Selective inhibition of inducible nitric oxide synthase: effects on hemodynamics and regional blood flow in healthy and septic sheep

Multiple versus single injections of fluorescent microspheres for the determination of regional organ blood flow in septic sheep

Determination of regional blood flow by the injection of microspheres in sepsis models is crucial for the experimental evaluation of the influence of experimental treatment strategies on organ perfusion. However, multiple injections may critically increase the total quantity of microspheres, thereby restricting regional microcirculation and altering the results of blood flow measurements. This study was designed to compare the results of multiple versus single injections of microspheres in an established ovine sepsis model. Injury was induced by smoke inhalation and instillation of Pseudomonas aeruginosa into the lungs. Twenty sheep were studied for 4, 8, 12, 18, or 24 h, respectively. Microspheres were injected at the end of the study period and the animals were euthanized and organ tissues were harvested. Another four sheep were studied for 24 h and multiple microsphere injections were performed at the above indicated time points in the same animals. Tracheal blood flow significantly increased and blood flow to the pancreas and ileum significantly decreased versus baseline in both groups (P < 0.05 each). Blood flow to the ileum, renal cortex and skin did not significantly change versus baseline in both groups (P > 0.05). Blood flow was higher to the trachea in the multiple injection group at 18 h (P = 0.048) and to the ileum at 12 h (P = 0.049), and lower to the skin at 18 h (P = 0.015). In conclusion, the results indicate that multiple versus single microsphere injections induced no or negligible alterations during ovine sepsis. This finding may help reduce the quantity of animals needed in future experiments.

Dose effects of chronically infused nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester on anabolic response and arginine metabolism in rats with subacute peritonitis

Nitric oxide synthase (NOS) inhibitors alleviate the adverse effects of nitric oxide (NO) overproduction that occurs during peritonitis, a clinical condition that is accompanied by arginine deficiency. However, the variations in the disease severity and the dosage, route, and period of NOS inhibitor administration are debatable. Therefore, we investigated the dose effects of chronically infused NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) on the anabolism, inflammatory responses, and arginine metabolism in parenterally fed rats with cecal puncture-induced subacute peritonitis. Male Wistar rats were divided into 4 groups and were administered total parenteral nutrition solutions with 0, 5 (low dose), 25 (medium dose), or 50 (high dose) mg·kg(-1)·d(-1) of L-NAME for 7 d. Sham-operated rats administered total parenteral nutrition solution and normal healthy rats fed chow diet were also included. Our results showed that parenteral infusion significantly decreased body weight gain and plasma citrulline concentrations. In rats with subacute peritonitis, the parenteral infusion-induced increases in circulating white blood cells and NO were significantly decreased, whereas the decrease in serum albumin levels was significantly increased. Rats with subacute peritonitis that were administered chronic infusion of L-NAME had a significantly reduced nitrogen balance. In addition, rats administered the medium dose of L-NAME had significantly increased plasma arginine, ornithine, glutamate, and proline. In conclusion, chronic infusion of NOS inhibitors may not alter systemic NO homeostasis and inflammatory response but may facilitate the production of arginine-associated amino acids and nitrogen excretion in cases of subacute peritonitis.

Role of different nitric oxide synthase isoforms in a murine model of acute lung injury and sepsis

