Plasma endothelin level changes during hemorrhagic shock

Alterations in endothelin receptors following hemorrhage and resuscitation by centhaquin

Endothelin-1 (ET-1) acts on ET(A) and ET(B) receptors and has been implicated in hemorrhagic shock (shock). We determined effect of shock and resuscitation by hypertonic saline (saline) or centhaquin on ET(A) and ET(B) receptor expression. Rats were anesthetized, a pressure catheter was placed in the left femoral artery; blood was withdrawn from the right femoral artery to bring mean arterial pressure (MAP) to 35 mm Hg for 30 min, resuscitation was performed and 90 min later sacrificed to collect samples for biochemical estimations. Resuscitation with centhaquin decreased blood lactate and increased MAP. Protein levels of ET(A) or ET(B) receptor were unaltered in the brain, heart, lung and liver following shock or resuscitation. In the abdominal aorta, shock produced an increase (140 %) in ET(A) expression which was attenuated by saline and centhaquin; ET(B) expression was unaltered following shock but was increased (79 %) by centhaquin. In renal medulla, ET(A) expression was unaltered following shock, but was decreased (-61 %) by centhaquin; shock produced a decrease (-34 %) in ET(B) expression which was completely attenuated by centhaquin and not saline. Shock induced changes in ET(A) and ET(B) receptors in the aorta and renal medulla are reversed by centhaquin and may be contributing to its efficacy.

Endothelin-1 attenuates increases in hydraulic conductivity due to platelet-activating factor via prostacyclin release

We previously showed that endothelin-1 (ET-1) and prostacyclin (PGI(2)) similarly attenuate increases in microvascular permeability induced by platelet-activating factor (PAF). This led us to hypothesize that ET-1 attenuates trans-endothelial fluid flux during PAF through PGI(2) release. We tested this hypothesis in three phases. First, bovine pulmonary artery endothelial cells were exposed to 0.008-8 μM ET-1 and assayed for PGI(2) release. Second, to determine whether increased transmonolayer flux after PAF could be attenuated by ET-1 or PGI(2) and reversed by PGI(2) synthesis inhibition or PGI(2) receptor blockade, we measured endothelial cell transmonolayer flux after cells were exposed to 10 nM PAF plus 10 μM PGI(2) or 80 pM ET-1, with or without 500 μM tranylcypromine (PGI(2) synthase inhibitor) or 20 μM CAY-10441 (PGI(2) receptor blocker). Finally, hydraulic conductivity (L(p)) was measured in rat mesenteric venules in vivo after exposure to 10 nM PAF and 80 pM ET-1 with or without tranylcypromine (100 and 500 μM) or CAY-10441 (2 and 20 μM). We found that in vitro, ET-1 stimulated a dose-dependent increase in PGI(2) production (from 126 to 217 pg/ml, P < 0.01). Compared with PAF alone, PGI(2) plus PAF and ET-1 plus PAF decreased transmonolayer flux similarly by 52 and 46%, respectively (P < 0.01), while tranylcypromine and CAY-10441 reversed these effects by 92 and 47%, respectively (P < 0.05). In vivo, PAF increased L(p) fourfold (P < 0.01) and ET-1 attenuated this effect by 83% (P < 0.01). Tranylcypromine and CAY-10441 reversed the ET-1 attenuation in L(p) during PAF by 55 and 45%, respectively (P < 0.01). We conclude that ET-1 may stimulate endothelial cell PGI(2) release to attenuate the increases in transmonolayer flux and hydraulic conductivity secondary to PAF.

Which Gender is Better Positioned in the Process of Liver Surgery? Male or Female?

Liver surgery is a process which induces various types of stress on the liver including the total occlusion of the blood inflow, hemorrhage, massive volume reduction, and postoperative infection. Animal studies have shown a gender dimorphic response of the liver for various stresses such as ischemia/reperfusion, hemorrhage/resuscitation, hepatectomy, portal branch ligation, and endotoxemia. Most of these studies demonstrated the female liver to be more tolerant under stressful conditions than the male liver. Estrogen, which is a representative female sex hormone, may be one of the responsible factors for this gender dimorphism. The mechanism of estrogen's salutary effect includes circulatory improvement, a reduced inflammatory response, a reduced oxygen radical production, and an improved hepatic regeneration. However, the clinical evidence that supports the results of these experimental studies is still insufficient. A well-controlled prospective clinical study is necessary to clarify the role of gender or sex hormone in the process of liver surgery. This may not only lead to a deeper understanding of the liver pathophysiology, but also to the possibility of hepatoprotective therapy using sex hormone modulators. This review summarizes the current understanding of gender dimorphism in the tolerance of the liver to various hepatic stresses, which occur during the process of major liver surgery.

