Cardiac effects of endothelin receptor antagonism in endotoxemic pigs

Myocardial depression in sepsis is frequently encountered clinically and contributes to morbidity and mortality. Increased plasma levels of endothelin-1 (ET-1) have been described in septic shock, and previous reports have shown beneficial effects on cardiovascular performance and survival in septic models using ET receptor antagonists. The aim of the current study was to investigate specific cardiac effects of ET receptor antagonism in endotoxicosis. Sixteen domestic pigs were anesthetized and subjected to endotoxin for 5 h. Eight of these pigs were given tezosentan (dual ET receptor antagonist) after 3 h. Cardiac effects were evaluated using the left ventricular (LV) pressure-volume relationship. Endotoxin was not associated with any effects on parameters of LV contractile function [end-systolic elastance (Ees), preload recruitable stroke work (PRSW), power(max)/end-diastolic volume (PWR(max)/EDV) and dP/dt(max)/end-diastolic volume (dP/dt(max)/EDV)] but with impairments in isovolumic relaxation (time constant for pressure decay, tau) and mechanical efficiency. Tezosentan administration decreased Ees, PWR(max)/EDV, and dP/dt(max)/EDV, while improving tau and LV stiffness. Thus, dual ET receptor antagonism was associated with a decline in contractile function but, in contrast, improved diastolic function. Positive hemodynamic effects from ET receptor antagonism in acute endotoxemia may be due to changes in cardiac load and enhanced diastolic function rather than improved contractile function.     

Ibuprofen attenuates cardiopulmonary dysfunction by modifying vascular tone in endotoxemia.

Ibuprofen, a cyclooxygenase inhibitor, improves pulmonary and cardiovascular injury in endotoxemia. We studied the mechanism of the beneficial effects of ibuprofen in relation to production of inflammatory mediators which influence vascular tone in endotoxemia. Rats were randomly assigned to one of three groups: (1) control, (2) endotoxemia alone; and (3) ibuprofen pretreatment and endotoxemia. Plasma and lung lavage concentrations of tumor necrosis factor, thromboxane B2 (TXB2), leukotriene (LT) C4,D4,E4 and nitric oxide (NO) were determined over a 2 h period. Pretreatment with ibuprofen resulted in increased survival, and attenuation of pulmonary and cardiovascular dysfunction when compared to the rats receiving endotoxin alone. The marked elevation in plasma TXB2 concentration in endotoxemic rats was prevented by pretreatment with ibuprofen. Similarly, pretreatment with ibuprofen prevented the decrease in lung lavage NO levels in endotoxemic rats. The improved survival and cardiopulmonary protection in endotoxemic rats pretreated with ibuprofen appears to be related to decreased thromboxane production and preservation of endothelial production of nitric oxide.     

Reversal of hyperdynamic response to continuous endotoxin administration by inhibition of NO synthesis.

Septic shock is characterized by an increase in cardiac output and a fall in systemic vascular resistance index and mean arterial pressure. Endotoxin alters the smooth muscle function of blood vessels, probably by means of an increased production of the potent vasodilator nitric oxide (NO). The present study was accomplished to determine how the inhibition of NO synthesis influences cardiovascular performance in an ovine model of hyperdynamic endotoxemia. Endotoxemia was induced in five range ewes (41 +/- 2 kg) by continuous infusion of Escherichia coli endotoxin (LPS, 10 ng.kg-1.min-1) over the entire study period. After 24 h of LPS infusion, cardiac output increased from 5.2 +/- 0.3 to 7.9 +/- 0.6 (SE) 1/min (P less than 0.05) and mean arterial pressure and systemic vascular resistance index fell from 92 +/- 5 to 79 +/- 6 mmHg (P = 0.08) and from 1,473 +/- 173 to 824 +/- 108 dyn.s.cm-5.m2 (P less than 0.05), respectively. The pulmonary shunt fraction increased from 0.23 +/- 0.03 to 0.32 +/- 0.03 (P less than 0.05). The intravenous administration of the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (25 mg/kg) 24 h after the start of the LPS infusion changed these values to approximately baseline levels over the subsequent 4 h. Although N omega-nitro-L-arginine methyl ester increased pulmonary arterial pressure and pulmonary vascular resistance (P less than 0.05), right and left ventricular stroke volume index showed no significant changes. It is concluded that NO has a major function in cardiovascular performance in endotoxemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of thyrotropin releasing hormone as a therapeutic intervention for endotoxemia

