The effects of nitric oxide inhibition on regional hemodynamics during hyperdynamic endotoxemia

NADPH phagocyte oxidase knockout mice control Trypanosoma cruzi proliferation, but develop circulatory collapse and succumb to infection

(•)NO is considered to be a key macrophage-derived cytotoxic effector during Trypanosoma cruzi infection. On the other hand, the microbicidal properties of reactive oxygen species (ROS) are well recognized, but little importance has been attributed to them during in vivo infection with T. cruzi. In order to investigate the role of ROS in T. cruzi infection, mice deficient in NADPH phagocyte oxidase (gp91(phox) (-/-) or phox KO) were infected with Y strain of T. cruzi and the course of infection was followed. phox KO mice had similar parasitemia, similar tissue parasitism and similar levels of IFN-γ and TNF in serum and spleen cell culture supernatants, when compared to wild-type controls. However, all phox KO mice succumbed to infection between day 15 and 21 after inoculation with the parasite, while 60% of wild-type mice were alive 50 days after infection. Further investigation demonstrated increased serum levels of nitrite and nitrate (NOx) at day 15 of infection in phox KO animals, associated with a drop in blood pressure. Treatment with a NOS2 inhibitor corrected the blood pressure, implicating NOS2 in this phenomenon. We postulate that superoxide reacts with (•)NO in vivo, preventing blood pressure drops in wild type mice. Hence, whilst superoxide from phagocytes did not play a critical role in parasite control in the phox KO animals, its production would have an important protective effect against blood pressure decline during infection with T. cruzi.

DTPA Fe(III) decreases cytokines and hypotension but worsens survival with Escherichia coli sepsis in rats

OBJECTIVE

Nonselective inhibition of nitric oxide (NO) with NO synthase antagonists decreases hypotension but worsens outcome clinically. We investigated whether iron (III) complex of diethylenetriaminepentaacetic acid [DTPA Fe(III)], a scavenger of NO as well as other oxidant mediators, has similar divergent effects in E. coli challenged rats.

METHODS

Animals with venous and arterial catheters and challenged with intrabronchial or intravenous E. coli were randomized to treatment with DTPA Fe(III) in doses from 3 to 800 mg/kg or placebo. Mean blood pressure (MBP) was measured in all animals and plasma NO, cytokines, and blood and lung leukocyte and bacteria counts in animals administered intrabronchial E. coli and DTPA Fe(III) 50 mg/kg or placebo. Animals received antibiotics and were observed 168 h.

RESULTS

Independent of drug regimen or infection site, compared to placebo, DTPA Fe(III) increased MBP although this was greater with high vs. lower doses. Despite increased MBP, DTPA Fe(III) worsened the hazards ratio of survival . At 6 and 24 h DTPA Fe(III) decreased NO but not significantly and decreased four cytokines (tumor necrosis factor-alpha, interleukins 1 and 10, and macrophage inflammatory protein 3alpha) and lung lavage neutrophils. From 6 to 24 h DTPA Fe(III) increased blood bacteria.

CONCLUSIONS

DTPA Fe(III) while increasing blood pressure has the potential to worsen outcome in sepsis. Further preclinical testing is required before this agent is applied clinically.

Renal Vascular Resistance in Sepsis

AIMS

To assess changes in renal vascular resistance (RVR) in human and experimental sepsis and to identify determinants of RVR.

METHODS

We performed a systematic interrogation of two electronic reference libraries using specific search terms. Subjects were animals and patients involved in experimental and human studies of sepsis and septic acute renal failure, in which the RVR was assessed. We obtained all human and experimental articles reporting RVR during sepsis. We assessed the role of various factors that might influence the RVR during sepsis using statistical methods.

