Effect of angiotensin II and endothelin-1 receptor blockade on the haemodynamic and hormonal changes after acute blood loss and after retransfusion in conscious dogs

Local gastric RAAS inhibition improves gastric microvascular perfusion in dogs

During circulatory shock, gastrointestinal microcirculation is impaired, especially via activation of the renin-angiotensin-aldosterone system. Therefore, inhibition of the renin-angiotensin-aldosterone system might be beneficial in maintaining splanchnic microcirculation. The aim of this study was to analyze whether locally applied losartan influences gastric mucosal perfusion (µflow, µvelo) and oxygenation (µHbO2) without systemic hemodynamic changes. In repetitive experiments six anesthetized dogs received 30 mg losartan topically on the oral and gastric mucosa during normovolemia and hemorrhage (-20% blood volume). Microcirculatory variables were measured with reflectance spectrometry, laser Doppler flowmetry and incident dark field imaging. Transpulmonary thermodilution and pulse contour analysis were used to measure systemic hemodynamic variables. Gastric barrier function was assessed via differential absorption of inert sugars. During normovolemia, losartan increased gastric µflow from 99 ± 6 aU to 147 ± 17 aU and µvelo from 17 ± 1 aU to 19 ± 1 aU. During hemorrhage, losartan did not improve µflow. µvelo decreased from 17 ± 1 aU to 14 ± 1 aU in the control group. Application of losartan did not significantly alter µvelo (16 ± 1 aU) compared to the control group and to baseline levels (17 ± 1 aU). No effects of topical losartan on macrohemodynamic variables or microcirculatory oxygenation were detected. Gastric microcirculatory perfusion is at least partly regulated by local angiotensin receptors. Topical application of losartan improves local perfusion via vasodilation without significant effects on systemic hemodynamics. During mild hemorrhage losartan had minor effects on regional perfusion, probably because of a pronounced upstream vasoconstriction.

Angiotensin II Type 1 Receptors and Systemic Hemodynamic and Renal Responses to Stress and Altered Blood Volume in Conscious Rabbits

We examined how systemic blockade of type 1 angiotensin (AT(1)-) receptors affects reflex control of the circulation and the kidney. In conscious rabbits, the effects of candesartan on responses of systemic and renal hemodynamics and renal excretory function to acute hypoxia, mild hemorrhage, and plasma volume expansion were tested. Candesartan reduced resting mean arterial pressure (MAP, -8 ± 2%) without significantly altering cardiac output (CO), increased renal blood flow (RBF, +38 ± 9%) and reduced renal vascular resistance (RVR, -32 ± 6%). Glomerular filtration rate (GFR) was not significantly altered but sodium excretion (U(Na+)V) increased fourfold. After vehicle treatment, hypoxia (10% inspired O(2) for 30 min) did not significantly alter MAP or CO, but reduced heart rate (HR, -17 ± 6%), increased RVR (+33 ± 16%) and reduced GFR (-46 ± 16%) and U(Na+)V (-41 ± 17%). Candesartan did not significantly alter these responses. After vehicle treatment, plasma volume expansion increased CO (+35 ± 7%), reduced total peripheral resistance (TPR, -26 ± 5%), increased RBF (+62 ± 23%) and reduced RVR (-32 ± 9%), but did not significantly alter MAP or HR. It also increased U(Na+)V (803 ± 184%) yet reduced GFR (-47 ± 9%). Candesartan did not significantly alter these responses. After vehicle treatment, mild hemorrhage did not significantly alter MAP but increased HR (+16 ± 3%), reduced CO (-16 ± 4%) and RBF (-18 ± 6%), increased TPR (+18 ± 4%) and tended to increase RVR (+18 ± 9%, P = 0.1), but had little effect on GFR or U(Na+)V. But after candesartan treatment MAP fell during hemorrhage (-19 ± 1%), while neither TPR nor RVR increased, and GFR (-64 ± 18%) and U(Na+)V (-83 ± 10%) fell. AT(1)-receptor activation supports MAP and GFR during hypovolemia. But AT(1)-receptors appear to play little role in the renal vasoconstriction, hypofiltration, and antinatriuresis accompanying hypoxia, or the systemic and renal vasodilatation and natriuresis accompanying plasma volume expansion.