Thyrotropin releasing hormone (TRH) has been reported to reduce endotoxin-induced hypotension and mortality rate in conscious rats. Limited data are available to explain these effects. We evaluated hemodynamic parameters, metabolic function, tissue injury, and survival rate in three groups of instrumented conscious rats following intravenous endotoxin (20 mg/kg, LD/90-24 h) challenge. Pretreatment with TRH (2.0 mg/kg, i.v.) was administered 10 min before endotoxin (n = 10) and control (n = 10) animals were given an equivalent volume of saline. The post-treated group (n = 7) was given TRH at the nadir of the hypotensive response following endotoxin to duplicate published protocols. 5 min after endotoxin blood pressure and cardiac output were significantly higher in the post and pre-treatment groups, respectively, compared to the untreated group. There were no differences at other times. Systemic vascular resistance was not affected by either treatment mode at any time. TRH treatment following endotoxin resulted in transient increases in heart and respiration rates and decreased central venous pressure during the first 30 min. Metabolic function indicated by measurements of glucose, lactate, hematocrit, pH, PO2, and PCO2 at 60 and 240 min after endotoxin was not modified by TRH. The hemorrhagic small intestine characteristic of this model was not improved by either treatment mode. Mortality rates at 4 h after endotoxin were 20% for the untreated, 40% for the pre-treated, and 43% for the post-treated. These results suggest TRH exerts early transient effects on cardiovascular responses evoked by endotoxin in the conscious rat but no lasting beneficial effects were found to support the use of TRH as a mono-therapy for endotoxemia.     

Effect of synchronous increase in intrathoracic pressure on cardiac performance during acute endotoxemia

In the anesthetized closed-chest canine model of Gram-negative endotoxemia (n = 10), we tested the hypothesis that the effect of cardiac cycle-specific intrathoracic pressure pulses delivered by a heart rate-(HR) synchronized high-frequency jet ventilator (sync HFJV) on systolic ventricular performance is dependent on the level of preload. To control for HFJV frequency, hemodynamic responses were also measured at fixed frequency within 15% of HR (async HFJV). Biventricular stroke volumes (SV) were measured by electromagnetic flow probes. Measurements were made before (baseline) and 30 min after infusion of 1 mg/kg Escherichia coli endotoxin (serotype 055:B5) and then after 2 mg/kg propranolol at both low (less than 10 mmHg) left ventricular filling pressure (LVFP) and high (greater than 10 mmHg) LVFP. Ventricular function curves, aortic pressure-flow (P-Q) relationships, and venous return (VR) curves were analyzed. We found that endotoxin did not alter VR curves but shifted the aortic P-Q curves to the left with pressure on the x-axis (P less than 0.05). Volume loading increased SV (P less than 0.01) because of a rightward shift of the VR curve. No specific differences occurred with either sync or async HFJV during endotoxin, presumably because of preserved VR and shifted aortic P-Q. The lack of cardiac cycle-specific effects of ITP appears to be due to the selective endotoxin-induced changes in peripheral vasomotor tone that counterbalance any depressed myocardial contractility.     

Right ventricular TNF resistance during endotoxemia: the differential effects on ventricular function

Right and left ventricular myocytes originate from different cellular progenitors; however, it is unknown whether these cells differ in their response to endotoxemia. We hypothesized that 1) the percentage of endotoxemic functional depression within the right ventricle (RV) would be smaller than that of the left ventricle; and 2) that better RV function would correlate with lower levels of right ventricular TNF production. Adult Sprague-Dawley rats were divided into right and left control and endotoxin groups. Controls received vehicle, while endotoxin groups received LPS at 20 mg/kg ip. Hearts were excised either 2 or 6 h after injection. Hearts excised at 2 h were assayed for TNF, IL-6, TNF receptor 1 (TNFR1), TNFR2, and via ELISA, while hearts excised at 6 h were assayed via the Langendorff model. The percentage of cardiac functional depression, exhibited as developed pressure, contractility, and rate of relaxation (expressed as a percentage of control) was significantly smaller in right ventricles compared with left ventricles following endotoxin exposure. Tissue levels of TNF were significantly elevated in both right and left ventricles 2 h after endotoxin exposure, and right ventricular endotoxin groups expressed higher levels of TNF compared with their left ventricular counterparts. No significant differences in IL-6, TNFR1, or TNFR2 levels were noted between endotoxin-exposed ventricles. This is the first study to demonstrate that right and left ventricular function differs after endotoxin exposure.     

Efficacy of tumor necrosis factor α and eicosanoid inhibitors in experimental models of neonatal sepsis

Abstract The potential role of tumor necrosis factor α (TNFα) and eicosanoids in the pathogenesis of experimental neonatal sepsis models was investigated. Lethality was induced in neonatal rats by administration of heat killed group B streptococci (GBS, 7 mg kg⁻¹ intracardially) or Salmonella enteritidis endotoxin (0.35 mg kg⁻¹ intracardially). The relative efficacy of six compounds with putative TNFα and eicosanoid inhibitory actions were tested. These were: ibuprofen (3 and 20 mg kg⁻¹), a cyclo-oxygenase inhibitor; CGS85515 (30 mg kg⁻¹), a lipoxygenase inhibitor; LY203647 (30 mg kg⁻¹), a leukotriene D₄ receptor antagonist; pentoxifylline (10, 50 and 100 mg kg⁻¹), a TNF inhibitor; cloricromene (2 and 10 mg kg⁻¹), a thromboxane A₂ synthetase inhibitor with TNFα inhibitory actions; and SKF86002 (2.5, 5, 10 and 20 mg kg⁻¹), a dual cyclo-oxygenase/lipoxygenase inhibitor with TNFα inhibitory activity. Pentoxifylline, cloricromene and SKF86002, when given intraperitoneally 2 h before challenge, produced 45, 52 and 61% reductions, respectively, in plasma levels of TNFα at 2.5 h post-injection with killed GBS ( P < 0.05). On the contrary, pretreatment with ibuprofen, CGS85515 or LY203647 did not significantly affect TNFα levels. All compounds significantly attenuated the lethality by killed GBS and S. enteritidis endotoxin. These data suggest that TNFα and eicoisanoids contribute to the pathogenesis of shock induced by killed GBS and endotoxemia.     

Concentric adaptation of the left ventricle in response to controlled upper body exercise training.

Upper body exercise has many applications to the rehabilitation and maintenance of cardiovascular health of individuals who are unable to exercise their lower body. The hemodynamic loads of upper body aerobic exercise are characterized by relatively high blood pressure and relatively low venous return. It is not clear how the left ventricle adapts to the specific hemodynamic loads associated with this form of exercise training. The purpose of this study was to measure left ventricular structure and function in previously sedentary men by using echocardiography before and after 12 wk of aerobic arm-crank exercise training (n = 22) or a time control period (n = 22). Arm-crank peak oxygen consumption (in ml x kg(-1) x min(-1)) increased by 16% (P < 0.05) after training, and significant differences (P < 0.05) were found in wall thickness (from 0.86 to 0.99 cm) but not in left ventricular internal dimension in diastole or systole. This suggested a concentric pattern of left ventricular hypertrophy that persisted after scaling to changes in anthropometric characteristics. No differences (P < 0.05) were found for any measurements of resting left ventricular function. We conclude that upper body aerobic exercise training results in a specific left ventricular adaptation that is characterized by increased left ventricular wall thickness but no change in chamber dimension.     