Excessive production of nitric oxide (NO) by NO synthase (NOS) with subsequent formation of peroxynitrite and poly(adenosine diphosphate ribose) is critically implemented in the pathophysiology of acute lung injury and sepsis. To elucidate the roles of different isoforms of NOS, we tested the effects of non-selective NOS inhibition and neuronal NOS (nNOS)- and inducible NOS (iNOS)-gene deficiency on the pulmonary oxidative and nitrosative stress reaction in a murine sepsis model. The injury was induced by four sets of cotton smoke using an inhalation chamber and subsequent intranasal administration of live Pseudomonas aeruginosa (3.2x10(7) colony-forming units). In wild type mice, the injury was associated with excessive releases of pro-inflammatory cytokines in the plasma, enhanced neutrophil accumulation, increased lipid peroxidation, and excessive formation of reactive nitrogen species and vascular endothelial growth factor in the lung. Both nNOS- and iNOS-gene deficiency led to significantly reduced oxidative and nitrosative stress markers in the lung, but failed to significantly improve survival. Treatment with a non-selective NOS inhibitor failed to reduce the oxidative and nitrosative stress reaction to the same extent and even tended to increase mortality. In conclusion, the current study demonstrates that both nNOS and iNOS are partially responsible for the pulmonary oxidative and nitrosative stress reaction in this model. Future studies should investigate the effects of specific pharmacological inhibition of nNOS and iNOS at different time points during the disease process.

Combined neuronal and inducible nitric oxide synthase inhibition in ovine acute lung injury

OBJECTIVE

Acute lung injury with subsequent pneumonia and sepsis represents a major cause of morbidity and mortality in thermally injured patients. Production of nitric oxide by the neuronal and inducible nitric oxide synthase may be critically involved in the pathophysiology of the disease process at different time points, and thus specific inhibition at different times may represent an effective treatment regimen.

DESIGN

Prospective, controlled, randomized trial.

SETTING

University research laboratory.

SUBJECTS

Eighteen chronically instrumented, adult, female sheep.

INTERVENTIONS

Following baseline measurements, the animals were allocated to either sham-injured, nontreated controls (sham), injured, nontreated controls (control), or injured animals treated with continuous infusion of 7-nitroindazole, a specific neuronal nitric oxide synthase inhibitor, during the first 12 hrs postinjury and infusion of BBS-2, a specific inducible nitric oxide synthase inhibitor, during the next 12 hrs. Injury was induced by 48 breaths of cotton smoke and subsequent instillation of Pseudomonas aeruginosa into the lungs. All sheep were mechanically ventilated and fluid resuscitated for the entire duration of the 24-hr experiment.

MEASUREMENTS AND MAIN RESULTS

The injury induced severe pulmonary dysfunction, which was associated with increases in lung edema formation, airway obstruction, and vascular endothelial growth factor, 3-nitrotyrosine, and poly(adenosine diphosphate ribose) expression in lung tissue. The treatment reduced the degree of airway obstruction and improved pulmonary gas exchange, whereas the development of lung edema was not affected. The increases in lung tissue vascular endothelial growth factor, 3-nitrotyrosine, and poly(ribose) expression were attenuated by the treatment.

CONCLUSIONS

The combination of early neuronal nitric oxide synthase and delayed inducible nitric oxide synthase inhibition shows potential benefit in ovine acute lung injury by reducing nitrosative stress in the lung and limiting the degree of airway obstruction.

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.

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.

San-Huang-Xie-Xin-Tang reduces lipopolysaccharides-induced hypotension and inflammatory mediators

San-Huang-Xie-Xin-Tang (SHXT) is a traditional Chinese medicinal formula containing Coptidis rhizoma, Scutellariae radix and Rhei rhizoma. The present study aimed to determine the preventive effects of standardized SHXT on lipopolysaccharides (LPS)-induced arterial hypotension, protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), cytokines formation and prostaglandin E2 (PGE2) production. LPS-induced activation of iNOS has been recognized to increase cytokines and nitric oxide, some of them play predominant roles in sepsis. Intravenous injection of LPS (10 mg/kg) caused a marked decrease of the mean arterial pressure in normotensive rats. However, the LPS-induced arterial hypotension was inhibited by SHXT (0.01 and 0.03 g/kg), when it was given 30 min before LPS. Moreover, plasma level of cytokines and PGE2 were lowered by SHXT. In RAW 264.7 cells, SHXT (20-200 microg/ml) dose-dependently inhibited LPS (1 microg/ml)-induced iNOS and COX-2 expression, and it also significantly decreased LPS-induced cytokines in a dose-dependent manner. In conclusion, our data suggest that SHXT prevented LPS-induced arterial hypotension, which might be mediated through its inhibition activities on the expression of iNOS and COX-2, cytokines formation and PGE2 production. Therefore, its protection activity against LPS-induced arterial hypotension and inflammatory mediators release might be beneficial in the treatment of endotoxin shock and/or associated inflammation.

