Hemorrhagic shock primes the hepatic portal circulation for the vasoconstrictive effects of endothelin-1

The effects of hemorrhagic shock secondary to hepatectomy in a swine model

BACKGROUND

Ischemia-reperfusion injury caused by severe hemorrhagic shock and subsequent resuscitation leads to deterioration of hepatic homeostasis and possibly to liver failure. The present study focuses on determining whether there is a different biological response to hemorrhagic shock by different sources of hemorrhage, hepatic hemorrhage (HH) versus peripheral hemorrhage.

METHODS

Twenty-one male swine (Sus scrofa domesticus) were randomly allocated in three groups as follows: sham group (S, n = 5), central venous hemorrhage group, (CVH) (n = 8), and HH group (n = 8). Hepatectomy of the left liver lobe was carried out in groups CVH and HH, and the animals were subjected to controlled bleeding from the internal jugular vein and the traumatic liver surface, respectively. After 10 min of hemorrhage, shock was maintained for 30 min at mean arterial pressure levels of 30 mm Hg-40 mm Hg and resuscitation was initiated with crystalloids and colloids. Hemodynamic parameters and fluid balance were monitored throughout the 6 h of total duration of the experiment. Blood samples were collected at 0-, 40-, and 360-min time points for transaminases, albumin, and interleukin-6 measurement. Hepatic tissue was harvested at the end of the experiment for oxidative marker and proliferation analysis.

RESULTS

Although blood loss was comparable between the two groups, the amount of fluids needed for resuscitation was higher for the HH group. Inflammatory response, measured by interleukin-6, was found higher in HH group. Oxidative stress markers did not reveal statistically significant difference between the two groups. Liver hemorrhage decreased hepatocellular proliferation measured by proliferating cell nuclear antigen.

CONCLUSIONS

Our study provides evidence that HH entails worse consequences for the hepatocytes than systemic hemorrhage. Higher needs for resuscitation fluids, decreased proliferation, and augmented inflammatory response when HH takes place are findings with possible clinical importance in liver surgery and trauma.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Tezosentan normalizes hepatomesenteric perfusion in a porcine model of cardiac tamponade

BACKGROUND

To investigate endothelin-1 (ET-1)-dependent hepatic and mesenteric vasoconstriction, and oxygen and lactate fluxes in an acute, fixed low cardiac output (CO) state.

METHODS

Sixteen anesthetized, mechanically ventilated pigs were studied. Cardiac tamponade was established to reduce portal venous blood flow (Q(PV)) to 2/3 of the baseline value. CO, hepatic artery blood flow (Q(HA)), Q(PV), hepatic laser-Doppler flow (LDF), hepatic venous and portal pressure, and hepatic and mesenteric oxygen and lactate fluxes were measured. Hepatic arterial (R(HA)), portal (R(HP)) and mesenteric (R(mes)) vascular resistances were calculated. The combined ET(A)-ET(B) receptor antagonist tezosentan (RO 61-0612) or normal saline vehicle was infused in the low CO state. Measurements were made at baseline, after 30, 60, 90 min of tamponade, and 30, 60, 90 min following the infusion of tesozentan at 1 mg/kg/h.

RESULTS

Tamponade decreased CO, Q(PV), Q(HA), LDF, hepatic and mesenteric oxygen delivery, while hepatic and mesenteric oxygen extraction and lactate release increased. R(HA), R(HP) and R(mes) all increased. Ninety minutes after tesozentan, Q(PV), LDF and hepatic and mesenteric oxygen delivery and extraction increased approaching baseline values, but no effect was seen on CO or Q(HA). Hepatic and mesenteric handling of lactate converted to extraction. R(HA), R(HP) and R(mes) returned to baseline values. No changes were observed in these variables among control animals not receiving tesozentan.

CONCLUSION

In a porcine model of acute splanchnic hypoperfusion, unselective ET-1 blockade restored hepatomesenteric perfusion and reversed lactate metabolism. These observations might be relevant when considering liver protection in low CO states.

UP-REGULATED THROMBOXANE PRODUCTION IN THE RAT LIVER WITH BILIARY OBSTRUCTION DOES NOT CONTRIBUTE TO PROMOTE HEPATIC INJURY

This study sought to determine whether in vivo inhibition of thromboxane A2 (TXA2) action contribute to attenuate hepatic damage after bile duct ligation (BDL). Male Wistar rats were assigned to sham operation or BDL. At the time of operation, infusion pump with saline, ozagrel natrium (TXA2 synthase inhibitor), or SQ29548 (TXA2 receptor antagonists) was implanted in the abdominal cavity. Plasma alanine aminotransferase, aspartate aminotransferase, hyaluronic acid, and total bilirubin levels were measured at 4 days after the operation. The levels of plasma TXB2, a stable metabolite of TXA2, were significantly increased after BDL. Gene expression of TXA2 synthase was also significantly upregulated in the liver. Nonetheless, either an inhibition of TXA2 synthesis by ozagrel natrium or a blockade of TXA2 receptor by SQ29548 has no effect in every measured parameter related to hepatic function. These results indicated that despite a highly increased production in the liver, TXA2 is not directly related to the hepatic injury in BDL rats.

