Increased Microvascular Reactivity and Improved Mortality in Septic Mice Lacking Inducible Nitric Oxide Synthase

Abstract

Abstract-Persistent vasodilation characteristic of septic shock may result from overproduction of nitric oxide and can lead to pressor-refractory hypotension and death. To evaluate the significance of cytokine-inducible nitric oxide synthase (iNOS) in the pathogenesis of sepsis, we used a clinically relevant mouse model of sepsis and compared mortality and microvascular reactivity in wild-type (WT) mice and transgenic mice deficient in iNOS. WT C57BL/6 and iNOS-deficient mice were made septic by cecal ligation and puncture. Treated mice were given fluids and antibiotics every 6 hours. Microvascular vasoconstriction in response to topical norepinephrine was measured in cremasteric arterioles (15 to 30 m) by videomicroscopy. Mortality at 48 hours was significantly lower in treated septic iNOS-deficient mice (45%) than in treated septic WT mice (76%), untreated septic iNOS-deficient mice (87%), or untreated WT mice (100%) (PϽ0.01). Norepinephrine-induced vasoconstriction was decreased in WT septic mice (EC 50 200Ϯ56 nmol/L) compared with WT and iNOS-deficient shams (16Ϯ4 and 13Ϯ6 nmol/L), and vasoconstriction was significantly improved in septic iNOS-deficient mice (35Ϯ13 nmol/L, PϽ0.01). Microvascular catecholamine responsiveness and survival were improved in iNOS-deficient mice in a clinically relevant model of sepsis, suggesting that iNOS plays an important, but not exclusive, role in refractory vasodilation in patients with septic shock. (Circ Res. 2000;86:774-779.)Key Words: sepsis Ⅲ vascular reactivity Ⅲ nitric oxide Ⅲ inducible nitric oxide synthase Ⅲ videomicroscopy T he characteristic hemodynamic abnormality in septic shock is persistent vasodilation with a normal or high cardiac output, which results in hypotension, hypoperfusion, and a high mortality. This vasodilation is often refractory to vasopressor therapy with catecholamines. Nitric oxide (NO), a potent endogenous vasodilator, has been implicated in vascular relaxation and hypotension in sepsis. 1 NO is synthesized from L-arginine by the enzyme NO synthase (NOS), which has constitutive and inducible isoforms encoded by distinct genes. 2 The inducible NOS isoform (iNOS) is present in macrophages, hepatocytes, and vascular smooth muscle cells; is regulated at the transcriptional level; and releases large amounts of NO in a sustained fashion after stimulation with mediators associated with sepsis, such as endotoxin, tumor necrosis factor, interleukin-1, interleukin-2, and interferon-␥. 2 Overproduction of NO by activation of iNOS has been well documented both in animal models of sepsis and in septic patients. [3][4][5][6] The vasodilatory effects of NO have been implicated in both the vascular relaxation associated with hypotension in sepsis 1,7 and in refractoriness to vasopressor catecholamines. 8,9 The major determinant of vascular resistance in the systemic circulation is the tone of resistance arterioles, as the principal pressure drop in the vascular tree occurs at the level of the microvasculature. 10 Previous studies in our laboratory have u...

Evidence for the Role of Reactive Nitrogen Species in Polymicrobial Sepsis-Induced Renal Peritubular Capillary Dysfunction and Tubular Injury

“…These studies are the first to examine the potential therapeutic benefits of pharmacologic inhibition of iNOS in CLP-induced AKI. In other models of CLP-induced sepsis, pharmacologic inhibition of iNOS prevents the fall in BP and other hemodynamic changes in the rat (36), and transgenic mice that are deficient in iNOS maintain arteriolar responsiveness to catecholamines and show improved survival (37). The appearance of nitrated proteins and oxidation products in the kidney during LPS-induced renal failure in rats and the ability of iNOS Figure 6 to determine capillary flow.…”

Activation of Acid Sphingomyelinase and Its Inhibition by the Nitric Oxide/Cyclic Guanosine 3′,5′-Monophosphate Pathway: Key Events in Escherichia coli-Elicited Apoptosis of Dendritic Cells

“…The survival to sepsis of iNOS Ϫ/Ϫ mice was found to be less than, more than, or equal to that of their w.t. counterparts depending on the model of endotoxemia, thus reflecting the complexity of the actions of NO described above (71)(72)(73)(74)(75). Despite this complexity, however, iNOSgenerated NO has been shown to contribute substantially to protection from apoptosis during sepsis in various organs, including liver, heart, kidney, and thymus (74, 76 -79).…”

Inhibition of Leukocyte Rolling by Nitric Oxide during Sepsis Leads to Reduced Migration of Active Microbicidal Neutrophils

“…Indeed, iNOS inhibitors prevent the decrease in systemic vascular resistance and unresponsiveness to catecholamines induced by experimental endotoxemia (29) and in patients with septic shock (42). Furthermore, iNOS-deficient (iNOS Ϫ/Ϫ ) mice subjected to cecal ligation and puncture (CLP) showed improved microvascular catecholamine responsiveness and survival compared with wild mice (28).…”