Adrenomedullin and adrenomedullin binding protein-1 prevent metabolic acidosis after uncontrolled hemorrhage in rats

OBJECTIVE

Management of trauma victims with uncontrolled hemorrhage remains a major problem in combat casualty care at the far-forward battlefield setting. The neuroendocrine response to hemorrhage is to maintain perfusion to the heart and brain, often at the expense of other organ systems. Decreased organ perfusion after hemorrhagic shock is associated with metabolic acidosis, in which the up-regulated endothelin-1 plays an important role. We have recently shown that vascular responsiveness to adrenomedullin (AM), a newly discovered vasodilator peptide, is depressed after hemorrhage and resuscitation. Down-regulation of AM binding protein (AMBP-1) appears to be responsible for this hyporesponsiveness. We therefore hypothesized that administration of AM/AMBP-1 would prevent metabolic acidosis after uncontrolled hemorrhage via down-regulation of endothelin-1.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

A research institute laboratory.

SUBJECTS

Male Sprague-Dawley rats (275-325 g).

INTERVENTIONS

A rat model of uncontrolled hemorrhage with an extremely low volume of fluid resuscitation was used to mimic the combat situation.

MEASUREMENTS AND MAIN RESULTS

Both lumbar veins of male adult rats were isolated and severed at the junction to the vena cava. The abdomen was kept open but covered with a saline wet gauze for 45 mins and then closed in layers. The animals received 1 mL of normal saline (vehicle) with or without AM (12 microg/kg of body weight) and AMBP-1 (40 microg/kg of body weight) over 45 mins. Various variables were measured at 4 hrs after resuscitation. The bleed-out volumes in the vehicle group and the AM/ AMBP-1 treatment group were 6.78 +/- 0.19 and 6.81 +/- 0.25 mL/rat, respectively. The results indicate that AM/AMBP-1 administration prevented metabolic acidosis, mitigated organ injury, down-regulated preproendothelin-1 gene expression, and decreased plasma levels of endothelin-1 after hemorrhage.

CONCLUSIONS

AM/AMBP-1 may provide a novel approach for the treatment of uncontrolled hemorrhage. The beneficial effect of AM/AMBP-1 is associated with down-regulation of endothelin-1.

Role of endothelin-1 and cyclic nucleotides in ischemia/reperfusion-mediated microvascular leak

BACKGROUND

A consequence of ischemia/reperfusion (IR) is endothelial barrier dysfunction and intravascular volume loss. The purposes of our study are to explore the impact of: 1) cyclic guanosine monophosphate (cGMP) synthesis inhibition, 2) cyclic adenosine monophosphate (cAMP) synthesis inhibition, 3) treatment with endothelin-1, and 4) endothelin-1 (ET-1)-mediated cAMP changes on IR-induced fluid leak. We hypothesize that IR-mediated microvascular fluid leak results from increased cGMP activity and ET-1 decreases IR-induced fluid leak via cAMP.

METHODS

A micro-cannulation technique was used to determine fluid leak or hydraulic permeability (Lp) in rat mesenteric venules. Lp was measured during IR and after treatment with 1) cGMP synthesis inhibitor (LY83583,10 micromol/L) 2) cAMP synthesis inhibitor (2',5'dideoxyadenosine,10 micromol/L), 3) ET-1 (80 pM), and 4) cAMP synthesis inhibitor plus ET-1 (n=6 in each group; Lp represented as mean+/-standard error of the mean; units 10-cm/sec/cmH2O).