Current Understanding of Gender Dimorphism in Hepatic Pathophysiology1

Studies have shown gender dimorphic response of the liver for various hepatic stresses including ischemia/reperfusion, hemorrhagic shock-resuscitation, hepatectomy, liver cirrhosis, endotoxemia, and chronic alcoholic consumption. The mechanisms responsible for the gender dimorphic response include differences in pro-inflammatory cytokine release, production of reactive oxygen species, and alteration in hepatic vasoregulatory action. These effects were shown to be modulated by circulating sex steroid levels. In this regard, modulation of sex steroid levels by agents/drugs has been proposed as a therapeutic option for preventing hepatic damage in various hepatic stress models. Further elucidation of precise mechanisms responsible for the gender-related differences in the hepatic pathophysiology is essential for the potential clinical application of sex hormone modulation therapy. In this article, current progress in our understanding the gender difference in the hepatic pathophysiology under the condition of hepatic stress is reviewed and discussed.

Estradiol's effect on portal response to endothelin-1 after trauma-hemorrhage

BACKGROUND

The fine balance between vasoconstrictors and vasodilators maintains portal circulation. Studies have shown that portal response to endothelin-1 (ET-1), a potent vasoconstrictor, is enhanced following hemorrhagic-shock, which subsequently leads to the impaired hepatic circulation and hepatic damage. Although protective effects of 17beta-estradiol (E(2)) against hepatic damage following trauma-hemorrhage have been observed, it remains unknown whether E(2) directly improves hepatic circulation. We hypothesized that the salutary effects of E(2) are mediated, at least in part, by the attenuation of portal response to ET-1 following trauma-hemorrhage.

MATERIALS AND METHODS

Male adult Sprague-Dawley rats were randomly assigned to sham operation or trauma-hemorrhage with or without in vivo E(2) treatment. Trauma-hemorrhage included midline laparotomy and approximately 90 min of hemorrhagic shock (35 mmHg), then resuscitation with four times the shed blood volume with Ringer's lactate solution over 60 min. For the E(2) treatment group, 1 mg/kg of E(2) was added to the Ringer's lactate solution. At 5 h after the end of resuscitation, the liver was isolated and perfused in vitro to measure portal pressure responses to exogenous ET-1 (60 pmol in 150 ml perfusate, bolus) with or without E(2) (1,500 pg/ml).

RESULTS

Peak portal pressure after the administration of ET-1 was significantly higher in vehicle-treated trauma-hemorrhage group compared with the sham group. This effect was significantly attenuated in the E(2) treatment group. Furthermore, E(2) treatment restored bile production and prevented hepatic damage following trauma-hemorrhage.

CONCLUSIONS

The beneficial effects of estradiol observed following trauma-hemorrhage, at least partly, are caused by the attenuation of portal pressure response to increased ET-1.

Perflubron emulsion improves hepatic microvascular integrity and mitochondrial redox state after hemorrhagic shock

Hemorrhagic shock is associated with decreased systemic oxygen delivery, but also with impaired microvascular perfusion, which can result in diminished local oxygen availability even in the presence of adequate cardiac output after resuscitation. Beside surgical interventions to control blood loss, transfusion of stored packed red blood cells represents the current standard of care in the management of severe hemorrhagic shock. Because stored red blood cells are less deformable and show a higher O2 affinity that affects the O2 off-load to tissues, perfluorocarbon-based artificial oxygen carriers might improve local O2 delivery under these conditions. To test this, rats were subjected to hemorrhagic shock (1 h, mean arterial pressure [MAP] 30-35 mmHg) and were resuscitated with fresh whole blood, pentastarch, stored red blood cells, perflubron emulsion (2.7 and 5.4 g/kg body weight) together with pentastarch, or stored red blood cells together with 2.7 g/kg perflubron emulsion. Hepatic microcirculation, tissue oxygenation, and mitochondrial redox state were investigated by intravital microscopy. In addition, hepatocellular function and liver enzyme release were determined. After hemorrhagic shock and resuscitation with perflubron emulsion, volumetric sinusoidal blood flow was significantly increased compared with resuscitation with stored red blood cells. Furthermore, resuscitation with perflubron emulsion resulted in higher hepatic tissue PO2 and normalized mitochondrial redox potential, which was accompanied by lessened hepatocellular injury as well as improved liver function. These results indicate that, in this model of hemorrhagic shock, asanguineous fluid resuscitation with addition of perflubron emulsion is superior to stored blood or pentastarch alone with respect to increased local O2 availability on the cellular level. This effect is primarily due to improved restoration of hepatic microcirculatory integrity.

