Update on hepatorenal Syndrome: Definition,Pathogenesis, and management

Hepatorenal syndrome (HRS) is acute kidney injury (AKI) that occurs without evidence of structural abnormalities in the kidneys in patients with liver disease. It is thought to be due to splanchnic vasculature dilatation that is associated with intense increase of renal arteries’ tone, leading to renal cortex ischemia and AKI. Nitric oxide, endotoxins, neurohormonal changes, bacterial infection, high serum bilirubin and bile acids are examples for factors contributing to HRS development. Nevertheless, other unknown factors may have role in HRS pathophysiology. Hence, further discussion and research are needed to clearly understand HRS. Plasma volume restoration and vasoconstrictors are the cornerstone of HRS treatment. Others such as octreotide, noradrenaline, infection control, systemic inflammatory response prevention, shunting, and renal replacement therapy are currently used to manage HRS. Liver or combined liver and kidney transplantation is currently the ultimate cure for HRS. This review was written to help in better understanding the pathogenesis, diagnosis, and treatment options for HRS.     

Hypertension enhances Aβ-induced neurovascular dysfunction,promotes β-secretase activity,and leads to amyloidogenic processing of APP

Hypertension (HTN) doubles the risk of Alzheimer’s disease (AD), but the mechanisms remain unclear. Amyloid-β (Aβ), a key pathogenic factor in AD, induces cerebrovascular dysfunction. We hypothesized that HTN acts in concert with Aβ to amplify its deleterious cerebrovascular effects and to increase Aβ production. Infusion of angiotensin II (ANGII; intravenously) elevated blood pressure and attenuated the cerebral blood flow (CBF) response to whisker stimulation or the endothelium-dependent vasodilator acetylcholine (ACh) (P < 0.05). Neocortical application of Aβ in mice receiving ANGII worsened the responses to ACh (P < 0.05). The cerebrovascular dysfunction observed in Tg2576 mice, in which Aβ is elevated both in blood and in brain due to expression of mutated amyloid precursor protein (APP), was not aggravated by neocortical application of ANGII or by a 2-week administration of ‘slow pressor’ of ANGII (600 ng/kg per minute; subcutaneously). In contrast, ANGII aggravated the dysfunction in TgSwDI mice, in which Aβ is increased only in brain. Slow-pressor ANGII induced microvascular amyloid deposition in Tg2576 mice and enhanced β-secretase APP cleavage. In Chinese hamster ovary (CHO) cells producing Aβ, ANGII increased β-secretase activity, Aβ1–42, and the Aβ42/40 ratio. We conclude that HTN enhances amyloidogenic APP processing, effects that may contribute to the pathogenic interaction between HTN and AD.     

高血压患者内皮脂肪酶与肱动脉血流介导的内皮依赖性血管舒张功能的关系

目的观察高血压患者内皮脂肪酶(EL)的变化,并探讨其与肱动脉血流介导的内皮依赖性血管舒张功能(FMD)的关系。方法入选初诊原发性高血压(EH)患者(EH组,n=132)和血压正常的健康体检者(对照组,n=118)为受试者,测量两组研究对象的身高、体质量、血压,检测空腹血糖、总胆固醇、三酰甘油、低密度脂蛋白胆固醇(LDL-C)和高密度脂蛋白胆固醇(HDL-C),用酶联免疫吸附法检测血浆EL的水平,用超声技术检测FMD,分析EL与FMD的相关性。结果EH组血浆EL水平明显高于对照组[(468.3±50.7)比(235.0±24.9)μg/L,P<0.05],FMD显著低于对照组[(7.2±2.1)%比(12.3±2.4)%,P<0.05],而且,随着高血压分级的增加,EL水平逐步升高,但是FMD逐渐下降(趋势均P<0.05)。对EH组进行Pearson相关分析显示FMD与收缩压、舒张压、体质量指数(BMI)、空腹血糖、总胆固醇、三酰甘油、LDL-C和EL呈负相关,与HDL-C呈正相关(均P<0.05)。多元线性逐步回归显示,校正年龄、性别、血压、血脂、血糖等因素后,EL是FMD的影响因素(P<0.05)。结论高血...     

单纯收缩期高血压患者血清晚期糖基化终产物与血管功能的关系

目的探讨晚期糖基化终末产物(AGEs)与血流介导的内皮依赖性血管舒张功能(FMD)间的关系及其致血管功能异常的作用。方法选择单纯收缩期高血压(ISH)患者120例作为ISH组,双期高血压患者120例作为双期高血压(DH)组,年龄配对的健康人群70例作为正常对照组,采用日本科林公司生产的VP1000动脉硬化检测仪测定颈股动脉脉搏波传导速度(cfPWV),超声技术测定FMD,ELISA检测受试者外周血清中AGEs和内皮素1,Griess法测定外周血中一氧化氮含量。结果ISH组的cfPWV、AGEs、内皮素1高于DH组及正常对照组(P<0.05);ISH组及DH组FMD、一氧化氮低于正常对照组(P<0.05),而FMD、一氧化氮在ISH组及DH组间差异无统计学意义;AGEs与cfPWV、内皮素1呈正相关(r=0.525,P<0.01;r=0.863,P<0.01);AGEs与FMD、一氧化氮呈负相关(r=-0.635,P<0.01;r=-0.669,P<0.01);多元逐步回归分析显示AGEs、cfPWV是FMD的危险因素。结论AGEs是导致血管功能异常的危险因素,可能在ISH的发生发展过程中起一定作用。     