Medium on-treatment platelet reactivity to ADP is favorable in patients with acute coronary syndromes undergoing coronary stenting

Bleeding in the setting of acute coronary syndromes (ACS) has negative prognostic implications. We sought to determine the impact of different levels of on-treatment platelet reactivity (PR) to ADP on both bleeding and ischemic events in ACS patients receiving coronary stenting. PR to ADP was measured with the VerifyNow P₂Y₁₂ assay (Accumetrics, San Diego, CA) in 374 patients with ACS receiving standard dual antiplatelet therapy. Patients were stratified into three tertiles according to the increasing values of P₂Y₁₂ reaction units with the first tertile defined as low, second as medium, and third as high PR. The end points were bleeding (TIMI major or minor), ischemic end point (cardiovascular death and non-fatal myocardial infarction), and combined end point (bleeding or ischemic end point). At 30 days: low PR was associated with increased risk of bleeding as compared to medium (adjusted hazard ratio [HR] 3.50, 95% confidence intervals (CI) 1.30-9.42, p = 0.013) and high PR (HR 2.78, 95% CI 1.50-5.15, p = 0.001); high PR posed increased risk of ischemic endpoint as compared with medium PR (HR 7.26, 95% CI 1.67-31.55, p = 0.008) and a trend towards higher incidence of ischemic events was observed when compared with low PR (HR 1.51, 95% CI 0.96-2.36, p = 0.074); patients with medium PR were at significantly lower risk of combined end point as compared to those with low (HR 0.30, 95% CI 0.12-0.75, p = 0.01) and high PR (HR 0.31, 95% CI 0.12-0.77, p = 0.012). In conclusion, low PR to ADP is associated with increased hazard of bleeding and poses similar combined risk of bleeding and ischemic events as high PR. Medium PR predicts favorable net outcome in ACS patients.

Endothelin receptor subtype A blockade does not affect the haemodynamic recovery from haemorrhage during xenon/remifentanil or isoflurane/remifentanil anaesthesia in dogs

OBJECTIVE

To test the compensatory role of endothelin-1 when acute blood loss is superimposed on anaesthesia, by characterizing the effect of systemic endothelin receptor subtype A (ET(A)) blockade on the haemodynamic and hormonal responses to haemorrhage in dogs anaesthetized with xenon/remifentanil (X/R) or isoflurane/remifentanil (I/R).

STUDY DESIGN

Prospective experimental randomized controlled study.

ANIMALS

Six female Beagle dogs, 13.4 +/- 1.3 kg.

METHODS

Animals were anaesthetized with remifentanil 0.5 microg kg(-1) minute(-1) plus either 0.8% isoflurane (I/R) or 63% xenon (X/R), with and without (Control) the systemic intravenous endothelin receptor subtype A antagonist atrasentan (four groups, n = 6 each). After 60 minutes of baseline anaesthesia, the dogs were bled (20 mL kg(-1)) over 5 minutes and hypovolemia was maintained for 1 hour. Continuous haemodynamic monitoring was performed via femoral and pulmonary artery catheters; vasoactive hormones were measured before and after haemorrhage.

RESULTS

In Controls, systemic vascular resistance (SVR), vasopressin and catecholamine plasma concentrations were higher with X/R than with I/R anaesthesia at pre-haemorrhage baseline. The peak increase after haemorrhage was higher during X/R than during I/R anaesthesia (SVR 7420 +/- 867 versus 5423 +/- 547 dyne seconds cm(-5); vasopressin 104 +/- 23 versus 44 +/- 6 pg mL(-1); epinephrine 2956 +/- 310 versus 177 +/- 99 pg mL(-1); norepinephrine 862 +/- 117 versus 195 +/- 33 pg mL(-1), p < 0.05). Haemorrhage reduced central venous pressure from 3 +/- 1 to 1 +/- 1 cm H(2)O (I/R, ns) and from 8 +/- 1 to 5 +/- 1 cm H(2)O (X/R, p < 0.05), but did not reduce mean arterial pressure, nor cardiac output. Atrasentan did not alter the haemodynamic and hormonal response to haemorrhage during either anaesthetic protocol.

CONCLUSIONS AND CLINICAL RELEVANCE

Selective ET(A) receptor blockade with atrasentan did not impair the haemodynamic and hormonal compensation of acute haemorrhage during X/R or I/R anaesthesia in dogs.