RESULTS

We found no human studies, in which the renal blood flow (and, therefore, the RVR) was measured with suitably accurate direct methods. Of the 137 animal studies identified, 52 reported a decreased RVR, 16 studies reported no change in RVR, and 69 studies reported an increased RVR. Consciousness of animals, duration of measurement, method of induction of sepsis, and fluid administration had no effect on the RVR. On the other hand, on univariate analysis, size of the animals (p < 0.001), technique of measurement (p = 0.017), recovery after surgery (p = 0.004), and cardiac output (p < 0.001) influenced the RVR. Multivariate analysis, however, showed that only cardiac output (p = 0.028) and size of the animals (p = 0.031) remained independent determinants of the RVR.

CONCLUSIONS

Changes in RVR during sepsis in humans are unknown. In experimental sepsis, several factors not directly related to sepsis per se appear to influence the RVR. A high cardiac output and the use of large animals predict a decreased RVR, while a decreased cardiac output and the use of small animals predict an increased RVR.

Nitric oxide is not a mediator of inflammation-induced resistance to atracurium

Resistance to atracurium as a result of increased drug binding to alpha1-acid glycoprotein is associated with increased inducible nitric oxide synthase activity and increased nitric oxide levels in plasma. We investigated if the inhibition of inducible nitric oxide synthase and suppression of nitric oxide can reverse the resistance to atracurium. As a model of alpha1-acid glycoprotein and nitric oxide increase, 84 male Sprague-Dawley rats received an IV injection of either 60 mg/kg Corynebacterium parvum (CP) or saline (control). The 2 groups (CP/Control) were further divided into subgroups, receiving the selective inducible nitric oxide synthase inhibitor, N-Iminolysine, via drinking water at different concentrations. On day 4 post-CP injection, the pharmacodynamics of atracurium were determined. Plasma concentrations of nitric oxide, atracurium, and alpha1-acid glycoprotein were measured and acetylcholine receptor numbers were quantified. In the CP groups, N-Iminolysine suppressed nitric oxide levels in a dose-dependent manner. Resistance to atracurium persisted. alpha1-acid glycoprotein serum levels remained increased in all CP groups with no differences in acetylcholine receptor expression. Our results suggest that the mechanism leading to increased expression of alpha1-acid glycoprotein and consecutive increased protein binding of atracurium is not mediated by inducible nitric oxide synthase induction and nitric oxide expression.

Comparative analysis of the neuronal activation and cardiovascular effects of nitroglycerin, sodium nitroprusside and l-arginine

In this study, we compare the biological effects, Fos expression and cardiovascular responses induced in the rat, of different nitric oxide modulators (nitroglycerin, sodium nitroprusside and L-arginine). Nitroglycerin and sodium nitroprusside induced a similar pattern of neuronal activation in several areas, which include the paraventricular and supraoptic nuclei of the hypothalamus, central nucleus of the amygdala, parabrachial nucleus, locus coeruleus, ventrolateral medulla and nucleus tractus solitarius. However, only nitroglycerin activated the periaqueductal grey and nucleus trigeminalis caudalis. L-arginine-induced neuronal activation was restricted to the paraventricular and supraoptic nuclei of the hypothalamus. As regards cardiovascular effect, both nitroglycerin and sodium nitroprusside induced moderate hypotension (nitroglycerin: -23.3%, sodium nitroprusside: -24.3%) that lasted 40 min in the case of sodium nitroprusside and 80 min in the case of nitroglycerin. L-arginine did not significantly influence blood pressure. These data suggest that nitroglycerin, sodium nitroprusside and L-arginine are associated with different biological effects on both the central nervous system and the cardiovascular system. Of the NO-related drugs tested in this study, only nitroglycerin confirmed its ability to activate brainstem areas implicated in nociception.

Renal blood flow in sepsis

Introduction

To assess changes in renal blood flow (RBF) in human and experimental sepsis, and to identify determinants of RBF.

Method

Using specific search terms we systematically interrogated two electronic reference libraries to identify experimental and human studies of sepsis and septic acute renal failure in which RBF was measured. In the retrieved studies, we assessed the influence of various factors on RBF during sepsis using statistical methods.