Role of peroxisome proliferator-activated receptor-gamma in the protection afforded by 15-deoxydelta12,14 prostaglandin J2 against the multiple organ failure caused by endotoxin

OBJECTIVE

The cyclopentenone prostaglandin 15-deoxydelta-prostaglandin J2 (15 d-PGJ2) exerts potent anti-inflammatory effects in vivo, which are in part due to the activation of peroxisome proliferator-activated receptor (PPAR)-gamma. Here we investigate the effects of 15 d-PGJ2 on the multiple organ injury/dysfunction associated with severe endotoxemia.

DESIGN

Prospective, randomized study.

SETTING

University-based research laboratory.

SUBJECTS

Seventy anesthetized male Wistar rats.

INTERVENTIONS

Rats received either Escherichia coli lipopolysaccharide (endotoxin, 6 mg/kg intravenously) or vehicle (saline, 1 mL/kg intravenously). 15 d-PGJ2 (0.3 mg/kg intravenously) or vehicle (10% dimethyl sulfoxide) was administered 30 mins before endotoxin. The selective PPAR-gamma antagonist GW9662 (0.3 mg/kg intravenously) or its vehicle (10% dimethyl sulfoxide) was given 45 mins before endotoxin.

MEASUREMENTS AND MAIN RESULTS

Endotoxemia for 6 hrs increased serum concentrations of creatinine (indicator of renal dysfunction), aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, bilirubin (markers for hepatic injury and dysfunction), lipase (indicator of pancreatic injury), and creatine kinase (an indicator of neuromuscular skeletal muscle or cardiac injury). The potent PPAR-gamma agonist 15 d-PGJ2 attenuated the increases in the serum concentrations of these variables, indicating a protective effect of 15 d-PGJ2 against the multiple organ injury/dysfunction caused by endotoxin. The specific PPAR-gamma antagonist GW9662 reduced the protective effects afforded by 15 d-PGJ2. 15 d-PGJ2 did not affect the biphasic decrease in blood pressure or the increase in heart rate caused by endotoxemia.

CONCLUSIONS

The potent PPAR-gamma agonist 15 d-PGJ2 reduces the multiple organ injury and dysfunction, but not the hypotension, caused by endotoxin in the rat. The mechanisms of the protective effect of this cyclopentenone prostaglandin are--at least in part--PPAR-gamma dependent, as the protection afforded by 15 d-PGJ2 was reduced by the PPAR-gamma antagonist GW9662. We propose that 15 d-PGJ2 or other ligands for PPAR-gamma may be useful in treating organ injury associated with endotoxic shock.

Effects of titrated arginine vasopressin on hemodynamic variables and oxygen transport in healthy and endotoxemic sheep

OBJECTIVE

To determine the effects of titrated arginine vasopressin (AVP) alone or in combination with norepinephrine (NE) on hemodynamics and oxygen transport in healthy and endotoxemic sheep.

DESIGN

Prospective controlled trial.

SETTING

University research laboratory.

SUBJECTS

Six adult ewes.