RESULTS

IR resulted in an increase in Lp (Lp=7.07+/-0.20) sevenfold above baseline (1.05+/-0.31) (p<or=0.001). Compared with IR alone, 1) pretreatment with cGMP synthesis inhibitor completely blocked IR-induced fluid leak (Lp=1.08+/-0.18) (p<or=0.001), 2) pretreatment with cAMP synthesis inhibitor attenuated fluid leak (Lp=3.92+/-0.20) (p<or=0.005), 3) treatment with ET-1 decreased fluid leak (Lp=5.38+/-0.28) (p<or=0.005), and 4) pretreatment with a cAMP inhibitor plus treatment with ET-1 reduced fluid leak nearly 50% compared with ET-1 alone (Lp=2.95+/-0.12) (p<or=0.005).

CONCLUSION

cGMP inhibition completely blocks fluid leak, pointing toward a central role as a mediator of IR-induced postcapillary venular leak. ET-1 mildly decreased leak. Furthermore, ET-1 may not exert its effects on microvascular fluid leak during IR via cAMP.

Angiotensin II effect on hydraulic permeability: interaction with endothelin-1, nitric oxide, and platelet activating factor

BACKGROUND

The purposes of this study were: 1) to examine the influence of endothelin (ET-1) release on the ability of angiotensin (Ang) II to modulate permeability, 2) to determine if the action of Ang II on microvascular permeability is dependent on nitric oxide (NO) release, and 3) to explore the effect of Ang II in microvessels activated with platelet activating factor (PAF).

METHODS

Hydraulic permeability (L(p)) was measured using the modified Landis in vivo micro occlusion technique during perfusion with: 1) the ET-1 receptor antagonist PD145065 (50 microM), then PD145065 + Ang II, 2) Ang II (20 nm), a NO synthase inhibitor L-NAME (100 microM), then L-NAME + Ang II, and 3) after endothelial activation with 10 nM of PAF, then PAF + Ang II.

RESULTS

1) The ET-1 antagonist increased L(p) 2.5-fold, Ang II alone increased L(p) five-fold, while Ang II perfusion during ET-1 antagonism increased L(p) over 6-fold (P < 0.04); 2) L-NAME increased L(p) over 3-fold. Ang II perfusion during NO synthase inhibition had no effect compared to NO synthase inhibition alone (P = 0.9) while Ang II alone increased L(p) 5-fold (P < or = 0.01); 3) PAF + Ang II (L(p) = 2.74 +/- 0.12) was decreased versus PAF alone (L(p) = 4.66 +/- 0.25) (P < 0.02).

CONCLUSIONS

Ang II does not increase hydraulic permeability via ET-1 release. Ang II may act via NO release to increase hydraulic permeability in the basal state. Finally, Ang II attenuates the increase in hydraulic permeability because of endothelial activation with platelet activating factor.

Cyclic nucleotide second messengers (cAMP and cGMP) play a central role in signal transduction and regulation of mesenteric postcapillary fluid leak

BACKGROUND

Endothelial cell receptors involved in post-injury/sepsis fluid extravasation are coupled to G-proteins that stimulate production of cGMP and cAMP. We hypothesize that cGMP and cAMP are endothelial second messengers that control microvascular permeability. The purposes of this series of experiments are to determine microvascular permeability under the following conditions: 1) reduced cGMP levels, 2) elevated cGMP levels, 3) reduced cAMP levels, and 4) elevated cAMP levels.

METHODS

Rat mesenteric venules were cannulated and hydraulic permeability (Lp) was measured at 3 to 5 minute intervals during 1) cGMP synthesis inhibition, 2) inhibition of cGMP degradation, 3) cAMP synthesis inhibition, and 4) inhibition of cAMP degradation (n = 6 in each study group). Lp units are x10 cm(-7)/sec/cmH2O and represented as mean +/- SEM.

RESULTS

Compared with baseline Lp (1.10 +/- 0.06), reduced cGMP levels by inhibiting its synthesis decreased Lp by over 50% (0.50 +/- 0.02, p < 0.001), while elevated cGMP levels by preventing its degradation increased Lp by more than 2-fold (0.91 +/- 0.10 to 2.26 +/- 0.15, p < 0.001). The reduction of cAMP levels by synthesis inhibition elevated Lp over 400% from 0.92 +/- 0.04 to 4.11 +/- 0.54 (p < 0.001), and elevation of cAMP level by blocking its degradation reduced Lp almost 50% from 1.11 +/- 0.04 to 0.59 +/- 0.06 (p < 0.001).