Results

We found no human studies in which RBF was measured with suitably accurate direct methods. Where it was measured in humans with sepsis, however, RBF was increased compared with normal. Of the 159 animal studies identified, 99 reported decreased RBF and 60 reported unchanged or increased RBF. The size of animal, technique of measurement, duration of measurement, method of induction of sepsis, and fluid administration had no effect on RBF. In contrast, on univariate analysis, state of consciousness of animals (P = 0.005), recovery after surgery (P < 0.001), haemodynamic pattern (hypodynamic or hyperdynamic state; P < 0.001) and cardiac output (P < 0.001) influenced RBF. However, multivariate analysis showed that only cardiac output remained an independent determinant of RBF (P < 0.001).

Conclusion

The impact of sepsis on RBF in humans is unknown. In experimental sepsis, RBF was reported to be decreased in two-thirds of studies (62 %) and unchanged or increased in one-third (38%). On univariate analysis, several factors not directly related to sepsis appear to influence RBF. However, multivariate analysis suggests that cardiac output has a dominant effect on RBF during sepsis, such that, in the presence of a decreased cardiac output, RBF is typically decreased, whereas in the presence of a preserved or increased cardiac output RBF is typically maintained or increased.

Effects of an aqueous extract of cocoa on nitric oxide production of macrophages activated by lipopolysaccharide and interferon-gamma

OBJECTIVE

Macrophages are the primary targets of bacterial lipopolysaccharide (LPS). The effects of cocoa extract on production of nitric oxide (NO) by murine J774.1 macrophages activated by LPS and interferon-gamma (IFN-gamma) were examined.

METHODS

Cocoa was suspended in heated water and centrifuged, and the supernatant was then filtered. Nitrite was measured as a quantitative indicator of NO by spectrophotometry. LPS (1.0 mg/mL) and IFN-gamma (100 U/mL) were added to cultured macrophages with 0.05% cocoa extract, 0.25% cocoa extract, or pure water. NO synthesis by macrophages was significantly inhibited by cocoa extract (P < 0.01).

RESULTS

The inhibitory effect increased with concentration of the extract (P < 0.01). IFN-gamma (100 U/mL) and, later, LPS (100 microgram/mL) were added, together with 2.0% cocoa or pure water, to cultured macrophages. An inhibitory effect on NO production was observed on addition of only IFN-gamma, but more significant effects were obtained with addition of LPS (P < 0.01) and addition of both was most effective (P < 0.01).

CONCLUSIONS

These data suggested that cocoa extract contains a suppressor of NO production in murine macrophages activated by LPS and IFN-gamma. This effect does not appear to be caused merely by neutralization of LPS.

L-arginine supplementation in hyperdynamic endotoxemic pigs: effect on nitric oxide synthesis by the different organs

OBJECTIVES

Under septic conditions, the protective role of nitric oxide in the organs may become compromised at a time of increased demand as a result of decreased availability of L-arginine. It remains unknown whether supplementation with L-arginine, as a substrate, can modulate organ nitric oxide production.

DESIGN

Controlled study with laboratory animals.

SETTING

University research laboratory.

SUBJECTS

Female crossbred pigs.

INTERVENTION

Pigs were challenged with Escherichia coli endotoxin (intravenously) and received intravenous fluid resuscitation for 24 hrs to reproduce a model of long-lasting hyperdynamic endotoxemia. Pigs were infused with either L-arginine or L-alanine intravenously during endotoxin and via the intragastric route after cessation of endotoxin infusion. The effects of L-arginine supplementation on nitric oxide synthesis and the relationships with arginine metabolism were determined with a stable isotope infusion protocol. Also, organ nitrite plus nitrate fluxes were measured. Implantation of multiple catheters enabled in vivo measurements across the hindquarter muscle, the portal-drained viscera, the liver, and the kidneys.

MEASUREMENTS AND RESULTS

The isotope conversion method showed that L-arginine intervention significantly increased nitric oxide production by the portal-drained viscera, liver, and kidneys, resulting in elevated whole-body nitric oxide synthesis under endotoxemic and postendotoxemic conditions. Organ nitrite plus nitrate fluxes only tended to increase because of high variance among data.