INTERVENTIONS

Healthy sheep received AVP as a titrated infusion, initiated with 0.6 units/hr and increased by 0.6 units/hr every 15 mins, either until mean arterial pressure was increased by 20 mm Hg vs. baseline or a maximum of 3.6 units/hr was administered. After 90 mins, AVP infusion was continued with the investigated dosage, and NE (0.2 microg x kg(-1) x min(-1)) was also infused for 90 mins. After a 24-hr period of recovery, endotoxemia was induced and maintained (Salmonella typhosa endotoxin, 10 ng x kg(-1) x min(-1)) in the same sheep for the next 19 hrs. After 16 hrs of endotoxemia, AVP and NE were administered as described previously.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics were obtained at baseline, every 15 mins during the titration period, and 60 and 90 mins after additional NE infusion. Variables of oxygen transport were calculated before and after the titration period. In healthy and endotoxemic sheep, AVP reduced heart rate and cardiac index (p <.001) and compromised oxygen delivery (p <.001) and oxygen consumption (healthy sheep, p =.003; endotoxemic sheep, p <.001). Vasopressin infusion did not alter mean pulmonary arterial pressure but increased pulmonary vascular resistance index in both groups (p <.001). Additional infusion of NE further augmented mean arterial pressure and increased cardiac index during endotoxemia (p <.001). This was accompanied by an increase in oxygen delivery and consumption (p <.05 each).

CONCLUSIONS

During ovine endotoxemia, AVP decreased cardiac index, compromised oxygen delivery, and increased pulmonary vascular resistance index. These side effects may limit its use as a sole vasopressor during sepsis. Potentially, a simultaneous infusion of AVP and NE could represent a useful therapeutic option.

Cerebral blood flow is not altered in sheep with Pseudomonas aeruginosa sepsis treated with norepinephrine or nitric oxide synthase inhibition

The origin of cerebral dysfunction in patients with sepsis is still unclear. However, altered cerebral perfusion may play an important role in its pathogenesis. Using an established, chronic model of hyperdynamic ovine sepsis, we examined cerebral perfusion in 20 sheep subjected to a continuous infusion of live Pseudomonas aeruginosa. After 24 h of sepsis, the hypotensive sheep (reduction in mean arterial blood pressure by 16%; P < 0.05) received the nitric oxide synthase inhibitor N(G)-mono-methyl-L-arginine (L-NMMA; 7 mg. kg(-1). h(-1); n = 7), norepinephrine (NE; n = 7), or normal saline (control; n = 6). NE infusion was individually targeted to achieve the same increase in mean arterial blood pressure as that observed in matched sheep of the L-NMMA group. Regional perfusion was measured by using colored microspheres. Although L-NMMA caused a significant increase in systemic vascular resistance index (1167 +/- 104 versus 793 +/- 59 dyne. cm(-5). m(2); P < 0.05), it caused a change neither in cerebrovascular resistance nor in cerebral blood flow. When related to systemic blood flow, a redistribution of blood flow to the brain became obvious. The NE-associated increase in systemic blood pressure (98 +/- 5 versus 83 +/- 5; P < 0.05) was accompanied by an increase in cardiac output (7.8 +/- 0.5 versus 6.7 +/- 0.6; P < 0.05) and, hence, systemic perfusion. However, blood flow to the brain remained unaffected. Although detrimental vasoconstrictive effects of NE and L-NMMA, including cerebral hypoperfusion, are discussed, neither drug had any effect on cerebral perfusion during experimental hyperdynamic sepsis.

IMPLICATIONS

Cerebral dysfunction is often found in septic patients. In this regard, it is debated whether vasopressor drugs, such as norepinephrine and L(G)-mono-methyl-L-arginine, have harmful effects on the cerebral circulation. During experimental hyperdynamic sepsis, however, neither drug altered cerebral vascular resistance or cerebral blood flow.

Bench-to-bedside review: microvascular dysfunction in sepsis--hemodynamics, oxygen transport, and nitric oxide