MEASUREMENT OF PULMONARY FLOW RESERVE IN HIGHER PRIMATES

• 1 There are currently limited diagnostic methods for assessing the integrity of the pulmonary microvasculature. We hypothesized that a novel, invasively determined physiological index of ‘pulmonary flow reserve’ (PFR = maximal hyperaemic pulmonary blood flow divided by basal pulmonary flow) may facilitate microvascular assessment in the lung. Therefore, we developed a baboon model in which to: (i) validate the use of Doppler flow velocity for PFR assessment; (ii) define the optimal drug and dose regimen for attainment of maximal pulmonary hyperaemia; and (iii) demonstrate the feasibility of measuring PFR in healthy higher primates.
• 2 Doppler sensor guidewires were placed in segmental pulmonary arteries of 11 ketamine‐anaesthetized baboons. Vessel diameter, flow velocity and haemodynamics were recorded before and after direct intrapulmonary artery administration of saline, adenosine (50–500 µg/kg per min) and papaverine (3–60 mg), enabling calculation of PFR.
• 3 Saline (either bolus injection or infusion) did not alter vessel diameter or flow velocity (P > 0.1), validating local drug administration. Both adenosine and papaverine induced dose‐dependent increases in flow velocity from baseline (from 22.5 ± 2.3 to 32.7 ± 4.8 cm/s for 400–500 µg/kg per min adenosine; and from 23.9 ± 1.1 to 34.6 ± 4.0 cm/s for 24 mg papaverine; both P < 0.0001), without affecting pulmonary artery pressure or vessel diameter (P > 0.3). Healthy primate PFR values were 1.35 ± 0.10 and 1.39 ± 0.10 using 200 µg/kg per min adenosine and 24 mg papaverine, respectively (P > 0.8).
• 4 In conclusion, pulmonary flow reserve in higher primates can be assessed using Doppler sensor guidewire and either adenosine or papaverine as microvascular hyperaemic agents. Measurements of PFR may facilitate pulmonary microvascular assessments.

     

Morphine is an arteriolar vasodilator in man

AIM

The mechanisms of action of morphine on the arterial system are not well understood. The aim was to report forearm vascular responses, and their mediation, to intra-arterial morphine in healthy subjects.

METHODS

Three separate protocols were performed: (i) dose ranging; (ii) acute tolerance; (iii) randomized crossover mechanistic study on forearm blood flow (FBF) responses to intrabrachial infusion of morphine using venous occlusion plethysmography. Morphine was infused either alone (study 1 and 2), or with an antagonist: naloxone, combined histamine-1 and histamine-2 receptor blockade or during a nitric oxide clamp.

RESULTS

Morphine caused an increase in FBF at doses of 30 µg min⁻¹[3.25 (0.26) ml min⁻¹ 100 ml⁻¹][mean (SEM)] doubling at 100 µg min⁻¹ to 5.23 (0.53) ml min⁻¹ 100 ml⁻¹. Acute tolerance was not seen to 50 µg min⁻¹ morphine, with increased FBF [3.96 (0.35) ml min⁻¹ 100 ml⁻¹] (P = 0.003), throughout the 30-min infusion period. Vasodilatation was abolished by pretreatment with antihistamines (P = 0.008) and the nitric oxide clamp (P < 0.001), but not affected by naloxone. The maximum FBF with pretreatment with combined H1/H2 blockade was 3.06 (0.48) and 2.90 (0.17) ml min⁻¹ 100 ml⁻¹ after 30 min, whereas with morphine alone it reached 4.3 (0.89) ml min⁻¹ 100 ml⁻¹.

CONCLUSIONS

Intra-arterial infusion of morphine into the forearm circulation causes vasodilatation through local histamine-modulated nitric oxide release. Opioid receptor mechanisms need further exploration.     

Activation of iGluR5 kainate receptors inhibits neurogenic dural vasodilatation in an animal model of trigeminovascular activation

Background and purpose:

Migraine is a disabling neurological disorder involving activation, or the perception of activation, of trigeminovascular afferents containing calcitonin gene-related peptide (CGRP). Released CGRP from peripheral trigeminal afferents causes dilatation of dural blood vessel, and this is used to measure trigeminal nerve activation. Kainate receptors with the GluR5 subunit (iGluR5, ionotropic glutamate receptor) are present in the trigeminal ganglion and may be involved in nociception. We investigated the possible involvement of prejunctional iGluR5 kainate receptors on CGRP release from trigeminal afferents.

Experimental approach:

We used neurogenic dural vasodilatation, which involves reproducible vasodilatation in response to CGRP release after electrical stimulation of the dura mater surrounding the middle meningeal artery. The effects of the specific iGluR5 receptor antagonist UBP 302 and agonist (S)-(-)-5-iodowillardiine were investigated on neurogenic and CGRP-induced dural vasodilatation in rats, by using intravital microscopy.