CONCLUSIONS

In this endotoxemia model, supplemental use of L-arginine favored nitric oxide synthesis in various organs.

Combined prostaglandin and nitric oxide inhibition produces anatomic remodeling and closure of the ductus arteriosus in the premature newborn baboon

After birth, the full-term ductus arteriosus actively constricts and undergoes extensive histologic changes that prevent subsequent reopening. These changes are thought to occur only if a region of intense hypoxia develops within the ductus wall after the initial active constriction. In preterm infants, indomethacin-induced constriction of the ductus is often transient and is followed by reopening. Prostaglandins and nitric oxide both play a role in inhibiting ductus closure in vitro. We hypothesized that combined inhibition of both prostaglandin and nitric oxide production (with indomethacin and N-nitro-L-arginine (L-NA), respectively) may be required to produce the degree of functional closure that is needed to cause intense hypoxia. We used preterm (0.67 gestation) newborn baboons that were mechanically ventilated for 6 d: 6 received indomethacin alone, 7 received indomethacin plus L-NA, and 16 received no treatment (control). Just before necropsy, only 25% of control ductus and 33% of indomethacin-treated ductus were closed on Doppler examination; in contrast, 100% of the indomethacin-plus-L-NA-treated ductus were closed. Control and indomethacin-treated baboons developed negligible-to-mild ductus hypoxia (EF5 technique). Similarly, there was minimal evidence of ductus remodeling. In contrast, indomethacin-plus-L-NA-treated baboons developed intense hypoxia in regions where the ductus was most constricted. The hypoxic muscle strongly expressed vascular endothelial growth factor, and proliferating luminal endothelial cells filled and occluded the lumen. In addition, cells in the most hypoxic regions were undergoing DNA fragmentation. In conclusion, preterm newborns are capable of remodeling their ductus, just like the full-term newborn, if they can reduce their luminal blood flow to a point that produces intense ductus wall hypoxia. Combined prostaglandin and nitric oxide inhibition may be necessary to produce permanent closure of the ductus and prevent reopening in preterm infants.

Is nitric oxide overproduction the target of choice for the management of septic shock?

Sepsis is a heterogeneous class of syndromes caused by a systemic inflammatory response to infection. Septic shock, a severe form of sepsis, is associated with the development of progressive damage in multiple organs, and is a leading cause of patient mortality in intensive care units. Despite important advances in understanding its pathophysiology, therapy remains largely symptomatic and supportive. A decade ago, the overproduction of nitric oxide (NO) had been discovered as a potentially important event in this condition. As a result, great hopes arose that the pharmacological inhibition of NO synthesis could be developed into an efficient, mechanism-based therapeutic approach. Since then, an extraordinary effort by the scientific community has brought a deeper insight regarding the feasibility of this goal. Here we present in summary form the present state of knowledge of the biological chemistry and physiology of NO. We then proceed to a systematic review of experimental and clinical data, indicating an up-regulation of NO production in septic shock; information on the role of NO in septic shock, as provided by experiments in transgenic mice that lack the ability to up-regulate NO production; effects of pharmacological inhibitors of NO production in various experimental models of septic shock; and relevant clinical experience. The accrued evidence suggests that the contribution of NO to the pathophysiology of septic shock is highly heterogeneous and, therefore, difficult to target therapeutically without appropriate monitoring tools, which do not exist at present.

Nitric oxide inhalation and nitric oxide synthase inhibitor supplement for endotoxin-induced hypotension

BACKGROUND

This study was performed to determine whether a combined therapy of nitric oxide (NO) inhalation and nitric oxide synthase (NOS) inhibitor is effective in experimental animals with endotoxin-induced refractive hypotension accompanied by pulmonary hypertension.