Effects of flunixin meglumine on cardiopulmonary responses to endotoxin in ponies

The effects of endotoxemia on cardiopulmonary parameters, before and after cyclooxygenase blockade, were determined in anesthetized ponies spontaneously breathing a mixture of halothane and 100% O2. Escherichia coli endotoxin was infused intravenously at 20 micrograms/kg for 1 h followed by 10 micrograms X kg-1 X h-1 the subsequent 4 h. By 15 min endotoxin increased mean pulmonary arterial pressure (Ppa), pulmonary vascular resistance (PVR), and alveolar dead space ventilation (VDA/VT), and these were followed by a return to base-line values by 30 min. A second increase in PVR occurred by 5 h of endotoxemia. The early increases in Ppa, PVR, and VDA/VT were blocked by flunixin meglumine (FM), a cyclooxygenase inhibitor. Endotoxin decreased central plasma volume by 1 h and cardiac index by 3 h; hematocrit and plasma protein concentration were increased by 0.5 and 1.5 h, respectively, indicating a loss of plasma volume. These changes were also blocked or attenuated by FM. Moreover, in ponies treated with endotoxin + FM, cardiac index increased, indicating the presence of a cardiac-stimulating factor. We conclude that endotoxemia in ponies causes cardiopulmonary dysfunction that is mediated by cyclooxygenase-dependent and possibly cyclooxygenase-independent metabolites.     

The effect of systemic iNOS inhibition during human endotoxemia on the development of tolerance to different TLR-stimuli

The phenomenon of repeated exposure to endotoxin resulting in diminished release of pro-inflammatory cytokines is called endotoxin tolerance, in which there is a putative role for nitric oxide (NO). We investigated the effect of selective inducible NO-synthase (iNOS) inhibition during experimental human endotoxemia on the development of tolerance to various Toll-like receptor (TLR) agonists ex vivo. Volunteers received 2 ng/kg Escherichia coli endotoxin in the absence (n = 7) or presence (n = 7) of the selective iNOS inhibitor aminoguanidine (bolus 5 mM followed by a continuous infusion of 1.5 mmol/h). At 0, 2 and 4 h, blood samples were drawn for ex vivo stimulation with different TLR agonists. Experimental endotoxemia did not induce tolerance to TLR-2 and TLR-7 stimulation. In TLR-3, TLR-4 and TLR-5 stimulated whole blood, pro- and anti-inflammatory cytokine release was attenuated at 4 h, indicating that endotoxin-induced tolerance is not confined to subsequent TLR-4 stimulation alone. Aminoguanidine-treated subjects also developed tolerance to TLR-4 stimulation. In contrast, tolerance to TLR-3 stimulation did not occur for IL-10, and tolerance in TLR-5 stimulated blood did not develop for both pro- and anti-inflammatory cytokines. The role of NO in the development of tolerance is different for the various TLRs stimulated and pro- and anti-inflammatory cytokines measured.     

Verapamil attenuates lung vascular responses to endotoxin in sheep

Experiments were conducted on five chronically instrumented unanesthetized sheep to determine the effects of verapamil, a calcium channel inhibitor, on the pulmonary hemodynamic and microvascular permeability responses to endotoxemia. Paired control endotoxemia experiments (E) and endotoxemia with verapamil treatment (30-60 micrograms.kg-1.min-1) experiments (V + E) were conducted on each sheep in random order. In the V + E experiments sheep were pretreated with a continuous intravenous infusion of verapamil 1.5-2.0 h before endotoxin infusion (1.0 microgram/kg, given over 15 min). Verapamil significantly increased base-line pulmonary arterial pressure, left atrial pressure, lung lymph flow rate, and circulating blood leukocyte levels and significantly decreased base-line cardiac output. During the endotoxin response, verapamil significantly attenuated both phase I pulmonary arterial hypertension and phase II lung lymph flow rate compared with control endotoxin experiments. The results indicate that verapamil attenuates both the pulmonary hemodynamic and increased lung microvascular permeability response to endotoxin in sheep. In a series of in vitro experiments, verapamil was found to be a potent inhibitor of phorbol myristate acetate-induced superoxide production in isolated sheep granulocytes. These data suggest that the beneficial in vivo effects of verapamil during endotoxemia may in part be due to its inhibition of increased free cytosol calcium concentration and/or inhibition of toxic O2 metabolite production.     

