO) synthase, to mice injected with multiple low-dose streptozotocin (mld-SZ). In addition, the effect of l-NMMA treatment on the capacity of mononuclear spleen cells (MS) from mld-SZ mice to transfer alterations in insulin secretion from normal syngeneic receptors was also investigated. We also studied the effect of in vivo treatment with l-NMMA on anti-β-cell cellular immune aggression (CIA) by coculturing MS from mld-SZ mice with rat dispersed islet cells. Our results show that mld-SZ mice treated with 0.25 mg l-NMMA/g body weight had normoglycemia, first- and second-phase glucose-stimulated insulin secretion similar to those obtained in nondiabetic mice—effects not observed with a lower dose of l-NMMA (0.17 mg/g body weight)—and a diminished anti-β-cell CIA. We also demonstrate that mice injected with MS from syngeneic donors treated with mld-SZ plus 0.25 mg l-NMMA/g had normal levels for first-phase glucose-stimulated insulin secretion and an absence of CIA. Taken together, these findings seem to indicate that prevention of in vivo NO production may block the onset of diabetes in mld-SZ mice, and that l-NMMA administration to diabetic donor mice prevents inhibition of first-phase insulin secretion and CIA in the transferred recipient mice. Although a nonimmunological mechanism or mechanisms of diabetes prevention by l-NMMA cannot be excluded, these results suggest that l-NMMA treatment could also be acting on T-cell-dependent immune reactions.