Nitric Oxide Synthase Inhibition Restores Vasopressor Effects of Norepinephrine in Ovine Hyperdynamic Sepsis

Dose-related effects of norepinephrine on early-stage endotoxemic shock in a swine model

Background

The benefits of early use of norepinephrine in endotoxemic shock remain unknown. We aimed to elucidate the effects of different doses of norepinephrine in early-stage endotoxemic shock using a clinically relevant large animal model.

Methods

Vasodilatory shock was induced by endotoxin bolus in 30 Bama suckling pigs. Treatment included fluid resuscitation and administration of different doses of norepinephrine, to induce return to baseline mean arterial pressure (MAP). Fluid management, hemodynamic, microcirculation, inflammation, and organ function variables were monitored. All animals were supported for 6 h after endotoxemic shock.

Results

Infused fluid volume decreased with increasing norepinephrine dose. Return to baseline MAP was achieved more frequently with doses of 0.8 µg/kg/min and 1.6 µg/kg/min (P <0.01). At the end of the shock resuscitation period, cardiac index was higher in pigs treated with 0.8 µg/kg/min norepinephrine (P <0.01), while systemic vascular resistance was higher in those receiving 0.4 µg/kg/min (P <0.01). Extravascular lung water level and degree of organ edema were higher in animals administered no or 0.2 µg/kg/min norepinephrine (P <0.01), while the percentage of perfused small vessel density (PSVD) was higher in those receiving 0.8 µg/kg/min (P <0.05) and serum lactate was higher in the groups administered no and 1.6 µg/kg/min norepinephrine (P <0.01).

Conclusions

The impact of norepinephrine on the macro- and micro-circulation in early-stage endotoxemic shock is dose-dependent, with very low and very high doses resulting in detrimental effects. Only an appropriate norepinephrine dose was associated with improved tissue perfusion and organ function.

Somatostatin infusion increases intestinal ischemia and does not improve vasoconstrictor response to norepinephrine in ovine endotoxemia

Hemodynamic support of patients with septic shock is often complicated by a tachyphylaxis against exogenous catecholamines. Because an increase in somatotropic hormones may play a pivotal role in the regulation of the inflammatory response to endotoxin, intravenous supplementation of the neuroendocrine hormone somatostatin (SOMA) may attenuate hemodynamic dysfunction resulting from endotoxemia. The objective of the present study was to assess the short-term effects of SOMA alone and in combination with norepinephrine (NE) on cardiopulmonary hemodynamics, global oxygen transport, plasma nitrate/nitrite levels, and intestinal integrity compared with single NE therapy in ovine endotoxemia. After a baseline measurement in healthy sheep (n = 16) had been performed, Salmonella typhosa endotoxin was centrally infused (10 ng x kg(-1) x min(-1)) to induce a hypotensive-hyperdynamic circulation using an established protocol. Animals surviving 16 h of endotoxemia were randomly assigned to one of the two groups (each n = 6). Sheep allocated to the SOMA + NE group received SOMA as a loading dose of 10.5 microg x kg(-1) x min(-1) for 1 h, followed by a continuous infusion of 3.5 microg x kg(-1) x min(-1) for the next 2 h. After the SOMA loading dose had been given, NE was concurrently infused (0.3 microg x kg(-1) x min(-1)) for 2 h. In the NE group (control), NE (0.3 microg x kg(-1) x min(-1)) was continuously infused for 3 h. Endotoxemia caused a decrease in MAP and systemic vascular resistance index in both groups, but to a greater extent in the NE group. Arterial hypotension persisted despite administration of the study drugs. Infusion of SOMA alone and in combination with NE did not significantly increase systemic vascular resistance index. Neither SOMA nor NE infusion alone affected pulmonary vasoregulation. Plasma nitrate/nitrite levels did not differ between groups. However, combined infusion of SOMA and NE significantly increased arterial lactate concentrations, oxygen consumption index, and oxygen extraction rate (P < 0.05) and aggravated ileal mucosal injury. In conclusion, short-term treatment with SOMA failed to attenuate cardiocirculatory shock resulting from endotoxemia and did not improve vasopressor response to NE. In addition, combined SOMA and NE therapy resulted in intestinal injury. Therefore, SOMA does not seem to represent a therapeutic option to treat arterial hypotension resulting from sepsis and systemic inflammatory response syndrome.