METHODS

Escherichia coli lipopolysaccharide (1 mg/kg) was administered to 10 newborn piglets to induce endotoxemia. The experiment then began 60 min later, when the systemic arterial pressure dropped. The inhalation of 20 p.p.m. NO at 60 and 120 min of endotoxemia created a control group. Another group was also administered N w-nitro-L-arginine (L-NNA; 5 mg) after the first NO inhalation at 60 min of endotoxemia (the L-NNA group). Pulmonary arterial pressure, systemic arterial pressure and cardiac output were measured and compared among the groups.

RESULTS

Three of the 5 piglets in the control group died of hypotensive shock, while in the L-NNA group the systemic arterial pressure recovered to pre-endotoxin administration levels. The L-NNA group produced a further increase in pulmonary arterial pressure against which NO inhalation was effective.

CONCLUSION

Nitric oxide inhalation alone carries a potential risk of further lowering systemic arterial pressure in a piglet with hypotension induced by endotoxin, whereas the combined therapy resulted in the recovery of the blood pressure to pre-endotoxin levels. The combined therapy was simultaneously effective against pulmonary hypertension.

Peroxynitrite attenuates hepatic ischemia-reperfusion injury

In the present study, we examined the effects of peroxynitrite on reperfusion injury using a rat model of hepatic ischemia-reperfusion (HI/R). The left and median lobes of the liver were subjected to 30 min of ischemia, followed by 4 h of reperfusion. Groups A and B rats were sham-operated controls that received vehicle or peroxynitrite; groups C and D rats were subjected to HI/R and received peroxynitrite or vehicle, respectively. A dose of 2 micromol/kg body wt of peroxynitrite, diluted in saline (pH 9.0, 4 degrees C), was administered as a bolus through a portal vein catheter at 0, 60, and 120 min after reperfusion. Results showed that superoxide generation in the ischemic lobes of the liver and plasma alanine aminotransferase (ALT) activity of group C were decreased by 43% and 45%, respectively, compared with group D. Leukocyte accumulations in the ischemic lobes of liver and circulating leukocytes were decreased by 40% and 27%, respectively, in group C vs. D. The ratios of mRNA of P-selectin and intercellular adhesion molecule-1 (ICAM-1) to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA extracted from the ischemic lobes of the liver of group C were decreased compared with group D. There were no differences between the groups A and B in terms of plasma ALT activity, circulating leukocytes, superoxide generation, and leukocyte infiltration in the ischemic lobes of the liver. Moreover, hemodynamic parameters (i.e., mean arterial blood pressure, cardiac index, stroke index, and systemic vascular resistance) were not significantly different among groups B, C, and D. These results suggest that administration of peroxynitrite via the portal vein only has a local effect. Exogenous peroxynitrite at physiological concentrations attenuates leukocyte-endothelial interaction and reduces leukocyte infiltration. The mechanism of the reduction of leukocyte infiltration into ischemic lobes of the liver appears because of decreased expression of mRNA of P-selectin and ICAM-1. The net effect of administration of peroxynitrite may be to reduce adhesion molecule-mediated, leukocyte-dependent reperfusion injury.

Nitric oxide synthase inhibition increases venular leukocyte rolling and adhesion in septic rats

OBJECTIVE

Excess production of nitric oxide (NO) has been implicated in hypotension and blood flow abnormalities in sepsis, but NO is also an important inhibitor of leukocyte rolling and adhesion. Leukocyte adhesion is increased in sepsis despite elevated NO production. We hypothesized that inhibition of NO synthase (NOS) could increase leukocyte adhesion in sepsis.

DESIGN

Prospective animal study.

SETTING

Experimental animal laboratory.

SUBJECTS

Twenty-five male rats, anesthetized with ketamine and acepromazine.

INTERVENTIONS

Topical superfusion of the nonselective NOS inhibitor N(G)-monomethyl-L-arginine (NMA) on skeletal muscle postcapillary venules.

