Involvement of Nitric Oxide in Nickel-Induced Hyperglycemia in Rats Sanjay Gupta, 1,2 Nihal Ahmad, 1 Mirza M. Husain, and Ramesh C. Srivastava Department of Chemical Toxicology, Division of Toxicokinetics, Industrial Toxicology Research Centre, P.O. Box 80, M. G. Marg, Lucknow 226 001, India Received August 11, 1999, and in revised form February 2, 2000 Nitric oxide is an important bioactive signaling molecule that mediates a variety of normal physio- logical functions which, if altered, could contribute to the genesis of many pathological conditions, in- cluding diabetes. In the present study we have shown the involvement of NO in nickel-induced hy- perglycemia in male albino rats. Administration of nickel chloride (25 to 100 mol/kg; ip) to overnight- fasted rats resulted in significant dose and time- dependent increase in plasma glucose, attaining maximum level at 1 h posttreatment and thereafter decreasing to normal levels by 4 h. The involvement of NO in nickel-induced hyperglycemia was evident by the observation that pretreatment of rats with NG-monomethyl-L-arginine (10 to 50 mol/kg; ip), an inhibitor of nitric oxide synthase (NOS), signifi- cantly attenuated the nickel-mediated increase in the plasma glucose levels in a dose-dependent fash- ion. The activity of Ca 2 -dependent NOS (constitu- tive form, c-NOS) was found to be significantly ele- vated in adrenals (5.5-fold) and brain (1.4-fold) at 1 and 2 h posttreatment, attaining normal levels by 4 h. In contrast, the activity of c-NOS in pancreas was significantly decreased (2.8-fold) with a con- comitant increase (11.6-fold) in inducible NOS (i- NOS) at the same time interval. As observed by im- munoblot analysis, a significant increase in i-NOS protein expression in the pancreas was observed at 1 and 2 h posttreatment. This was associated with a significant elevation in cGMP levels in adrenals, brain, and pancreas, possibly via the stimulation of cytosolic guanylate cyclase. This elevation in cGMP was abolished by low concentration of hemoglobin. These effects were associated with the accumula- tion of nickel in the target tissues. Taken together, our data suggest that nickel causes a significant increase in the levels of (i) cGMP and c-NOS in adrenals and brain and (ii) i-NOS in pancreas. These events may be responsible for modulating the release of insulin from pancreas finally leading to hyperglycemic condition in rats. © 2000 Academic Press Key Words: nitric oxide; nickel; hyperglycemia; NG-monomethyl-L-arginine; cyclic-GMP. A growing body of evidence suggests that nitric oxide, a free radical and a prominent vascular and neuronal messenger molecule responsible for endothelium-derived relaxing factor activity, may play a crucial role in the development and/or exac- erbation of various physiological and pathological processes (1, 2). NO is produced as a result of me- tabolism of L-arginine by nitric oxide synthase (NOS) 3 with NADPH and oxygen as cosubstrates in most of cell types (3, 4). Numerous mammalian cell 1 Present address: Department of Dermatology, Case Western Reserve University, 11100 Euclid Avenue, Cleveland, OH 44106. 2 To whom correspondence should be addressed. Fax: (216) 368-0212. E-mail: gxs44@po.cwru.edu. 3 Abbreviations used: NOS, nitric oxide synthase; cGMP, cyclic GMP; n-NOS, neuronal NOS; ec-NOS, endothelial cell constitu- tive NOS; i-NOS, inducible NOS; c-NOS, constitutive NOS; L-NMMA, NG-monomethyl-L-arginine; PMSF, phenylmethylsul- fonyl fluoride; STZ, streptozotocin. NITRIC OXIDE: Biology and Chemistry Vol. 4, No. 2, pp. 129 –138 (2000) doi:10.1006/niox.2000.0278, available online at http://www.idealibrary.com on 129 1089-8603/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved.