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From the Research Center, Maisonneuve-Rosemont Hospital, Department of Medicine, University of Montréal, Québec, Canada.
Correspondence to János G. Filep, MD, Research Center, Maisonneuve-Rosemont Hospital, Department of Medicine, University of Montréal, 5415 boulevard de l'Assomption, Montréal, Québec, Canada H1T 2M4.
Abstract To assess the role of nitric oxide (NO) produced by the constitutive (cNOS) and inducible NO synthase (iNOS) in the regulation of vascular functions, we compared the effects of aminoguanidine, a relatively selective inhibitor of iNOS, and NG-nitro-L-arginine methyl ester (L-NAME), a nonselective NOS inhibitor on blood pressure, plasma volume, and albumin escape during the early and delayed phases of endotoxin shock in conscious, chronically catheterized rats. Red blood cell volume and plasma volume were determined by using chromium-51tagged erythrocytes and iodine-125labeled albumin, respectively. Injection of lipopolysaccharide (LPS) 10 mg/kg IV resulted in a fall in blood pressure, hemoconcentration, and increased total-body albumin escape, which is reflected by a 25% reduction in plasma volume. When LPS was injected into animals pretreated with L-NAME (7.4 µmol/kg IV 15 minutes before LPS), losses in plasma volume and albumin escape were significantly greater than in rats that received LPS alone, despite that L-NAME attenuated the hypotensive action of LPS. Aminoguanidine pretreatment (162 µmol/kg) had no effect on the early responses to LPS, whereas it was as potent as L-NAME in reversing hypotension when injected 70 minutes after LPS. Aminoguanidine treatment also prevented further losses in plasma volume and markedly attenuated total-body and organ albumin escape rates elicited by LPS. L-NAME produced only a slight attenuation of LPS-induced losses in plasma volume and albumin escape in most organs studied, whereas it potentiated albumin extravasation in the lung. These results demonstrate that inhibition of cNOS potentiates, whereas inhibition of iNOS markedly attenuates, losses in plasma volume and albumin escape elicited by LPS, and suggest that selective inhibitors of iNOS may be more effective than nonselective inhibitors of all forms of NOS in the therapy of septic shock.
Key Words: aminoguanidine NG-nitro-L-arginine methyl ester vascular permeability septic shock nitric oxide
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