Hemodynamic effects of titrated norepinephrine in healthy versus endotoxemic sheep

In patients with sepsis and systemic inflammatory response syndrome, hemodynamic support is often complicated by a vascular hyporesponsiveness to exogenously administered norepinephrine. Although norepinephrine tachyphylaxis represents a significant clinical problem, the relationship between norepinephrine dosages and mean arterial pressure (MAP) in the presence of systemic inflammation is still not fully understood. This study was, therefore, designed as a prospective, controlled laboratory trial to elucidate the hemodynamic response to incremental norepinephrine doses in healthy and endotoxemic sheep. ANOVA demonstrated that a significantly higher mean infusion rate of norepinephrine was needed to increase MAP by 20 mmHg in endotoxemic versus healthy control sheep (P = 0.007). Whereas the goal-MAP was reached in 100% of healthy controls, it was achieved in only 80% during endotoxemia. Cardiac index increased significantly in healthy, but not in endotoxemic, sheep. Our findings confirm the presence of vascular hyporesponsiveness to norepinephrine in endotoxemia. In addition, this study demonstrates that the presence of systemic inflammation leads to an early hyporesponsiveness against norepinephrine which was caused by a drug-independent mechanism rather than a tachyphylaxis due to long-term administration of norepinephrine.

Short-term effects of glipizide (an adenosine triphosphate-sensitive potassium channel inhibitor) on cardiopulmonary hemodynamics and global oxygen transport in healthy and endotoxemic sheep

In severe sepsis and septic shock, hemodynamic support is often complicated by a tachyphylaxis against exogenous catecholamines. Because activation of adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels plays a pivotal role in the pathogenesis of hyperdynamic vasodilatory shock, we hypothesized that it may be beneficial to administer a specific K(ATP) channel inhibitor to prevent, or at least attenuate, hemodynamic dysfunction in sepsis. The present study was designed as a prospective and controlled laboratory experiment to elucidate the short-term effects of glipizide, a specific K(ATP) channel inhibitor, on cardiopulmonary hemodynamics and global oxygen transport in healthy sheep and sheep with endotoxemia. Ten adult ewes were anesthetized and operatively instrumented with a pulmonary artery, a femoral artery, and a foley catheter. After 24 h of recovery, healthy sheep received glipizide as a bolus infusion (4 mg/kg over 15 min). After 24 h of recovery, a continuous infusion of endotoxin (Salmonella typhosa, 10 ng.kg.(-1)min) was started in the same sheep and administered for the next 17 h. After 16 h of endotoxemia, glipizide was given as described above. Administration of glipizide was followed by a transient, but significant, increase in mean arterial pressure in both healthy controls (95 +/- 3 mmHg vs. 101 +/- 2 mmHg, P < 0.05) and sheep with endotoxemia (86 +/- 3 mmHg vs. 93 +/- 3 mmHg, P < 0.05). However, the increase in mean arterial pressure was longer lasting in ewes with endotoxemia. Cardiac index, oxygen delivery index, arterial lactate concentrations, and arterial pH were not significantly affected by glipizide. Therefore, administration of glipizide may represent a beneficial therapeutic option to treat arterial hypotension resulting from sepsis and systemic inflammatory response syndrome. Additional studies are required to determine the effects of continuous infusion of glipizide in the presence of systemic inflammation.

Is spontaneous bacterial peritonitis an inducer of vasopressin analogue side-effects? A case report

In recent years, the use of vasopressin analogues in the treatment of hepatorenal syndrome has become an effective therapeutic strategy leading to improved survival and often allowing the completion of liver transplantation. Terlipressin, in particular, has proven to be safe and effective. Due to the limited number of patients treated so far, it is, however, difficult to draw any definite conclusions on the optimal dosage and on the occurrence of side-effects in these patients. The case is reported of an ascitic cirrhotic patient who developed spontaneous bacterial peritonitis followed by a type-I hepatorenal syndrome. Treatment with terlipressin boluses (0.5 mg/4 h) associated with albumin infusion was then started. The course of the disease was monitored by clinical and laboratory means. After 10 boluses of terlipressin, rectorrhagia and severe ischaemic complications involving the skin of the abdomen, lower limbs, scrotus, and penis, occurred. These ischaemic complications improved after terlipressin withdrawal, while renal failure evolved leading to the patient's death. This case report shows that, in patients with type-I hepatorenal syndrome, the use of terlipressin, even at low dosages, may induce life-threatening ischaemic complications and, moreover, suggests that the recent occurrence of spontaneous bacterial peritonitis, even if properly treated, may significantly increase the risk of major ischaemic complications.