MEASUREMENTS AND MAIN RESULTS

Rats made septic by cecal ligation and puncture were compared with controls that underwent sham ligation. Leukocyte rolling and adhesion were measured in cremasteric postcapillary venules of septic and control rats using in vivo videomicroscopy. The effects of NOS inhibition on leukocyte rolling and adhesion were also measured. After a stable baseline was reached, 1 microM of the nonselective NOS inhibitor NMA was suffused topically followed by physiologic buffer. The effects of L-arginine on leukocyte rolling and adhesion were also measured, both before and after suffusion of NMA. Leukocyte rolling and adhesion was increased in septic rats as compared with controls (control 5.5+/-0.9 rolling cells/min, 1.0+/-0.3 adherent cells/min; septic 13.7+/-2.0 rolling cells/min, 3.1+/-0.6 adherent cells/min; p < .001), and NOS inhibition further increased leukocyte rolling and adhesion in both septic and control rats (control 14.0+/-1.7 rolling cells/min, 2.8+/-0.5 adherent cells/min; septic 25+/-2.1 rolling cells/min, 5.4+/-0.5 adherent cells/min; both p < .001 vs. baseline). Prior suffusion of excess L-arginine prevented the increase in leukocyte adhesion with NMA in septic rats (2.6+/-0.4 adherent cells/min vs. 3.0+/-0.6 adherent cells/min; n = 3; p > .05). When administered after NMA, excess L-arginine partially reversed leukocyte adhesion in septic rats (5.4+/-0.7 adherent cells/min, with NMA vs. 4.3+/-0.7 adherent cells/min, after L-arginine; n = 5; p < .05). Venular shear did not differ between septic and control rats (600+/-109 (sec(-1)) vs. 620+/-37 (sec(-1)); p > .05).

CONCLUSIONS

Although NOS inhibition may ameliorate hypotension in sepsis, such therapy may be deleterious by increasing leukocyte adhesion.

Cardiac contractility is not depressed in early canine endotoxic shock

We investigated effects of acute endotoxemia (Escherichia coli endotoxin, 1 mg/kg, intravenously) on left ventricular (LV) function in the first 4 h after induction of endotoxic shock in anesthetized canine preparations (n = 7 each, endotoxin and control groups). LV pressure and conductance (volume) catheters were used to construct pressure-volume loops. Transient inferior vena cava occlusion was used to rapidly and reversibly alter LV end-diastolic volume. LV contractility was assessed from the slope of the LV end-systolic pressure-volume relationship (Ees) and from preload-recruitable stroke work (PRSW), and from their change (DeltaEes and DeltaPRSW, respectively, measured at 2 and 4 h only), in response to a dobutamine infusion (5 microg/kg/min). Diastolic function and arterial tone were assessed as the maximal negative change in filling pressure versus time (max -dP/dt), filling rate, and arterial elastance (Ea), respectively. Ees, PRSW, Ea, diastolic function, and hemodynamics were measured hourly. Endotoxemia induced an immediate hypotensive, hyperdynamic, tachycardic state with progressive lactic acidosis. By 2.5 h after endotoxin infusion, heart rate returned to preendotoxin and control levels, but the other changes remained. However, no change occurred in LV Ees, DeltaEes, PRSW, DeltaPRSW, diastolic function, or Ea during the 4-h measurement interval. The cardiovascular collapse seen during the first 4 h of endotoxemia is therefore not due even partly to alterations in LV contractility.

Norepinephrine and nomega-monomethyl-L-arginine in porcine septic shock: effects on hepatic O2 exchange and energy balance