The haemodynamic and catecholamine response to xenon/remifentanil anaesthesia in Beagle dogs

The noble gas xenon seems to have minimal cardiovascular side-effects and so may be an ideal anaesthetic agent when investigating cardiovascular physiology. In comparison with standard modern anaesthetics, we investigated the haemodynamic and hormonal effects of xenon in Beagle dogs. After a 30 min baseline period, anaesthesia was induced with propofol and maintained with either (1) 1.2% isoflurane/70% nitrous oxide (N2O), (2) 0.8% isoflurane/0.5 µg/kg/min remifentanil or (3) 63% xenon/0.5 µg/kg/min remifentanil ( n = 6 per group). Haemodynamics were recorded and blood samples taken before and 60 min after induction. Mean arterial blood pressure (MAP) was higher in conscious dogs than during isoflurane/N2O (86 ± 2 vs. 65 ± 2 mmHg, mean ± SEM) and isoflurane/remifentanil anaesthesia (95 ± 2 vs. 67 ± 3 mmHg), whereas MAP did not decrease significantly in response to xenon/remifentanil anaesthesia (96 ± 4 vs. 85 ± 6 mmHg). Bradycardia was present during isoflurane/remifentanil (54 ± 2/min) and xenon/remifentanil (40 ± 3/min), but not during isoflurane/N2O anaesthesia (98 ± 3/min, P < 0.05). Xenon/remifentanil anaesthesia induced the highest reduction in cardiac output (CO) (–61%), and the highest increase in systemic vascular resistance (+120%) among all treatment groups ( P < 0.05). A simultaneous increase in endogenous adrenaline and noradrenaline concentrations could only be observed in the xenon/remifentanil group, whereas angiotensin II and vasopressin concentrations increased in all groups. In conclusion, xenon/remifentanil anaesthesia maintains MAP but reduces heart rate and CO and is associated with a considerable stimulation of vasopressor hormones in Beagle dogs. Therefore, xenon/remifentanil exerts a new quality of adverse haemodynamic effects different from volatile anaesthetics and may not perform better during studies of cardiovascular physiology.

ETA-receptor blockade impairs vasoconstriction after hemorrhage in xenon-anesthetized dogs treated with an AT1-receptor antagonist

The effects of endothelin receptor subtype A (ETA) blockade on hemodynamics and hormonal adaptation during hemorrhage were studied in xenon/remifentanil-anesthetized dogs (n=6) pretreated with an angiotensin II type 1 (AT1)-receptor blocker.

CONTROLS

after a baseline awake period, anesthesia was induced in the dogs with propofol and maintained with xenon/remifentanil (baseline anesthesia). Sixty minutes later, 20 mL x kg(-1) of blood was withdrawn within 5 min and the dogs observed for another hour (hemorrhage). AT1 group followed the same protocol as controls except the AT1-receptor blocker losartan (i.v. 100 microg x kg(-1) x min(-1)) was started at the beginning of the experiment. AT1+ETA group was the same as AT1 group but with the addition of the ETA-receptor blocker atrasentan (i.v. 1 mg x kg(-1), then 0.01 mg x kg(-1) x min(-1)). In controls, mean arterial pressure (MAP) remained unchanged during baseline anesthesia, whereas systemic vascular resistance (SVR) increased from 3282+/-281 to 7321+/-803 dyn.s.cm-5, heart rate (HR) decreased from 86+/-4 to 40+/-3 beats x min(-1), and cardiac output (CO) decreased from 2.3+/-0.2 to 0.9+/-0.1 L x min(-1) (p<0.05), with no further changes after hemorrhage. In AT1-inhibited dogs, MAP (71+/-6 mm Hg) and SVR (5939+/-611 dyn x s x cm(-5)) were lower during baseline anesthesia and after hemorrhage, but greater than those in AT1+ETA (66+/-7 mm Hg, 5034+/-658 dyn x s x cm(-5)) (p<0.05). HR and CO were not different between groups. Plasma concentration of vasopressin was highest with AT1+ETA inhibition after hemorrhage. Combined AT1+ETA-receptor blockade impaired vasoconstriction more than did AT1-receptor blockade alone, both during baseline xenon anesthesia and after hemorrhage. Even a large increase in vasoconstrictor hormones could not prevent the decrease in blood pressure and the smaller increase in SVR. Thus, endothelin is an important vasoconstrictor during hemorrhage, and both endothelin and angiotensin II are essential hormones for cardiovascular stabilization after hemorrhage.

The role of angiotensin II receptor-1 blockade in the hypoxic pulmonary vasoconstriction response in newborn piglets

BACKGROUND

Angiotensin-converting enzyme activity is increased in newborn infants with respiratory distress syndrome and in animals with alveolar hypoxia.

OBJECTIVE

To test whether angiotensin II (Ang II) mediates the pulmonary vasoconstriction induced by acute hypoxia in newborn piglets.