CONCLUSIONS

The second messengers, cGMP and cAMP, contribute to the control mechanisms that govern fluid leak across the endothelial barrier: cGMP increases microvascular permeability, while cAMP decreases microvascular permeability. Endothelial cell cyclic nucleotide second messengers are pharmacologically accessible and may be targeted during post-injury/sepsis-associated microvascular fluid leak.

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.

Gender differences in small intestinal perfusion following trauma hemorrhage: the role of endothelin-1

Although gender differences in intestinal perfusion exist following trauma-hemorrhage (T-H), it remains unknown whether endothelin-1 (ET-1) plays any role in these dimorphic responses. To study this, male, proestrus female (female), and 17 beta-estradiol (E2)-treated male rats underwent midline laparotomy, hemorrhagic shock (blood pressure 40 mmHg, 90 min), and resuscitation (Ringer lactate, 4X shed blood volume, 1 h). Two hours thereafter, intestinal perfusion flow (IPF) was measured using isolated intestinal perfusion. The IPF in sham-operated males was significantly lower than those in other groups and decreased markedly following T-H. In contrast, no significant decrease in IPF was observed in females and E2 males following T-H. The lower IPF in sham-operated males was significantly elevated by ET(A) receptor antagonist (BQ-123) administration and was similar to that seen in sham-operated females. The decreased IPF in males after T-H was also attenuated by BQ-123 administration. The intestinal ET-1 levels in sham-operated males were significantly higher than in other groups. Although plasma and intestinal ET-1 levels increased significantly after T-H in all groups, they were highest in males. Plasma E2 levels in females and E2 males were significantly higher than in males; however, they were not affected by T-H. There was a negative correlation between plasma ET-1 and E2 following T-H. Thus ET-1 appears to play an important role in intestinal perfusion failure following T-H in males. Because E2 can modulate this vasoconstrictor effect of ET-1, these findings may partially explain the previously observed salutary effect of estrogen in improving intestinal perfusion following T-H in males.

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.

Endothelin-1 decreases microvessel permeability after endothelial activation

BACKGROUND

Endothelin-1 (ET-1) is a potent vasoconstrictor that is released during shock and sepsis. We hypothesized that ET-1 plays a role in the modulation of the elevated microvascular permeability state of the activated endothelium.

METHODS

Hydraulic permeability (Lp) was measured using the modified Landis micro-occlusion technique. The effect of different ET-1 doses on Lp was determined by obtaining paired measures of Lp at baseline and after the vessels were perfused with ET-1 at doses of 2.0 pg/mL (n = 6), 20 pg/mL (n = 6), 200 pg/mL (n = 6), or 2,000 pg/mL (n = 6). To evaluate the effects of ET-1 in the activated endothelium, additional vessels were perfused with either 10 micromol/L adenosine triphosphate (ATP) (n = 6) or 1 nmol/L bradykinin (n = 6). The vessels were then perfused with 200 pg/mL ET-1 followed by the final L determination.

RESULTS

ET-1 significantly decreased Lp at doses of 20 pg/mL (p = 0.03), 200 pg/mL (p = 0.03), and 2,000 pg/mL (p = 0.01). Endothelial activation with ATP and bradykinin increased Lp to 4.21 +/- 0.39 (p < 0.0001) and 2.72 +/- 0.24 (p = 0.001), respectively. ET-1 significantly decreased the Lp to 1.99 +/- 0.48 after activation with ATP (p = 0.004). ET-1 also decreased the Lp to 1.10 +/- 0.19 after activation with bradykinin (p = 0.001). Units for Lp are x10(-7) cm x s(-1) x cm H2O(-1).

CONCLUSION

In this model, ET-1 attenuated the increase in microvascular permeability that can be seen in inflamed vessels. In addition to its vasopressor function, ET-1 may be of benefit in pathophysiologic states by decreasing third-space fluid loss. This receptor-mediated function of ET-1 may be amenable to pharmacologic manipulation.