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.

Norepinephrine in septic patients--friend or foe?

Norepinephrine (NE) is mostly used to treat severe hypotension. However, NE has potentially adverse vasoconstrictive effects on regional vascular beds of kidney, liver, and gut, with a potential for ensuing organ dysfunction. NE therefore is considered as a last reserve in otherwise refractory hypotension. During sepsis, a loss of catecholamine responsiveness occurs that is often interpreted as down-regulation of catecholamine receptors. Therefore, the doses of NE needed to maintain or restore blood pressure may be extremely high. Surprisingly, no adverse vasoconstriction with subsequent hypoperfusion occurs during sepsis, despite the high doses of NE administered. Instead, NE rather causes an increase in blood flow and oxygen delivery.

Hemodynamic effects of exogenous adrenomedullin in healthy and endotoxemic sheep

Adrenomedullin (AM) is a vasodilatory peptide hormone, playing a key role in the regulation of cardiovascular homeostasis. In view of the circulatory failure in sepsis, it is still debated as to whether the occurrence of vascular hyporeactivity against AM plays a causative or protective role. This study was designed as a prospective, controlled trial to elucidate the hemodynamic response following a titrating infusion of human AM in healthy and endotoxemic sheep. ANOVA demonstrated that AM infusion produced hypotension and tachycardia, and increased cardiac index in a dose-dependent manner, both in healthy and endotoxemic sheep. In addition, AM application reduced pulmonary vascular resistance index in ovine endotoxemia (P=0.02). These findings confirm that AM produces a hyperdynamic circulation, in the presence and absence of systemic inflammation. Further, exogenous AM could possibly be a useful adjunct in the common setting of sepsis-associated pulmonary hypertension.

Hemodynamic effects of terlipressin (a synthetic analog of vasopressin) in healthy and endotoxemic sheep

OBJECTIVE

Hypotension, vasodilation, and vasoplegia are characteristic signs of septic shock. The vasoconstrictive response to catecholamines typically is reduced. A decreased vasopressive effect of catecholamines can be observed in the late phase of hemorrhagic shock. Interestingly, an unaltered vasopressive response to vasopressin can be demonstrated in hemorrhagic shock. In this study, we investigated the vasoconstrictive response to an agonist of the vasopressin receptor, terlipressin, in healthy sheep as well as in ovine hyperdynamic endotoxemia.

DESIGN

Prospective controlled trial.

SETTING

University research laboratory.

SUBJECTS

Six female adult sheep.

INTERVENTIONS

Healthy sheep, instrumented for chronic study, received terlipressin (15 microg/kg) as a bolus; 30 mins later, norepinephrine was continuously given for 30 mins. Three hours later, a continuous infusion of endotoxin (Salmonella typhosa, 10 ng x kg(-1) x min(-1)) was started in the same sheep and given for the next 23 hrs. After 20 hrs of endotoxemia, terlipressin and norepinephrine were given as described previously.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic parameters were measured before and 30 mins after application of terlipressin and after 30 mins of continuous infusion of norepinephrine. Terlipressin significantly increased systemic vascular resistance index in healthy and endotoxemic sheep (p <.05). The increase was higher in endotoxemic compared with healthy animals (p <.05). Only during endotoxemia, terlipressin increased pulmonary vascular resistance index. This was accompanied by a significant decrease in cardiac index, whereas mean pulmonary arterial pressure did not change after application of terlipressin. Additional treatment with norepinephrine did not further increase systemic vascular resistance index or pulmonary vascular resistance index.

CONCLUSIONS

Terlipressin reversed the hemodynamic changes in ovine endotoxemia. However, its pulmonary vasopressive effect might limit its therapeutic use in septic shock.