The microcirculation is a complex and integrated system that supplies and distributes oxygen throughout the tissues. The red blood cell (RBC) facilitates convective oxygen transport via co-operative binding with hemoglobin. In the microcirculation oxygen diffuses from the RBC into neighboring tissues, where it is consumed by mitochondria. Evidence suggests that the RBC acts as deliverer of oxygen and 'sensor' of local oxygen gradients. Within vascular beds RBCs are distributed actively by arteriolar tone and passively by rheologic factors, including vessel geometry and RBC deformability. Microvascular oxygen transport is determined by microvascular geometry, hemodynamics, and RBC hemoglobin oxygen saturation. Sepsis causes abnormal microvascular oxygen transport as significant numbers of capillaries stop flowing and the microcirculation fails to compensate for decreased functional capillary density. The resulting maldistribution of RBC flow results in a mismatch of oxygen delivery with oxygen demand that affects both critical oxygen delivery and oxygen extraction ratio. Nitric oxide (NO) maintains microvascular homeostasis by regulating arteriolar tone, RBC deformability, leukocyte and platelet adhesion to endothelial cells, and blood volume. NO also regulates mitochondrial respiration. During sepsis, NO over-production mediates systemic hypotension and microvascular reactivity, and is seemingly protective of microvascular blood flow.

Cyclooxygenase-2 inhibition attenuates lipopolysaccharide-induced cardiovascular failure

The present study aimed to determine the relevance of cyclooxygenase-2 (COX-2)-derived prostanoids for the adverse effects of lipopolysaccharides (LPSs) on cardiovascular function. For this goal, male Sprague-Dawley rats received a single intravenous dose of LPS (10 mg/kg) and were treated with different cyclooxygenase inhibitors. Injection of LPS caused a marked decrease of systolic arterial pressure, from 128 to 79 mm Hg, and a concomitant increase of heart rate, from 380 to 530 minutes(-1). Both the decrease of systemic arterial pressure and the increase of heart rate induced by LPS were almost absent if the animals also received the COX-2 blocker rofecoxib (20 mg/kg), regardless whether the drug was given 1 hour before or 1 hour after LPS. Although plasma and organ levels of prostanoids were lowered by rofecoxib, the characteristic LPS-induced increases of NO synthase II and COX-2 gene expression, as well as of plasma and tissue nitrate/nitrite concentrations, were not affected by rofecoxib. Although rofecoxib treatment did also not change LPS-induced tissue cytokine concentrations, it markedly improved LPS-induced liver damage, as indicated by the decrease of transaminases. Moreover, the overall well-being of the LPS-injected animals improved on concomitant treatment with the COX-2 inhibitor. Taken together, our data suggest that COX-2-derived prostanoids are major mediators for the detrimental effects of LPS on cardiovascular and organ function.

Nitric oxide scavenging, alone or with nitric oxide synthesis inhibition, modulates vascular hyporeactivity in rats with intraperitoneal sepsis

Elevated levels of nitric oxide (NO) may be a primary cause of the vascular hyporeactivity (vasoplesia) and refractory hypotension in sepsis. This study was initiated to determine the efficacy of NO scavenging with acellular hemoglobin (Hb) solution in modulating sepsis-mediated vasoplesia. Male Sprague Dawley rats were subjected to sepsis by cecal ligation and puncture (CLP). Twenty-four hours post-CLP, the animals were randomly assigned to one of four groups (n = 5-6 each) and given an intravenous injection of 0.5 mL bovine serum albumin (BSA; 5 g/dL), 0.5 mL human Hb (7g/dL), 50 microL Nomega-nitro L-arginine methyl ester (NAME; 1 M), or both Hb and NAME. Blood pressure (BP), cardiac output, systemic vascular resistance, and vascular reactivity (VR) to norepinephrine (NE; 40 ng/Kg) were assessed before and after an experimental treatment. In some animals, inducible NO synthase (iNOS) mRNA expression was assessed in selected tissue samples harvested at the conclusion of experiment using a reverse transcription-polymerase chain reaction (RT-PCR) method. Treatment with Hb, NAME, or NAME + Hb elicited a significant improvement in mean BP and VR compared with the control (BSA) group (P < 0.05, analysis of variance and Neuman-Keuls tests). Tissue samples from 24-h CLP rats clearly exhibited iNOS gene expression; higher iNOS gene expression in the intestine compared with aorta suggests that the intestine may be a major source of the elevated NO level in this model. In conclusion, NO scavenging with Hb, alone, or in combination with NO synthesis inhibition, appears to be effective in modulating sepsis-mediated vascular hyporeactivity and may reduce complications associated with global NO synthesis inhibition.