We compared the effects of norepinephrine (NOR; n = 11) and the nonselective nitric oxide synthase inhibitor Nomega-monomethyl-L-arginine (L-NMMA; n = 11) on hepatic blood flow (Q liv), O2 exchange, and energy metabolism over 24 h of hyperdynamic, normotensive porcine endotoxic shock. Endotoxin (ETX; n = 8) caused a continuous fall in mean arterial pressure (MAP) despite a sustained 50% increase in cardiac output (Q) achieved by adequate fluid resuscitation. NOR maintained MAP at preshock levels owing to a further rise in Q, while the comparable hemodynamic stabilization during L-NMMA infusion resulted from systemic vasoconstriction, increasing the systemic vascular resistance (SVR) about 30% from shock level after 6 h of treatment concomitant with a reduction in Q to preshock values. Whereas NOR also increased Q liv and, hence, hepatic O2 delivery (hDO2), but did not affect hepatic O2 uptake (hVO2), L-NMMA influenced neither Q liv nor hDO2 and hVO2. Mean capillary hemoglobin O2 saturation (HbScO2) on the liver surface as well as HbScO2 frequency distributions, which mirror microcirculatory O2 availability, remained unchanged as well. Neither treatment influenced the ETX-induced derangements of cellular energy metabolism reflected by the progressive decrease in hepatic lactate uptake rate and increased hepatic venous lactate/pyruvate ratios. ETX nearly doubled the endogenous glucose production (EGP) rate, which was further increased with NOR, whereas L-NMMA nearly restored EGP to preshock levels. Nevertheless, despite the different mechanisms in maintaining blood pressure neither treatment influenced ETX-induced liver dysfunction.

NO modulates P-selectin and ICAM-1 mRNA expression and hemodynamic alterations in hepatic I/R

The anti-inflammatory role of nitric oxide (NO) was studied in a model of hepatic ischemia-reperfusion (I/R) in rats. Male Fischer rats were subjected to 30 min of no-flow ischemia of the left and median lobes of the liver, and animals were examined for a 4-h period of reperfusion. The animals were divided into the following groups: control-vehicle; I/R-vehicle; I/R-Nomega-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg iv, 10 min before reperfusion); sham control-L-NAME, and I/R-S-nitroso-N-acetyl-penicillamine (SNAP, 25 micromol/kg iv, 10 min before reperfusion, followed by 20 micromol. kg-1. h-1 in 1.0 ml saline infused for 4 h). Results showed that mean arterial blood pressure was significantly increased in the sham control-L-NAME or I/R-L-NAME groups compared with either the I/R-vehicle or I/R-SNAP groups. However, cardiac index (CI) and stroke volume index (SVI) were markedly decreased, and systemic vascular resistance index (SVRI) was dramatically increased. Interestingly, the CI and SVI in rats treated with SNAP were markedly improved over that of the I/R group. Plasma nitrate and nitrite levels were significantly decreased in the I/R-L-NAME group; however, superoxide generation in the ischemic lobes and plasma alanine aminotransferase activity were higher compared with I/R-SNAP rats. The L-NAME-induced enhancement of hepatic injury in rats with I/R may be due in part to neutrophil infiltration, which was significantly increased compared with animals subjected to I/R or I/R-SNAP. The mechanism of L-NAME-enhanced neutrophil infiltration may be due to the fact that the ratios of P-selectin and intercellular adhesion molecule 1 (ICAM-1) mRNA to glyceraldehyde-3-phosphate dehydrogenase mRNA extracted from the ischemic lobes of I/R-L-NAME rats were significantly increased when compared with the I/R-SNAP group. These results suggest that 1) endogenous NO reduces the SVRI and permits an increased CI and SVI; 2) exogenous NO further improves CI and SVI; and 3) endogenous, but not exogenous, NO decreases P-selectin and ICAM-1 mRNA expression, thereby reducing polymorphonuclear neutrophil-dependent reperfusion tissue injury.

Inhaled nitric oxide prevents left ventricular impairment during endotoxemia

We evaluated the effect of long-term inhalation of nitric oxide (NO) on cardiac contractility after endotoxemia by using the end-systolic elastance of the left ventricle (LV) as a load-independent contractility index. Chronic instrumentation in 12 pigs included implantation of two pairs of endocardial dimension transducers to measure LV volume and a micromanometer to measure LV pressure. One week later, the animals were divided into a control group (n = 6) or a NO group (n = 6). All animals received intravenous Escherichia coli endotoxin (10 micrograms. kg-1. h-1) and equivalent lactated Ringer solution. NO inhalation (20 parts/million) was begun 30 min after the initiation of endotoxemia and was continued for 24 h. In both groups, tachycardia, pulmonary hypertension, and systemic hyperdynamic changes were noted. The end-systolic elastance in the control group was significantly decreased beyond 7 h. NO inhalation maintained the end-systolic elastance at baseline levels and prevented its impairment. These findings indicate that NO exerts a protective effect on LV contractility in this model of endotoxemia.