Alanyl-glutamine dipeptide does not affect hemodynamics despite a greater increase in myocardial heat shock protein 72 immunoreactivity in endotoxemic sheep

The possible beneficial effect of supplemental glutamine (Gln) in critically ill patients has been suggested to be mediated by the induction of the cytoprotective heat shock proteins (HSP)32 and HSP72. There is evidence that HSP72 and HSP32 have opposite effects on the hemodynamic situation during endotoxemia. Therefore, the effect of Gln supplementation on the cardiovascular system is not clear. We investigated the effect of alanyl-Gln (Ala-Gln) dipeptide on cardiovascular function in healthy and endotoxemic sheep. Ten sheep catheterized for chronic studies received Ala-Gln 700 mg/(kg x d) [equal to 470 mg/(kg x d)Gln] on 4 consecutive days, and 10 sheep received NaCl (9 g/L) as the control solution. On d 4, four sheep of each group were killed and myocardial samples were taken for immunohistochemistry. The remaining sheep received a continuous infusion of endotoxin [Salmonella typhosa, 10 ng/(kg x min)]. Hemodynamic parameters were measured before application of Ala-Gln or the control solution, and during endotoxemia. Myocardial HSP72 immunoreactivity was determined by immunohistochemistry. After 24 h of endotoxemia, the sheep exhibited a hyperdynamic circulation. No difference was found in the hemodynamic parameters between treatment and control group. Ala-Gln treated sheep had a greater increase in myocardial HSP72 immunoreactivity compared with controls after (P < 0.05) but not before endotoxemia. In summary, Ala-Gln increased HSP72 immunoreactivity after endotoxemia, but did not alter hemodynamic parameters. Thus, Ala-Gln supplementation does not seem to aggravate the hyperdynamic circulation in endotoxemic shock.

Adenosine and nitric oxide regulate regional vascular resistance via interdependent and independent mechanisms during sepsis

OBJECTIVE

Adenosine receptor blockade increases regional resting vascular resistance during sepsis. In healthy subjects, part of adenosine's actions are mediated via stimulation of nitric oxide synthase. Because nitric oxide synthase activity is thought to be a major contributor to altered vascular tone in sepsis, we tested the hypothesis that some of the nitric oxide-mediated resting regional resistance during sepsis is secondary to endogenous adenosine stimulation of nitric oxide synthase.

DESIGN

Prospective, randomized, controlled experiment.

SETTING

Shock-trauma and basic science laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Twenty-four hours after sepsis or sham induction, rats were separated into two groups (n = 6 to 10 in each group). Group 1 received a 10-min infusion of the adenosine antagonist 8-sulfophenyltheophylline (0.9 mg/kg x min) followed by a 10-min infusion of L-nitro-arginine-methyl ester (0.5 mg/kg x min). Group 2 similarly received L-nitro-arginine-methyl ester followed by 8-sulfophenyltheophylline in the presence of L-nitro-arginine-methyl ester.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic and blood flow measurements (microspheres) were made before infusions, 10 mins after the administration of each single-agent infusion, and 10 mins after combined-agent infusions were administered. No significant resistance alterations were observed in nonseptic rats. In septic rats, adenosine receptor blockade alone increased hepatosplanchnic and skeletal muscle vascular resistance, but no further increases were seen when L-nitro-arginine-methyl ester was added. Nitric oxide synthase inhibition alone increased hepatosplanchnic and skeletal muscle vascular resistances. When 8-sulfophenyltheophylline was added to the infusion, skeletal muscle vascular resistance increased significantly more than with L-nitro-arginine-methyl ester alone, but there were no further increases in hepatosplanchnic resistance. Renal and adipose vascular resistances increased with L-nitro-arginine-methyl ester infusions, and 8-sulfophenyltheophylline produced no effect.