Cardiac function and coronary flow in chronic endotoxemic pigs

We have reported that myocardial inotropism was depressed in acute and chronic endotoxemia. One possible mechanism for this observation is that endotoxemia reduces myocardial perfusion and indeed, we observed reduced myocardial perfusion in acute endotoxemia. This study tested the hypothesis that reduced inotropism of chronic endotoxemia was accompanied by reduced coronary artery blood flow. Fifteen pigs were equipped with left atrial and ventricular catheters, circumflex coronary and pulmonary artery flow meters, left ventricular pressure transducer, and ultrasonic crystals in the anterior-posterior axis to measure internal short axis diameter by sonomicrometry. The pigs recuperated for 3 days before basal data were collected over the next 3-5 days. After at least 7 postoperative days, an osmotic pump containing Salmonella enteriditis endotoxin was implanted in 12 pigs. Endotoxin was delivered at 10 micrograms/hr/kg for 2 days, at which time the animals were sacrificed. Osmotic pumps containing sterile saline were implanted in 3 pigs. Eight of the 12 endotoxemic pigs survived; 4 died before the morning of the second day. The survivors exhibited elevated heart rate, peak left ventricular systolic pressure, and cardiac output. Inotropism was evaluated by calculating the slope of the end-systolic pressure-diameter relationship (ESPDR) and % diameter-shortening. ESPDR was significantly depressed on the second endotoxemic day, while % diameter-shortening was depressed on both endotoxemic days. Coronary artery blood flow was significantly elevated on both endotoxemic days, while cross-sectional stroke work was unchanged. Therefore, the ratio of coronary blood flow to stroke work increased on both endotoxemic days. Nonsurvivors exhibited reduced heart rate, cardiac output, peak left ventricular systolic pressure, ESPDR, and % diameter-shortening. Neither coronary artery blood flow nor flow-to-work ratios increased in this group. Sham endotoxemic pigs demonstrated no cardiac or hemodynamic changes over 3 days. These results indicate that depressed inotropism during chronic endotoxemia was not caused by reduced coronary blood flow; rather, the myocardium was relatively overperfused.     

LPS-induced microvascular leukocytosis can be assessed by blue-field entoptic phenomenon

Administration of low doses of Escherichia coli endotoxin [a lipopolysaccharide (LPS)] to humans enables the study of inflammatory mechanisms. The purpose of the present study was to investigate whether the blue-field entoptic technique may be used to quantify the increase in circulating leukocytes in the ocular microvasculature after LPS infusion. In addition, combined laser Doppler velocimetry and retinal vessel size measurement were used to study red blood cell movement. Twelve healthy male volunteers received 20 IU/kg iv LPS as a bolus infusion. Outcome parameters were measured at baseline and 4 h after LPS administration. In the first protocol (n = 6 subjects), ocular hemodynamic effects were assessed with the blue-field entoptic technique, the retinal vessel analyzer, and laser Doppler velocimetry. In the second protocol (n = 6 subjects), white blood cell (WBC) counts from peripheral blood samples and blue-field entoptic technique measurements were performed. LPS caused peripheral blood leukocytosis and increased WBC density in ocular microvessels (by 49%; P = 0.036) but did not change WBC velocity. In addition, retinal venous diameter was increased (by 9%; P = 0.008), but red blood cell velocity remained unchanged. The LPS-induced changes in retinal WBC density and leukocyte counts were significantly correlated (r = 0.87). The present study indicates that the blue-field entoptic technique can be used to assess microvascular leukocyte recruitment in vivo. In addition, our data indicate retinal venous dilation in response to endotoxin.     