FLOW MOTION IN THE INTESTINAL VILLI DURING HEMORRHAGIC SHOCK: A NEW METHOD TO CHARACTERIZE THE MICROCIRCULATORY CHANGES

Conventional parameters are often inadequate to describe the dynamic flow changes in microcirculation. We used a novel approach to characterize oscillatory flow conditions in a canine model of hemorrhagic shock. Microcirculation in the ileal mucosal villi was visualized using intravital microscopy with the orthogonal polarization spectral imaging technique. The distribution of red blood cell velocity (RBCV) was estimated from the relative time periods of observed RBCV, and the average RBCV (A-RBCV) and its SD were then computed from the first and second moments of the RBCV distribution, respectively. Hemorrhagic shock (for 60 min) was followed by resuscitation with saline, hypertonic saline-Dextran solution (HSD, 7.2% NaCl-10% Dextran, 4 mL/kg), or HSD supplemented with the selective endothelin-A receptor antagonist ETR-p1/fl peptide (100 nmol/kg), respectively. The macrohemodynamic derangement (70% decrease in cardiac index and ileal blood flow) during shock was associated with the appearance of flow motion in the villi and an enhanced endothelin-1 release. The calculated A-RBCV was decreased by 40%. At resuscitation onset, continuous flow periods were transiently seen in 33%, 40%, and 50% of the experiments after saline, HSD, and HSD + ETR p1/fl treatment, respectively. HSD with or without endothelin-A antagonist treatment resulted in an increased relative duration of high-flow periods (by 20%) and a significant, 20% to 40% rise in A-RBCV. These results demonstrate that time-wise variability of RBCV should be used for the analysis of oscillatory flow conditions. The probabilistic estimation of A-RBCV provides a quantitative basis for comparison of the effectiveness of different resuscitation or vasoactive strategies.

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.

Effect of estradiol administration on splanchnic perfusion after trauma-hemorrhage and sepsis

PURPOSE OF REVIEW

This review focuses on the latest mechanistic understanding of the effects of estradiol on the splanchnic circulation and the possibility of estradiol treatment as an adjunct for the treatment of trauma-hemorrhage and sepsis.

RECENT FINDINGS

Systemic hypotension induced by shock accompanies marked alterations in blood flow to various organs. Decreased splanchnic perfusion is frequently observed after insults, such as severe hemorrhage or sepsis, which leads to the destruction of the intestinal mucosal barrier and hepatic dysfunction. Studies suggest that estradiol acts as a facilitator of the intestinal blood flow via the increased production of nitric oxide, decreased production of vasoconstrictors, attenuated neutrophil adhesion, and decreased formation of oxygen free radicals.

SUMMARY

Trauma-hemorrhage results in decreased circulating blood volume. In contrast, sepsis is an inflammatory state mainly mediated by bacterial products. However, these divergent insults show similar pathophysiologic alterations in terms of the splanchnic circulation. Because estradiol effectively protects the organs from circulatory failure after various adverse circulatory conditions, many studies are being performed to clarify the molecular mechanism of estradiol action with regard to tissue circulation. Estradiol improves the macro- and microcirculation of the splanchnic organs by multiple mechanisms. Nonetheless, it remains unclear which mechanism plays the most important role in the treatment of trauma-hemorrhage and sepsis. Additional studies are required to elucidate the precise mechanism of estradiol action and to determine the usefulness of estradiol treatment for severe hemorrhage and sepsis in patients.

Role of endothelin ET(A)- and ET(B)-receptors in haemodynamic compensation following haemorrhage in anaesthetized rats

1. This study examined the role of endothelin ET(A) and ET(B) receptors on haemodynamic compensation following haemorrhage (-17.5 ml kg(-1)) in thiobutabarbitone-anaesthetized rats. Rats were divided into four groups (n=6 each): time-control, haemorrhage-control, haemorrhage after treatment with FR 139317 (ET(A)-receptor antagonist), and haemorrhage after treatment with BQ-788 (ET(B)-receptor antagonist). 2. In the time-control rats, there were no significant changes in any haemodynamics for the duration of the experiments. Relative to the time-control rats, rats given haemorrhage had reduced mean arterial pressure (MAP), cardiac output (CO) and mean circulatory filling pressure (MCFP), but increased systemic vascular resistance (R(SV)). Venous resistance (R(V)) was slightly (but insignificantly) reduced by haemorrhage. MAP, however, gradually returned towards baseline (-17+/-4 and -3+/-2 mmHg at 10 and 60 min after haemorrhage, respectively) as a result of a further increase in R(SV). 3. Pre-treatment with FR 139317 (i.v. 1 mg kg(-1), followed by 1 mg kg(-1) h(-1)) accentuated haemorrhage-induced hypotension through abolition of the increase in R(SV). FR 139317 did not modify haemorrhage-induced changes in CO, MCFP and R(V). 4. Pre-treatment of BQ-788 (3 mg kg(-1)) did not affect MAP or MCFP following haemorrhage; however, CO was lower, and R(SV) as well as R(V) were higher relative to the readings in the haemorrhaged-control rats. 5. These results show that following compensated haemorrhage, ET maintains arterial resistance and blood pressure via the activation of ET(A) but not ET(B) receptors.