CONCLUSIONS

During sepsis, nitric oxide caused resting vasodilation independent of adenosine in the renal and adipose vasculature. In the hepatosplanchnic circulation, there is reciprocal adenosine-nitric oxide interaction in maintaining resting regional resistance. Skeletal muscle displayed a dual adenosine-mediated (nitric oxide-independent) and nitric oxide-mediated (adenosine receptors required) interaction to regulate resting resistance during sepsis. These data indicate that in the hepatosplanchnic and skeletal muscle vasculature, all of the resting nitric oxide-mediated vasodilation is secondary to endogenous adenosine action, but in adipose and renal vasculature, resting nitric oxide mediated vasodilation is independent of adenosine. Endogenous adenosine also appears to play a significant role in determining resting skeletal muscle resistance that is independent of nitric oxide synthase during sepsis.

Norepinephrine and N(G)-monomethyl-L-arginine in hyperdynamic septic shock in pigs: effects on intestinal oxygen exchange and energy balance

OBJECTIVES

To compare the effects of norepinephrine (NOR) and the nonselective nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), on intestinal blood flow, oxygen exchange, and energy metabolism over 24 hrs of hyperdynamic, normotensive porcine endotoxic shock.

DESIGN

Prospective, randomized, experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Twenty-seven pigs were divided into three groups: seven animals received no vasopressor therapy (ETX) during endotoxic shock; ten animals were treated with NOR; and ten animals were treated with L-NMMA.

INTERVENTIONS

Pigs were anesthetized, mechanically ventilated, and instrumented. Eight hours later, endotoxic shock was initiated by an infusion of Escherichia coli lipopolysaccharide. Animals were resuscitated by hetastarch directed to maintain the intrathoracic blood volume and a mean arterial pressure (MAP) of >60 mm Hg. Twelve hours after the start of the endotoxin infusion, NOR or L-NMMA was administered for 12 hrs in the treatment groups to maintain a MAP at preshock levels.

MEASUREMENTS AND MAIN RESULTS

ETX caused a continuous fall in MAP, despite a sustained increase in the cardiac output achieved by fluid resuscitation. NOR maintained MAP at preshock levels because of a further rise in cardiac output, whereas hemodynamic stabilization during L-NMMA resulted from systemic vasoconstriction. NOR increased portal venous blood flow concomitant with decreased intestinal oxygen extraction, whereas L-NMMA influenced neither portal venous blood flow nor intestinal oxygen extraction. Mean capillary hemoglobin oxygen saturation of the ileal mucosa as well as the frequency distributions reflecting microcirculatory oxygen availability remained unchanged as well. Nevertheless, portal venous pH similarly decreased and portal venous lactate/pyruvate ratios increased in all three groups. The arterial-ileal mucosal PCO2 gap progressively increased in the ETX and L-NMMA groups, whereas NOR blunted this response.

CONCLUSIONS

Neither treatment could reverse the ETX-induced derangements of cellular energy metabolism as reflected by the increased portal venous lactate/pyruvate ratios. The NOR-induced attenuation of ileal mucosal acidosis was possibly caused by a different pattern of blood flow redistribution compared with L-NMMA.

Vascular hyporesponsiveness of the renal circulation during endotoxemia in anesthetized pigs

OBJECTIVE

To compare the vascular reactivity of the renal circulation in control and septic conditions.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Anesthetized pigs (n = 17).

INTERVENTIONS

Ten pigs received a continuous intravenous infusion of endotoxin from Escherichia coli (160 ng x kg(-1) x hr(-1)) during 18 hrs, whereas seven control animals received a saline infusion. To test the vascular reactivity, norepinephrine (NE) (1 microg x kg(-1)), acetylcholine (10 microg x kg(-1)), and sodium nitroprusside (10 microg x kg(-1)) were intravenously injected for 20 secs and changes of mean arterial pressure and renal blood flow were observed during the 200 secs after the drug administration. To compare the evolution of the vascular reactivity over time, three tests were performed 5 hrs, 11 hrs, and 17 hrs after initial endotoxin or saline administration.

MEASUREMENTS AND MAIN RESULTS

Endotoxin infusion induced a hypotensive and hypokinetic syndrome with renal hypoperfusion. The mean arterial pressure increase after NE injection and the mean arterial pressure decrease after acetylcholine and nitroprusside were lower in endotoxin than in control pigs. In the renal circulation, the increase of resistance after NE injection and the decrease of renal resistance after acetylcholine and nitroprusside injections were lower in endotoxin than in control pigs.