METHODS

Eight unanesthetized chronically instrumented newborn piglets (mean +/- SEM; age 6.6 +/- 0.6 days; weight 2,181 +/- 174 g) were randomly assigned to receive a saline solution or the Ang II type 1 receptor (AT(1)) antagonist, losartan, in a crossover study design, with an interval of at least 48 h between the first and second study. Pulmonary artery (Ppa), wedge, systemic arterial (Psa) and right atrial pressures, cardiac output (CO), pulmonary (PVR) and systemic (SVR) vascular resistances, and arterial blood gases were obtained in room air, before and during the saline or losartan infusion (6 mg/kg followed by 3 mg/kg/h), and during 6 h of hypoxia (FiO(2) = 0.11) and saline or losartan infusion. Data were analyzed by repeated measures analysis of variance.

RESULTS

The pulmonary vasoconstriction induced by acute hypoxia was significantly attenuated during losartan infusion, while Psa, SVR, CO, pH, PaCO(2), PaO(2) and base excess did not differ between groups. During room air, Ppa, PVR, Psa, SVR and CO values were not modified by saline or losartan infusion.

CONCLUSION

These data suggest that the pulmonary vasoconstriction induced by acute hypoxia in newborn piglets is partially mediated by Ang II, acting via AT(1).

Temporal trends in antiplatelet/antithrombotic use in acute coronary syndromes and in-hospital major bleeding complications

Antithrombotic and antiplatelet agents are essential for the management of patients with acute coronary syndromes (ACSs). These pharmacologic agents have the potential for increased risk of bleeding. It is not clear if the increased uptake of these therapies has resulted in a clinically evident increase in bleeding complications over time. In this study, we included 3,193 consecutive patients who were admitted to the University of Michigan with an ACS (unstable angina or myocardial infarction) between January 1999 and December 2004. These patients were analyzed for temporal trends in antithrombotic and antiplatelet agent use, thrombolytic therapy, cardiac catheterizations, percutaneous coronary interventions, and major bleeding complications (including gastrointestinal, vascular access, and intracranial hemorrhage). We found a decreasing temporal trend in the incidence of major in-hospital bleeding complications (p <0.001) despite an increasing use of ticlopidine/clopidogrel (p <0.0001), unfractionated heparin (p <0.01), glycoprotein IIb/IIIa inhibitors (p <0.0001), and percutaneous coronary intervention (p <0.0001) in the management of patients with ACSs. In conclusion, major bleeding remains a significant complication of ACS management but has decreased significantly over time. We believe that this decreasing bleeding trend may be because of better identification of higher risk patients, attention to correct dosing, appropriate monitoring, and incorporation of various periprocedural strategies in routine clinical practice.

Impact of bleeding severity on clinical outcomes among patients with acute coronary syndromes

Bleeding is a complication of current therapies for acute coronary syndrome (ACS). No studies have examined the effect of bleeding events on clinical outcomes. We analyzed pooled data from 4 multicenter, randomized clinical trials of patients who had ACS (n = 26,452) to determine an association between bleeding severity as measured by the GUSTO scale and 30-day and 6-month mortality rates using Cox proportional hazards modeling that incorporated bleeding as a time-dependent covariate. The analysis was repeated to examine procedure- and non-procedure-related bleeding and after censoring at the time of coronary artery bypass grafting. Of all the patients included, 27.6% had > or =1 bleeding episode. Patients who bled were older and sicker at presentation than were those who did not bleed. Unadjusted rates of 30-day and 6-month mortality increased as bleeding severity increased. There were stepwise increases in the adjusted hazards of 30-day mortality (mild bleeding, hazard ratio [HR] 1.6, 95% confidence interval [CI] 1.3 to 1.9; moderate bleeding, HR 2.7, 95% CI l 2.3 to 3.4; severe bleeding, HR 10.6, 95% CI 8.3 to 13.6) and 6-month mortality (mild bleeding, HR 1.4, 95% CI 1.2 to 1.6; moderate bleeding, HR 2.1, 95% CI 1.8 to 2.4; severe bleeding, HR 7.5, 95% CI 6.1 to 9.3) as bleeding severity increased. Results were consistent after censoring for coronary artery bypass grafting and for procedure- and non-procedure-related bleeds. In conclusion, the GUSTO bleeding classification identifies patients who are at risk for short- and long-term adverse events. Therapies that minimize bleeding risk and maintain an anticoagulant effect may improve outcomes among patients who have ACS.