Endothelin-1 blockade corrects mesenteric hypoperfusion in a porcine low cardiac output model

OBJECTIVE

To study the importance of endothelin-1-induced vasoconstriction in a model of acute and maintained low cardiac output, by investigating regional changes within the mesenteric and particularly the intestinal mucosal circulation.

DESIGN

Prospective, controlled animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Thirteen fasted, anesthetized, mechanically ventilated landrace pigs.

MEASUREMENTS AND MAIN RESULTS

Cardiac output, portal venous blood flow, renal arterial flow, jejunal mucosal microcirculation by laser Doppler flowmetry, jejunal capnotonometry (Pco2 gap), and jejunal mucosal oxygenation (tPo2) were monitored. Cardiac tamponade was established to reduce portal venous blood flow to a preset end point at two thirds of baseline. Measurements were made at baseline, after 90 mins of cardiac tamponade, and 90 mins after the administration of the combined endothelinA/endothelinB antagonist tezosentan at 1 mg.kg-1.hr-1 during tamponade in seven animals. Six animals served as time controls and received only the vehicle. Cardiac tamponade decreased portal venous blood flow, renal arterial flow, and laser Doppler flowmetry, whereas the Pco2 gap increased. The change in tPo2 failed to gain statistical significance (p =.08). Administration of tezosentan during tamponade restored portal venous blood flow and laser Doppler flowmetry to baseline values, increased tPo2 above baseline, and decreased Pco2 gap. No effect on renal arterial flow was observed. Investigated variables remained unchanged in control animals after induction of cardiac tamponade.

CONCLUSIONS

Endothelin-1 blockade in acute cardiac failure improves mesenteric, but not renal, perfusion, illustrating the regional importance of endothelin-1-induced vasoconstriction. Importantly, endothelin-1 blockade restored mucosal blood flow and oxygenation, which might be particularly interesting considering the implications for maintenance of mucosal barrier integrity in low output states.

Basal release of endothelin-1 and the influence of the ETB receptor on single vessel hydraulic permeability

BACKGROUND

Endothelin-1 (ET-1) has a direct permeability decreasing effect on the microvasculature. The present study was designed to test the hypothesis that this effect is mediated via the endothelin B (ETB) receptor located on the microvascular endothelium and to determine whether basal microvascular permeability is dependent on constitutive release of ET-1. To isolate the direct effect of ET-1, experiments were conducted under conditions in which hydraulic and oncotic pressures were controlled.

METHODS

Postcapillary venules in the rat mesentery were perfused in situ, and paired measurements of hydraulic permeability (Lp) were obtained using the modified Landis micro-occlusion method. Lp measured after a 15-minute perfusion with the ETB receptor blocker BQ-788 (1 micromol/L) was compared with measures of Lp obtained after perfusion with a combined mixture of BQ-788 and ET-1 (80 pmol/L) (n = 6). In addition, the effect of basal endogenous ET-1 was tested by measuring the effects of BQ-788 perfusion on Lp (n = 6).

RESULTS

Units for Lp are mean +/- SE x 10(-8) cm x s(-1) cm H2O(-1). ETB receptor blockade prevented any decrease in Lp induced by ET-1 (BQ-788 alone = 7.9 +/- 0.7; BQ-788 + ET-1 = 8.2 +/- 0.8;p = 0.5). Under basal conditions and in the absence of exogenous ET-1, ETB receptor blockade led to a significant increase in Lp from 6.8 +/- 0.9 to 9.7 +/- 1.2 (p = 0.001).