Role of thromboxane in producing portal hypertension following trauma-hemorrhage

Thromboxane A2 (TXA2) and endothelin-1 (ET-1) have been proposed as the important vasoconstrictors that increase portal venous resistance in paracrine or autocrine fashion. We hypothesized that the hepatic damage following trauma-hemorrhage (T-H) is induced by the impaired hepatic circulation due to the increased production of vasoconstrictors such as ET-1 and TXA2 by the liver. To test this, male Sprague-Dawley rats (n = 6/group) were subjected to trauma (i.e., midline laparotomy) and hemorrhage (35-40 mmHg for 90 min followed by fluid resuscitation) or sham operation. At 2 or 5 h after the end of resuscitation, the liver was isolated and perfused and portal inflow pressure, bile flow, and release of ET-1 and thromboxane B2 (TXB2; a stable metabolite of TXA2) into the perfusate were measured. The level of portal pressure was higher at 5 h following T-H compared with 2 h after T-H and sham. The portal pressure was inversely correlated to the amount of bile production. Furthermore, the bile flow was significantly correlated to the hepatic damage as evidenced by release of lactate dehydrogenase into the perfusate. The level of ET-1 at 5 h following T-H in the perfusate after 30 min of recirculation did not show any difference from sham. However, the levels of TXB2 in the T-H group were significantly higher than those in sham at that interval. These results indicate that the increased release of TXA2 but not ET-1 following T-H might be responsible for producing the increased portal resistance, decreased bile production, and hepatic damage.

Intravascular infusion of acid promotes intrapulmonary inducible nitric oxide synthase activity and impairs blood oxygenation in rats

OBJECTIVE

To test the hypothesis that intravascular acid infusion promotes intrapulmonary nitric oxide formation by promoting inducible nitric oxide synthase (iNOS) and inhibiting endothelial nitric oxide synthase (eNOS) expression in rats.

DESIGN

Prospective, placebo controlled, randomized laboratory study.

SETTING

University laboratory.

SUBJECTS

Twelve male Sprague-Dawley rats weighing 317 +/- 30 g served as study subjects. All animals were anesthetized, paralyzed, and mechanically ventilated throughout the experiment.

INTERVENTIONS

The animals were randomized to receive either 0.1 N hydrochloric acid or 0.9% saline intravenously. The infusions were initially given at a rate of 11 mL/kg/hr for 15 mins and then at a rate of 0.95 mL/kg/hr for the remainder of the experiment. Exhaled nitric oxide concentrations and hemodynamic measurements were monitored throughout the experiment. Lung tissues were harvested for Western blot analysis and immunostaining 4 hrs after starting the intravascular infusion.

MEASUREMENT AND MAIN RESULTS

At the end of the experiment, we found more than a four-fold higher concentration of exhaled nitric oxide in the acid-treated animals than in the saline-treated animals (p <.001). Western blot analysis revealed that the acid infusion increased intrapulmonary iNOS concentrations (p <.001), yet it decreased intrapulmonary eNOS concentrations (p =.009). Acid-related lung injury manifested as a decrease in blood oxygen tensions (p =.045) and as an increase in lung homogenate interleukin-6 concentrations (p =.003).

CONCLUSIONS

Our results reveal that hydrochloric acid infusion stimulates intrapulmonary nitric oxide formation at least in part by promoting the expression of iNOS. Our findings suggest that correcting acidosis should attenuate iNOS formation. Our data also support the idea that metabolic acidosis itself can lead to impaired intrapulmonary gas exchange and increased expression of pro-inflammatory cytokines such as interleukin-6. Whether the induction of intrapulmonary nitric oxide formation mediates or simply indicates lung injury warrants further investigation.

Effects of the intermittent Pringle manoeuvre on hepatic gene expression and ultrastructure in a randomized clinical study

BACKGROUND

The intermittent Pringle manoeuvre during hepatectomy results in a better clinical outcome when the accumulated ischaemia time is less than 120 min. The aim of this study was to investigate hepatic gene expression related to microcirculatory modulation and ultrastructural changes in patients having the intermittent Pringle manoeuvre.

METHODS

Forty patients who underwent hepatectomy for liver tumours were randomly assigned to liver transection with intermittent Pringle manoeuvre (Pringle group, n = 20) or without the manoeuvre (control group, n = 20). The clinical data and hepatic expression of endothelin (ET) 1 and endothelial nitric oxide synthase (eNOS) combined with liver ultrastructure were compared.

RESULTS

The Pringle manoeuvre resulted in less blood loss (8.9 versus 12.4 ml/cm(2); P = 0.034), a shorter transection time (2.7 versus 4.1 min/cm(2); P = 0.015) and a lower serum bilirubin level on postoperative day 2 (26 versus 35 microm/l; P = 0.04). The hepatic messenger RNA content of ET-1 decreased by 38 per cent of the basal level in the Pringle group, whereas it increased by 28 per cent in the control group (P = 0.026). More patients in the control group showed swelling of mitochondria in hepatocytes and disruption of sinusoidal lining cells (12 of 20 patients versus three of 20 in the Pringle group; P = 0.008).

CONCLUSION

The intermittent Pringle manoeuvre results in less disturbance of the hepatic microcirculation and better preservation of liver sinusoids after hepatectomy.