Effect of rowing ergometry and oral volume loading on cardiovascular structure and function during bed rest

This study examined the effectiveness of a short-duration but high-intensity exercise countermeasure in combination with a novel oral volume load in preventing bed rest deconditioning and orthostatic intolerance. Bed rest reduces work capacity and orthostatic tolerance due in part to cardiac atrophy and decreased stroke volume. Twenty seven healthy subjects completed 5 wk of -6 degree head down bed rest. Eighteen were randomized to daily rowing ergometry and biweekly strength training while nine remained sedentary. Measurements included cardiac mass, invasive pressure-volume relations, maximal upright exercise capacity, and orthostatic tolerance. Before post-bed rest orthostatic tolerance and exercise testing, nine exercise subjects were given 2 days of fludrocortisone and increased salt. Sedentary bed rest led to cardiac atrophy (125 ± 23 vs. 115 ± 20 g; P < 0.001); however, exercise preserved cardiac mass (128 ± 38 vs. 137 ± 34 g; P = 0.002). Exercise training preserved left ventricular chamber compliance, whereas sedentary bed rest increased stiffness (180 ± 170%, P = 0.032). Orthostatic tolerance was preserved only when exercise was combined with volume loading (-10 ± 22%, P = 0.169) but not with exercise (-14 ± 43%, P = 0.047) or sedentary bed rest (-24 ± 26%, P = 0.035) alone. Rowing and supplemental strength training prevent cardiovascular deconditioning during prolonged bed rest. When combined with an oral volume load, orthostatic tolerance is also preserved. This combined countermeasure may be an ideal strategy for prolonged spaceflight, or patients with orthostatic intolerance.     

Dexamethasone blocks increased leukotriene B4 production during endotoxin-induced lung injury

We hypothesized that leukotriene B4 (LTB4) might be produced during endotoxemia in pigs and, if so, might play a role in the pathophysiology of acute respiratory failure. Escherichia coli endotoxin (055-B5) was infused intravenously into anesthetized pigs at 5 micrograms/kg the 1st h, followed by 2 micrograms.kg-1.h-1 for 3 h. Endotoxemic pigs were treated with dexamethasone (DEX, iv) 18 h (5 mg/kg) and 1 h (5 mg/kg) before onset of endotoxemia. During phases I (i.e., 0-2 h) and II (i.e., 2-4 h), endotoxin decreased cardiac index, caused granulocytopenia, and increased mean pulmonary arterial pressure, pulmonary vascular resistance, alveolar-arterial O2 gradient, and hematocrit. During phase II, plasma LTB4 levels were increased (as determined by radioimmunoassay, reverse-phase high-performance liquid chromatography, and ultraviolet spectroscopy). Endotoxin increased the levels of LTB4 and albumin in bronchoalveolar lavage fluid (BALF). DEX blocked or greatly attenuated the endotoxin-induced hemodynamic abnormalities and blocked the increases in plasma and BALF LTB4 levels. We conclude that LTB4 is produced during porcine endotoxemia and could possibly play a role in the pathophysiology of endotoxin-induced lung injury in anesthetized pigs.     