Key results:

Administration of 10 and 20 mg·kg⁻¹ of iodowillardiine inhibited electrically induced dural vessel dilatation, an effect blocked by pretreatment with 50 mg·kg⁻¹ UBP 302. Administration of the iGluR5 receptor antagonist UBP 302 alone had no significant effect. CGRP (1 mg·kg⁻¹)-induced dural vasodilatation was not inhibited by the iGluR5 receptor agonist iodowillardiine.

Conclusions and implications:

This study demonstrates that activation of the iGluR5 kainate receptors with the selective agonist iodowillardiine is able to inhibit neurogenic dural vasodilatation probably by inhibition of prejunctional release of CGRP from trigeminal afferents. Taken together with recent clinical studies the data reinforce CGRP mechanisms in primary headaches and demonstrate a novel role for kainate receptor modulation of trigeminovascular activation.     

The ecto-nucleotidase NTPDase1 differentially regulates P2Y1 and P2Y2 receptor-dependent vasorelaxation

Background and purpose:

Extracellular nucleotides produce vasodilatation through endothelial P2 receptor activation. As these autacoids are actively metabolized by the ecto-nucleotidase nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), we studied the effects of this cell surface enzyme on nucleotide-dependent vasodilatation.

Experimental approach:

Vascular NTPDase expression and activity were evaluated by immunohistochemistry and histochemistry. The vascular effects of nucleotides were tested in vivo by monitoring mean arterial pressure, and in vitro comparing reactivity of aortic rings using wild-type and Entpd1^−/− (lacking NTPDase1) mice.

Key results:

The absence of NTPDase1 in Entpd1^−/− mice led to a dramatic drop in endothelial nucleotidase activity. This deficit was associated with an exacerbated decrease in blood pressure after nucleotide injection. Following ATP injection, mean arterial pressure was decreased in Entpd1^+/+ and Entpd1^−/− mice by 5.0 and 17%, respectively, and by 0.1 and 19% after UTP injection (10 nmole·kg⁻¹ both). In vitro, the concentration-response curves of relaxation to ADP and ATP were shifted to the left, revealing a facilitation of endothelial P2Y1 and P2Y2 receptor activation in Entpd1^−/− mice. EC₅₀ values in Entpd1^+/+ versus Entpd1^−/− aortic rings were 14 µM versus 0.35 µM for ADP, and 29 µM versus 1 µM for ATP. In Entpd1^−/− aortas, P2Y1 receptors were more extensively desensitized than P2Y2 receptors. Relaxations to the non-hydrolysable analogues ADPβS (P2Y1) and ATPγS (P2Y2) were equivalent in both genotypes confirming the normal functionality of these P2Y receptors in mutant mice.

Conclusions and implications:

NTPDase1 controls endothelial P2Y receptor-dependent relaxation, regulating both agonist level and P2 receptor reactivity.     

The Role of Potassium Channels in Relaxant Effect of Levosimendan in Rat Small Mesenteric Arteries

Summary We investigated both the effect of levosimendan and the role of various potassium channels in KCl-precontracted rat small mesenteric arteries. Levosimendan (10⁻⁶−10⁻³ M) or cromakalim (CRO, 10⁻⁷−10⁻⁴ M) produced concentration-dependent relaxation responses in small mesenteric arteries precontracted by 30 mM KCl. The relaxant responses to levosimendan in KCl-precontracted arteries did not differ significantly between endothelium-intact and endothelium-denuded preparations. Incubation of rat small mesenteric arterial segments with ATP-dependent potassium channel (KATP) blocker glibenclamide (GLI, 10⁻⁶ M) for 30 min significantly inhibited the relaxant responses to both levosimendan and CRO. Neither the Ca²⁺-activated potassium channel (KCa) blocker iberiotoxin (10⁻⁷ M) nor the voltage-dependent potassium channel (KV) blocker 4-aminopyridine (5 mM) incubation for 30 min caused significant alterations in relaxant responses to levosimendan in KCl-precontracted small mesenteric arteries. These findings suggested that levosimendan-induced relaxation responses in isolated rat small mesenteric arteries were neither depended on endothelium nor inhibited by the blockers of KV or KCa but, they rather seem to depend on the activation of KATP.     

乳内动脉M1胆碱能受体功能的研究

目的：探讨乳内动脉M1胆碱能受体的特性,以离体人乳内动脉为模型,进行收缩功能的实验。方法：取21例行CABG患者内皮完整的离体乳内动脉血管段根据应用拮抗剂处理的不同,随机分为阿托品组、M1受体拮抗剂（哌仑西平）组、M2受体拮抗剂（美索曲平）组。应用受体功能分析法对乳内动脉M1胆碱能受体亚型的功能进行研究。结果：发现在人乳内动脉中,M1胆碱能受体和M2胆碱能受体均可介导其舒张反应并以M1胆碱能受体为主。结论：在离体人乳内动脉上存在功能性M及M胆碱能受体,M胆碱能受体的最大舒张反应远远小于M胆碱能受体。