Nitric oxide scavenging modulates an experimental vasoplesia in-vitro

Endogenous overproduction of nitric oxide (NO) is believed to be a primary cause of refractory hypotension in septic shock. Under this condition, effectiveness of vasopressors is diminished due to hyporeactivity of blood vessels, a condition termed as vasoplesia. Effective reduction of NO levels should alleviate the condition. In this study, we investigated whether NO scavenging could modulate the endotoxin mediated vasoplesia in-vitro. Further, we explored whether NO scavenging in combination with a moderate NO synthase (NOS) inhibition would also be effective in modulating NO mediated vasoplesia. Experimental vasoplesia was produced in-vitro by incubating isolated rat thoracic aortic rings with lipopolysaccharide (LPS). Vessel rings were then treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; a NOS inhibitor), human hemoglobin (Hb; a NO scavenger), or both L-NAME and Hb. Vascular reactivity was assessed by measuring vessel ring isometric tension changes to norepinephrine (NE) doses; the median effective doses (logEC50) of NE before and after each experimental treatment were compared. Following a 6-hour LPS treatment, vascular reactivity logEC50 values for NE were significantly increased compared with control vessel rings incubated without LPS. Treatment with either L-NAME alone or Hb alone significantly improved the vessel ring reactivity to NE. When both L-NAME and Hb were used concomitantly, vascular reactivity was also significantly improved. These results indicate that NO scavenging with Hb is as effective as NO synthesis inhibition with NAME in modulating the endotoxin induced vasoplesia. In conclusion, NO scavenging, alone or in combination with a moderate NOS inhibition, may render an alternative therapeutic approach to NOS synthesis inhibition in modulating the vasoplesia in septic shock.

The role of adrenomedullin in producing differential hemodynamic responses during sepsis

Although the hemodynamic response to polymicrobial sepsis is characterized by an early, hyperdynamic phase followed by a late, hypodynamic phase, the factors responsible for producing the transition from the hyperdynamic to the hypodynamic stage are not fully understood. The failure to recognize or prevent this transition may lead to progressive deteriorations in cell and organ functions and ultimately result in multiple organ failure. Despite the fact that several vasoactive mediators (i.e., nitric oxide, prostacyclin, calcitonin gene-related peptide) have been implicated in producing cardiovascular alterations during sepsis, recent studies have indicated that adrenomedullin (AM), a novel vasodilatory peptide, plays an important role in initiating the hyperdynamic response during the early stage of polymicrobial sepsis. In addition, the reduced vascular responsiveness appears to be responsible for producing the transition from the early, hyperdynamic phase to the late, hypodynamic phase of sepsis. Moreover, modulation of AM vascular responsiveness reduces sepsis-induced mortality. In this review the physiological effects of AM, mechanisms of its action, and regulation of its production under various pathophysiological conditions will be discussed. Furthermore, the role of AM in producing the biphasic hemodynamic responses observed during polymicrobial sepsis and approaches for pharmacologically modulating vascular responsiveness and hemodynamic stability under such conditions will be described.

Hemodynamic and cardiovascular effects of nitric oxide modulation in the therapy of septic shock

Nitric oxide synthase (NOS) of the inducible subtype (iNOS) plays a pivotal role in vasodilation associated with sepsis. Various biochemical pathways are involved, revealing targets for inhibiting the consequence of iNOS activation. Interactions of transcription factors, inducers, cofactors, and regulators of iNOS are important in understanding the development of iNOS inhibitors. Inhibition through L-arginine analogs, depletion of arginine, inhibition of cofactors, modulating gene transcription, and scavenging nitric oxide have been studied. Human studies were conducted only with nonselective L-arginine analogs. Reduction of mortality from sepsis was not reported. It is anticipated that iNOS-specific compounds will be clinically useful. The focus of future human trials will be on these agents. Although ideal therapy for treating vasodilation from sepsis is not available, research into the pathophysiology of NOS in sepsis clarified the complexities surrounding this therapeutic dilemma.