Effects of cardiac preload reduction and dobutamine on hepatosplanchnic blood flow regulation in porcine endotoxemia

Insufficient cardiac preload and impaired contractility are frequent in early sepsis. We explored the effects of acute cardiac preload reduction and dobutamine on hepatic arterial (Qha) and portal venous (Qpv) blood flows during endotoxin infusion. We hypothesized that the hepatic arterial buffer response (HABR) is absent during preload reduction and reduced by dobutamine. In anesthetized pigs, endotoxin or vehicle (n = 12, each) was randomly infused for 18 h. HABR was tested sequentially by constricting superior mesenteric artery (SMA) or inferior vena cava (IVC). Afterward, dobutamine at 2.5, 5.0, and 10.0 μg/kg per minute or another vehicle (n = 6, each) was randomly administered in endotoxemic and control animals, and SMA was constricted during each dose. Systemic (cardiac output, thermodilution) and carotid, splanchnic, and renal blood flows (ultrasound Doppler) and blood pressures were measured before and during administration of each dobutamine dose. HABR was expressed as hepatic arterial pressure/flow ratio. Compared with controls, 18 h of endotoxin infusion was associated with decreased mean arterial blood pressure [49 ± 11 mmHg vs. 58 ± 8 mmHg (mean ± SD); P = 0.034], decreased renal blood flow, metabolic acidosis, and impaired HABR during SMA constriction [0.32 (0.18-1.32) mmHg/ml vs. 0.22 (0.08-0.60) mmHg/ml; P = 0.043]. IVC constriction resulted in decreased Qpv in both groups; whereas Qha remained unchanged in controls, it decreased after 18 h of endotoxemia (P = 0.031; constriction-time-group interaction). One control and four endotoxemic animals died during the subsequent 6 h. The maximal increase of cardiac output during dobutamine infusion was 47% (22-134%) in controls vs. 53% (37-85%) in endotoxemic animals. The maximal Qpv increase was significant only in controls [24% (12-47%) of baseline (P = 0.043) vs. 17% (-7-32%) in endotoxemia (P = 0.109)]. Dobutamine influenced neither Qha nor HABR. Our data suggest that acute cardiac preload reduction is associated with preferential hepatic arterial perfusion initially but not after established endotoxemia. Dobutamine had no effect on the HABR.     

Naloxone pretreatment prevents the bloody diarrhea of canine endotoxic shock

We examined the importance of timing with endorphin involvement in shock by giving the opiate receptor antagonist naloxone as a pretreatment in canine endotoxic shock. Dogs anesthetized with pentobarbital (30 mg/kg iv) were given Escherichia coli endotoxin at LD80 doses iv. Naloxone (2 mg/kg plus 2 mg/kg/hr iv, N = 10) started 15 min before endotoxin attenuated the fall in mean arterial pressure, cardiac index, and the first derivative of left ventricular pressure due to endotoxin in comparison with control animals given 0.9% NaCl (N = 10). Naloxone attenuated the endotoxin-induced decrease in superior mesenteric arterial blood flow and the increases in portal venous pressure and pulmonary arterial pressures. Moreover, naloxone pretreatment prevented the characteristic bloody diarrhea and reduced mortality. Our findings implicate endorphins acting on opiate receptors as important mediators of endotoxin-induced cardiovascular failure and bloody diarrhea in canine endotoxemia. These are early manifestations and dictate expeditious use of naloxone in endotoxic shock.     

Effect of a new synthetic free radical scavenger, 2-octadecyl ascorbic acid, on the mortality in mouse endotoxemia