CONCLUSIONS

This study shows a hyporesponsiveness of the renal circulation to vasoactive agents during endotoxemia. Vasoconstriction to NE, endothelium-dependent as well as endothelium-independent relaxations are altered during endotoxemia but not abolished, and despite the continuous infusion of endotoxin for 18 hrs, no recovery was observed over time.

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.

Response of the septic vasculature to prolonged vasopressor therapy with N(omega)-monomethyl-L-arginine and epinephrine in canines

OBJECTIVE

To investigate the effect of blocking nitric oxide production on cardiovascular function and survival in canine septic shock treated with or without a conventional vasopressor.

DESIGN

Randomized, controlled trial.

SETTING

An animal research laboratory at the National Institutes of Health.

SUBJECTS

Sixty purpose-bred beagles.

INTERVENTIONS

Fibrin clots containing Escherichia coli were surgically placed into the peritoneal cavity. N(omega)-monomethyl-L-arginine (L-NMMA) 10 mg/kg followed by 0.5, 1.0, or 4.0 mg/kg/hr), epinephrine (1 microg/kg/min), both, or neither were infused for 24 hrs beginning 6 hrs after the onset of infection. All animals received fluid and antibiotic therapy.

MEASUREMENTS AND MAIN RESULTS

Serum nitric oxide metabolites, nitrite and nitrate, increased with infection (p = .024) and decreased with L-NMMA (p = .004, all doses combined). Myocardial nitric oxide synthase activity was ranked as follows: nonsurvivors > survivors > noninfected controls (p < .01). Other tissues examined showed the same pattern. L-NMMA produced sustained increases in systemic vascular resistance index and mean arterial pressure 9 and 24 hrs after the onset of infection (p < or = .04). Left ventricular ejection fraction was depressed by septic shock (p = .01) and further decreased by L-NMMA (p = .02). However, control and L-NMMA cardiac index values were similar (p > .4), perhaps because L-NMMA increased pulmonary artery occlusion pressure (p = .02). From 9 to 24 hrs, epinephrine, in the absence or presence of L-NMMA, blunted recovery of cardiac index (p < .02) and had a diminishing vasopressor effect (p = .05). Neither L-NMMA nor epinephrine, individually or combined, significantly altered survival rates at the doses investigated (p > or = .69).

CONCLUSIONS

The tested doses showed that nitric oxide production was inhibited by L-NMMA in canine septic shock, but mortality and myocardial depression were unaffected. These results suggest that if L-NMMA has a beneficial effect on survival rates in septic shock, it is small.

Detrimental effect of a non-selective nitric oxide synthase inhibitor on the energy state of the liver following acute endotoxemia in rabbits

BACKGROUND

The effect of nitric oxide synthase (NOS) inhibitors in septic shock is very controversial. It is known that the administration of NOS inhibitors to normal subjects itself increases pulmonary vascular resistance with a concomitant decrease of cardiac output. Therefore, the hypothesis was tested that the detrimental effects of a non-selective NOS inhibitor on liver energetics in a rodent model of endotoxemia are mediated by the adverse pulmonary circulatory effect of the drug itself.

METHODS

Twenty anesthetized rabbits were instrumented and two separate experiments (a magnetic resonance spectroscopic study and a hemodynamic study) were performed under similar conditions. Animals were assigned randomly to either a control group (group 1; animals received lipopolysaccharide (LPS) at a dose of 400 microg/kg alone) or a treatment group (group 2; animals received NG-nitro-L-arginine methyl ester (L-NAME) at a dose of 7.5 mg/kg, 75 min after administration of LPS).

RESULTS

In group 1, slight decreases in hepatic adenosine triphosphate (ATP) value were observed. In group 2, the decreases in ATP values were more prominent than those observed in group 1. LPS produced an acute drop in mean arterial pressure (MAP) with a concomitant increase in pulmonary vascular resistance (PVR) and a reduction in the cardiac output (CO) at 30 min after LPS. The administration of L-NAME caused a transient increase in MAP with a concomitant increase in systemic vascular resistance at 2 h after LPS. However, these changes in PVR and CO were more prominent than in group 1.

CONCLUSION

These results suggest that alterations within the pulmonary circulation may be a contributing factor which was responsible for the non-selective NOS inhibitor-induced acute hepatic energy derangement after LPS.