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Nitric oxide generation by renal proximal tubules: role of nitric oxide in the cytotoxicity of lipid A

LA Traylor, JW Proksch, VC Beanum and PR Mayeux

Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, USA.

Lipid A, the biologically active component of lipopolysaccharide, stimulated nitric oxide (NO) production by isolated rat proximal tubules (as measured by NO2- release) in a time-dependent manner. At a concentration of 50 micrograms/ml, lipid A stimulated NO2- generation and guanosine 3',5'-cyclic phosphate (cGMP) production within 5 min. Both of these effects were blocked by NG-methyl-L-arginine (L-NMMA), an inhibitor of NO synthase or by 8-(N,N'-diethylamino)-octyl-3,4,5- trimethoxybenzoate (TMB-8), an inhibitor of intracellular Ca++ release. Because an increase in NO production may be cytotoxic, we examined the cytotoxic potential of lipid A. At 90 min, lipid A (50 micrograms/ml) produced significant lactate dehydrogenase release (42 +/- 5%) compared to control (25 +/- 5%; P < .05). Both L-NMMA (1 mM) and TMB-8 (100 microM) completely protected against lipid A-induced cytotoxicity. TMB- 8 but not L-NMMA inhibited the rise intracellular Ca++ concentration ([Ca++]i) in isolated proximal tubules elicited by lipid A. L-NMMA but not TMB-8 inhibited proximal tubule soluble NO synthase activity. Thus, in the proximal tubule, lipid A stimulates a rise in [Ca++]i that in turn activates constitutive NO synthase. Furthermore, these events lead ultimately to NO-dependent cytotoxicity. Therefore, these findings suggest the potential for lipopolysaccharide to have a direct impact on proximal tubule physiology and renal function in vivo and support the potential therapeutic benefits of NO synthase inhibitors in the treatment of endotoxemia.

Volume 279, Issue 1, pp. 91-96, 10/01/1996
Copyright © 1996 by American Society for Pharmacology and Experimental Therapeutics




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Copyright © 1996 by the American Society for Pharmacology and Experimental Therapeutics.