Oxygen-derived free radicals have been implicated as mediators of cellular injury in several model systems. In order to clarify the role of oxygen radicals in endotoxemia, we measured the serial lipid peroxide changes resulting from systemic radical reactions using a newly developed colormetric method. To determine the effect of a free radical scavenger on mortality in endotoxemia, a new synthetic scavenger, 2-Octadecylascorbic acid (CV-3611), which overcome the detrimental properties (circulation half-life and cell penetration) of native SOD, was used in the model of mouse endotoxemia induced by the i.p. administration of E-coli endotoxin (10 mg/kg). Serial LPO (Lipid Peroxide) changes revealed significant elevations from the basal level of 4.52 +/- 0.79 nmol/ml to 10.5 +/- 2.04 nmol/ml at 2h (P less than 0.05), 12.0 +/- 2.44 nmol/ml at 8h (P less than 0.05), 32.8 +/- 12.5 nmol/ml at 12h (P less than 0.05) and 13.6 +/- 2.40 nmol/ml at 24h (P less than 0.05) following i.p. administration of E-coli. The circulation half life of CV-3611 was checked by a reversed-phase HPLC after 10 mg/kg s.c. administration. The level of CV-3611 reached peak levels of 0.54 +/- 0.10 micrograms/ml at 1h and 0.52 +/- 0.20 micrograms/ml at 2h then gradually decreased to the level of 0.04 +/- 0.004 micrograms/ml at 6h and to a non-detectable level at 24h after s.c. administration. Increased survival was seen at 2 days (P less than 0.001) after E-coli endotoxin administration in the CV-3611 treated group compared to the control group. These results suggest that oxygen derived free radicals contribute to mortality in mouse endotoxemia and that antioxidants such as CV-3611 may provide a new therapeutic avenue by improving survival of patients with gram-negative bacterial sepsis.     

Endotoxin-induced liver hypoxia: defective oxygen delivery versus oxygen consumption.

In vivo EPR was used to investigate liver oxygenation in a hemodynamic model of septic shock in mice. Oxygen-sensitive material was introduced either (i) as a slurry of fine particles which localized at the liver sinusoids (pO2 = 44.39 +/- 5.13 mmHg) or (ii) as larger particles implanted directly into liver tissue to measure average pO2 across the lobule (pO2 = 4.56 +/- 1.28 mmHg). Endotoxin caused decreases in pO2 at both sites early (5-15 min) and at late time points (6 h after endotoxin; sinusoid = 11.22 +/- 2.48 mmHg; lobule = 1.16 +/- 0.42 mmHg). The overall pO2 changes observed were similar (74.56% versus 74.72%, respectively). Blood pressures decreased transiently between 5 and 15 min (12.88 +/- 8% decrease) and severely at 6 h (59 +/- 9% decrease) following endotoxin, despite volume replacement with saline. Liver and circulatory nitric oxide was elevated at these times. Liver oxygen extraction decreased from 44% in controls to only 15% following endotoxin, despite severe liver hypoxia. Arterial oxygen saturation, blood flow (hepatic artery), and cardiac output were unaffected. Pretreatment with l-NMMA failed to improve endotoxin-induced oxygen defects at either site, whereas interleukin-13 preserved oxygenation. These site-specific measurements of pO2 provide in vivo evidence that the principal cause of liver hypoxia during hypodynamic sepsis is reduced oxygen supply to the sinusoid and can be alleviated by maintaining sinusoidal perfusion.     

Protection of lung tissue against ischemia/reperfusion injury by preconditioning with inhaled nitric oxide in an in situ pig model of normothermic pulmonary ischemia

Topical administration of nitric oxide (NO) by inhalation is currently used as therapy in various pulmonary diseases, but preconditioning with NO to ameliorate lung ischemia/reperfusion (I/R) injury has not been fully evaluated. In this study, we investigated the effects of NO inhalation on functional pulmonary parameters using an in situ porcine model of normothermic pulmonary ischemia. After left lateral thoracotomy, left lung ischemia was maintained for 90 min, followed by a 5h reperfusion period (group I, n = 7). In group II (n = 6), I/R was preceded by inhalation of NO (10 min, 15 ppm). Animals in group III (n = 7) underwent sham surgery without NO inhalation or ischemia. In order to evaluate the effects of NO preconditioning, lung functional and hemodynamic parameters were measured, and the zymosan-stimulated release of reactive oxygen species in arterial blood was determined. Animals in group I developed significant pulmonary I/R injury, including pulmonary hypertension, a decreased pO(2) level in pulmonary venous blood of the ischemic lung, and a significant increase of the stimulated release of reactive oxygen species. All these effects were prevented, or the onset (release of reactive oxygen species) was delayed, by NO inhalation. These results indicate that preconditioning by NO inhalation before lung ischemia is protective against I/R injury in the porcine lung.