CONCLUSION

Decreases in microvascular permeability in single postcapillary venules after the administration of ET-1 are mediated via the ETB receptor. Constitutive release of ET-1 from the microvascular endothelium also plays a role in maintaining basal levels of permeability. These findings suggest important roles for ET-1 in maintaining and modulating microvascular permeability.

Differentiation of the peptidergic vasoregulatory response to standardized splanchnic hypoperfusion by acute hypovolaemia or sepsis in anaesthetized pigs

This study was performed to integratively investigate the vasoregulatory response during standardized splanchnic hypoperfusion in pigs. Splanchnic perfusion was reduced to 50% of baseline by: haemorrhage by 20 and 40% of the estimated total blood volume; femoral venous infusion of live E. coli to establish sepsis of systemic origin; portal venous infusion of live E. coli to establish sepsis of splanchnic origin. Invasive haemodynamic monitoring and radioimmunoassay analyses of arterial plasma concentrations of angiotensin II, endothelin-1 and atrial natriuretic peptide were carried out. Acute hypovolaemia reduced systemic and splanchnic vascular resistances following transient increases and increased angiotensin II levels (+587%), whereas endothelin-1 and atrial natriuretic peptide levels did not change significantly. Systemic sepsis following femoral venous infusion of E. coli resulted in increased splanchnic vascular resistance and increased levels of angiotensin II (+274%), endothelin-1 (+134%) and atrial natriuretic peptide (+185%). Infusion of E. coli via the portal venous route induced an increase in splanchnic vascular resistance associated with particularly elevated levels of angiotensin II (+1770%) as well as increased endothelin-1 (+201%) and atrial natriuretic peptide (+229%) concentrations. Hypovolaemia and sepsis, although standardized with a predefined level of splanchnic hypoperfusion, elicited differentiated cardiovascular and vasopeptidergic responses. Sepsis, particularly of portal origin, notably increased splanchnic vascular resistance related to increased production of the vasoconstrictors angiotensin II and endothelin-1. The role of atrial natriuretic peptide as a vasodilator seems to be of subordinate importance in hypovolaemia and sepsis.

Endothelin-1 and endothelin-4 stimulate monocyte production of cytokines

OBJECTIVE

To determine the effect of endothelin-1 and endothelin-4 on human monocyte production of cytokines.

DESIGN

Previous work from our laboratory has shown that endothelin-1 activates leukocytes. Endothelin-1 and endothelin-3 are principally produced by vascular endothelium. However, epidermal cells in gut mucosa, lung, and kidney produce endothelin-2 and endothelin-4, which differ by a single amino acid. While structurally similar to endothelin-1, endothelin-2 and endothelin-4 may affect gut smooth muscle and other tissues differently. The effect of endothelin-1 and endothelin-4 was examined on monocyte production of interleukins (IL) and neutrophil activation factors.

SETTING

A clinically-oriented basic science laboratory in a Veterans Administration Hospital and Medical Center.

SUBJECTS

Healthy volunteer adult male/female medical students, researchers, and hospital workers.

INTERVENTIONS

Human peripheral blood mononuclear cells were separated on density gradients and cultured in media, with or without the addition of bacterial endotoxin or varying molar concentrations of endothelin-1 and endothelin-4. Supernatants were harvested at 10 mins, and at 1, 6, 12, 24, and 48 hrs, and enzyme-linked immunosorbent assays were performed to determine the presence of tumor necrosis factor-alpha, IL-1 beta, IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor.

MEASUREMENTS AND MAIN RESULTS

Endothelin-1 and endothelin-4 were potent stimuli for monocyte production of tumor necrosis factor-alpha, IL-8, and granulocyte-macrophage colony-stimulating factor. They also caused IL-1 beta and IL-6 production.

CONCLUSIONS

Endothelin-1 and endothelin-4 may activate leukocytes after shock or gut ischemia, resulting in further injury to reperfused tissues and distant injury to lungs and other organs.