Physiologic role of nitric oxide in the maintenance of uterine quiescence in nonpregnant and pregnant sheep

OBJECTIVE

This study evaluated the role of nitric oxide in the maintenance of uterine quiescence in nonpregnant and pregnant ewes.

STUDY DESIGN

Sixteen ovariectomized nonpregnant and 10 pregnant (115 days' gestation) chronically instrumented ewes were studied. Uterine contractility was assessed by electromyography and intrauterine pressure recordings. Nitric oxide synthase inhibition was induced with nitro-L -arginine methyl ester or aminoguanidine (4. 5 mg/kg per hour) given during estrogen replacement with 17beta-estradiol (100 microg/d) or in late gestation. In the pregnant group we evaluated the ability of nitric oxide synthase inhibition to alter the responsiveness to oxytocin-induced uterine contractility. Blood pressure and common internal iliac artery blood flow were assessed to confirm nitric oxide synthase inhibition. In addition, the effects of the nitric oxide donor nitroglycerin and the cyclooxygenase inhibitor indomethacin were studied in nonpregnant sheep. The effect of nitric oxide in vitro on myometrial spontaneous and induced contractions was also studied.

RESULTS

In nonpregnant estrogen-replaced sheep, nitric oxide synthase inhibition and nitroglycerin administration did not alter uterine contractility, despite significant changes in blood pressure. In contrast, indomethacin decreased electromyographic results to 70% of baseline after 1 hour and 47% after 2 hours. In pregnant ewes nitric oxide synthase inhibition failed to alter uterine contractility in response to oxytocin. These findings are in contrast to results of the in vitro study in which nitric oxide was shown to relax sheep myometrium.

CONCLUSION

The absence of significant effects of nitric oxide synthase inhibition and nitric oxide donors on uterine contractility in vivo suggests that nitric oxide does not play a physiologic role in the regulation of uterine contractility in nonpregnant or pregnant ewes.

Microcirculatory dysfunction in sepsis: a pathogenetic basis for therapy?

Sepsis is a frequent complication of multiple organ dysfunction syndrome and remains a major problem of intensive care medicine. It is also a common factor in the final cause of death in hospital populations. Clinical observations, assisted by invasive monitoring techniques as well as pathological-anatomical studies, clearly indicate that microcirculatory dysfunction lies at the centre of sepsis pathogenesis. Numerous animal models, from rodents to primates, many of which employ bacteria or their toxins, especially endotoxins, have helped to shed light on the pathomechanisms leading to this dysregulation in the peripheral circulation. Among these are activation of humoral and cellular inflammatory mediator systems, with special emphasis on neutrophil-endothelial interactions, affecting endothelial barrier function and vasoregulation and ultimately leading to severely perturbed oxygen transport and utilization. In vitro studies have provided more insight into the molecular mechanisms involved in this microcirculatory dysfunction, although much more attention must be directed towards microvascular endothelial cells and the role of heterogeneity of response in various vascular beds. These experimental data must in turn be validated by comparing with the human in situ situation, both clinical and morphological. This review aims at a critical appraisal of the clinical and experimental evidence for sepsis-induced dysregulation of the microcirculation and how knowledge of the underlying cellular and molecular pathology could be used to make therapy more rational and effective. To date, therapeutic approaches, such as anti-cytokine and anti-oxidant regimens, which have been highly successful in experimental models, have failed to demonstrate clinical efficacy. Newer approaches, such as targeting the coagulation system, nitric oxide synthesis or intracellular signal transduction, are also discussed. The necessity to focus on the role of anti-inflammatory mediators, as well as the pathogenetic significance of important molecular groups, such as the heat shock proteins, which until now have been given scant attention, will be stressed.