Intrarenal haemodynamics and renal dysfunction in endotoxaemia: effects of nitric oxide synthase inhibition

1. This study investigated the effects of low dose endotoxin (lipopolysaccharide, LPS) on (i) systemic haemodynamics, (ii) renal blood flow (RBF), (iii) renal cortical and medullary perfusion and (iv) renal function in the anaesthetized rat. We have also investigated the effects of nitric oxide (NO) synthase (NOS) inhibition with NG-methyl-L-arginine (L-NMMA) on the alterations in systemic and renal haemodynamics and renal function caused by endotoxin. 2. Infusion of low dose LPS (1 mg kg-1 over 30 min, n = 6) caused a late fall in mean arterial blood pressure (MAP, at 5 and 6 h after LPS), but did not cause an early (at 1-4 h after LPS) hypotension. The pressor effect of noradrenaline (NA, 1 microgram kg-1, i.v.) was significantly reduced at 1 to 6 h after LPS (vascular hyporeactivity). Infusion of L-NMMA (50 micrograms kg-1 min-1 commencing 60 min before LPS and continued throughout the experiment, n = 7) abolished the delayed hypotension and significantly attenuated the vascular hyporeactivity to NA (at 2-6 h). 3. Infusion of LPS (1 mg kg-1 over 30 min, n = 6) caused a rapid (within 2 h) decline in renal function (measured by inulin clearance) in the absence of a significant fall in MAP or renal blood flow (RBF). L-NMMA (n = 7) attenuated the impairment in renal function caused by LPS so that the inulin clearance in LPS-rats treated with L-NMMA was significantly greater than in LPS-rats treated with vehicle (control) at 3-6 h after infusion of LPS. 4. Endotoxaemia also caused a significant reduction in renal cortical, but not medullary perfusion (measured as Laser Doppler flux). Infusion of L-NMMA caused a significant further fall in cortical perfusion and a significant fall in medullary perfusion in the absence of changes in RBF. 5. Infusion of LPS resulted in a progressive increase in the plasma levels of nitrite/nitrate (an indicator of the formation of NO), so that the plasma concentration of nitrite/nitrate was significantly higher than baseline at 150 to 330 min after LPS. Infusion of L-NMMA attenuated the rise in the plasma concentration of nitrite/nitrate (at 270 and 330 min, P < 0.05) caused by LPS. 6. Thus, the renal dysfunction caused by injection of low dose of endotoxin in the rat occurs in the absence of significant falls in blood pressure or total renal blood flow. Inhibition of NOS activity with L-NMMA attenuates the renal dysfunction caused by endotoxin (without improving intrarenal haemodynamics), suggesting that an overproduction of NO may contribute to the development of renal injury and dysfunction by causing direct cytotoxic effects.

Nitric oxide and shock

Shock can be defined as the failure of the circulatory system to provide necessary cellular nutrients, including oxygen, and to remove metabolic wastes. Although it is now recognized that more than 100 different forms of shock exist, this recognition is more a reflection of the widespread use of the term to describe a variety of disease states. For the purpose of this monograph, we concentrate on various forms of cardiovascular shock, in particular, shock that may be linked to inappropriate vasodilation from overproduction of the endogenous vasodilator, nitric oxide. Some forms of shock have been extensively studied, and convincing evidence exists for the role of nitric oxide. Other disease states have been less well characterized in terms of their association with excess nitric oxide production. Available evidence of a role for nitric oxide is discussed in the hope of stimulating the interest of investigators to explore these areas more thoroughly.