Effects of endothelin-1 on arterial and venous resistances in anaesthetized rats

The effects of endothelin-1 and vehicle (0.9% NaCl) on mean arterial pressure, heart rate, mean circulatory filling pressure, systemic arterial resistance, cardiac output and venous resistance were studied in four groups of pentobarbitone-anaesthetized rats, either in presence or absence of phentolamine. I.v. bolus injections of endothelin-1 at 0.5, 1 and 2 nmol/kg dose dependently increased mean arterial pressure (22, 34 and 40 mmHg), arterial resistance (33, 93 and 122% over baseline), venous resistance (40, 117 and 143% over baseline) and mean circulatory filling pressure (1.0, 1.7 and 1.8 mmHg), but decreased heart rate (-16, -21 and -17 beats/min) and cardiac output (-6, -28 and -35% below baseline). The vehicle did not significantly alter any of these variables. During the continuous infusion of phentolamine (300 microg/kg per min), endothelin-1 caused similar increases in arterial resistance, venous resistance and mean circulatory filling pressure, similar reduction in cardiac output but significantly greater pressor and bradycardic responses, suggesting that the arterial and venous constrictor effects of endothelin-1 are not due to sympathetic activation and the stimulation of alpha-adrenoceptors. The results show that endothelin-1 raised mean arterial pressure via the increment in systemic arterial resistance, since cardiac output was markedly reduced. This decrease in cardiac output was mediated by increases in arterial as well as venous resistances. The vasoconstrictor and venoconstrictor effects of endothelin-1 were independent of sympathetic tone.

Effect of extracorporeal shockwave lithotripsy on plasma and urine endothelin concentrations

Since the first reports of extracorporeal shockwave lithotripsy (SWL), there have been increasing numbers of articles in the literature documenting renal blood flow impairment and blood pressure elevation as complications. However, little is known about the pathophysiology and prevention of these complications. In this prospective study, the influence of high-energy shockwaves on plasma and urine endothelin concentrations was investigated in 20 patients with renal stones. The patients were randomly assigned to receive a calcium channel blocker, 10 mg of nitrendipine (Bypress; Bayer) (N = 10) 2 hours before SWL or no medication (control group; N = 10). Blood samples were taken just before and 1 minute after application of 3000 shocks. Urine samples were collected by ureteral catheters. The plasma endothelin-1 concentrations were significantly elevated after SWL in the control group (P = 0.003). On the other hand, nitrendipine significantly reduced plasma endothelin concentrations after SWL (P = 0.003). No significant change was observed in urine samples and blood pressure measurements. These results suggest that endothelin release after SWL may be a cause for lithotripsy-induced hemodynamic changes. Medical prevention with calcium channel blockers warrants further investigation.

Hemorrhagic shock

A great deal has been learned about the pathophysiologic condition of hemorrhagic shock. The response of the hormonal and inflammatory mediator systems in patients in hemorrhagic shock appears to represent a distinct set of responses different from those of other forms of shock. The classic neuroendocrine response to hemorrhage attempts to maintain perfusion to the heart and brain, often at the expense of other organ systems. This intense vasoconstriction occurs via central mechanisms. The response of the peripheral microcirculation is driven by local tissue hypoperfusion that results in vasodilation in the ischemic tissue bed. Activation of the systemic inflammatory response by hemorrhage and tissue injury is an important component of the pathophysiologic condition of hemorrhagic shock. Activators of this systemic inflammatory response include ischemia/reperfusion injury and neutrophil activation. Capillary "no-flow" with prolonged ischemia and "no-reflow" with reperfusion may initiate neutrophil activation in patients in hemorrhagic shock. The mechanisms that lead to decompensated and irreversible hemorrhagic shock include (1) "arteriolar hyposensitivity" as manifested by progressive arteriolar vasodilation and decreased responsiveness of the microcirculation to alpha-agonists, and (2) cellular injury and activation of both proinflammatory and counterinflammatory mechanisms. These changes represent a failure of the microcirculation. Redistribution of cardiac output and persistent gut ischemia after adequate resuscitation may also contribute to the development of irreversible hemorrhagic shock. Treatment of hemorrhagic shock includes rapid operative resuscitation to limit activation of the mediator systems and abort the microcirculatory changes that result from hemorrhagic shock. Volume resuscitation and control of hemorrhage, should occur simultaneously. The end point in volume resuscitation of hemorrhagic shock must be maintenance of organ system and cellular function. Whether we use adequate urine output, correction of lactic acidemia, optimization of oxygen delivery, or oxygen consumption as our specific goal, the general objective is to provide adequate crystalloid solution and packed red blood cells to achieve and maintain normal organ and cellular perfusion and function.