Altered mesenteric venous capacitance and volume pooling in cirrhotic rats are mediated by nitric oxide

Decompensated liver cirrhosis and neural regulation of mesenteric vascular tone in rats: role of sympathetic, nitrergic and sensory innervations

We evaluated the possible alterations produced by liver cholestasis (LC), a model of decompensated liver cirrhosis in sympathetic, sensory and nitrergic nerve function in rat superior mesenteric arteries (SMA). The vasoconstrictor response to electrical field stimulation (EFS) was greater in LC animals. Alpha-adrenoceptor antagonist phentolamine and P2 purinoceptor antagonist suramin decreased this response in LC animals more than in control animals. Both non-specific nitric oxide synthase (NOS) L-NAME and calcitonin gene related peptide (CGRP) (8-37) increased the vasoconstrictor response to EFS more strongly in LC than in control segments. Vasomotor responses to noradrenaline (NA) or CGRP were greater in LC segments, while NO analogue DEA-NO induced a similar vasodilation in both experimental groups. The release of NA was not modified, while those of ATP, nitrite and CGRP were increased in segments from LC. Alpha 1 adrenoceptor, Rho kinase (ROCK) 1 and 2 and total myosin phosphatase (MYPT) expressions were not modified, while alpha 2B adrenoceptor, nNOS expression and nNOS and MYPT phosphorylation were increased by LC. Together, these alterations might counteract the increased splanchnic vasodilation observed in the last phases of decompensated liver cirrhosis.

Serial Measurements of Splanchnic Vein Diameters in Rats Using High-Frequency Ultrasound

The purpose of this study was to investigate serial ultrasound imaging in rats as a fully non-invasive method to (1) quantify the diameters of splanchnic veins in real time as an indirect surrogate for the capacitance function of those veins, and (2) assess the effects of drugs on venous dimensions. A 21 MHz probe was used on anesthetized male Sprague–Dawley rats to collect images containing the portal vein (PV), superior mesenteric vein (SMV), abdominal inferior vena cava (IVC), and splenic vein (SpV; used as a landmark in timed studies) and the abdominal aorta (AA). Stable landmarks were established that allowed reproducible quantification of cross-sectional diameters within an animal. The average diameters of vessels measured every 5 min over 45 min remained within 0.75 ± 0.15% (PV), 0.2 ± 0.09% (SMV), 0.5 ± 0.12% (IVC), and 0.38 ± 0.06% (AA) of baseline (PV: 2.0 ± 0.12 mm; SMV: 1.7 ± 0.04 mm; IVC: 3.2 ± 0.1 mm; AA: 2.3 ± 0.14 mm). The maximal effects of the vasodilator sodium nitroprusside (SNP; 2 mg/kg, i.v. bolus) on venous diameters were determined 5 min post SNP bolus; the diameters of all noted veins were significantly increased by SNP, while mean arterial pressure (MAP) decreased 29 ± 4 mmHg. By contrast, administration of the venoconstrictor sarafotoxin (S6c; 5 ng/kg, i.v. bolus) significantly decreased PV and SpV, but not IVC, SMV, or AA, diameters 5 min post S6c bolus; MAP increased by 6 ± 2 mmHg. In order to determine if resting splanchnic vein diameters were stable over much longer periods of time, vessel diameters were measured every 2 weeks for 8 weeks. Measurements were found to be highly reproducible within animals over this time period. Finally, to evaluate the utility of vein imaging in a chronic condition, images were acquired from 4-week deoxycorticosterone acetate salt (DOCA-salt) hypertensive and normotensive (SHAM) control rats. All vessel diameters increased from baseline while MAP increased (67 ± 4 mmHg) in DOCA-salt rats compared to SHAM at 4 weeks after pellet implantation. Vessel diameters remained unchanged in SHAM animals. Together, these results support serial ultrasound imaging as a non-invasive, reliable technique able to measure acute and chronic changes in the diameter of splanchnic veins in intact rats.

Blunted cardiac response to hemorrhage in cirrhotic rats is mediated by local macrophage-released endocannabinoids

BACKGROUND & AIMS

Cirrhosis is associated with blunted cardiovascular response to stimuli such as hemorrhage, but the mechanism remains unclear. We aimed to clarify the role of endocannabinoids in blunted hemorrhage response in cirrhotic rats.

METHODS

Cirrhosis was induced by bile duct ligation (BDL). Hemodynamics were measured. Cannabinoid receptor-1 (CB1) antagonist, AM251, and macrophage inhibitor gadolinium chloride (GdCl3) were administered. Myocardial levels of anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) were measured and resident monocytes and macrophages quantified by immunohistochemistry. Isolated cardiomyocyte contractility was measured before and after incubation with monocytes from BDL and sham controls.

RESULTS

Hemorrhage significantly decreased arterial pressure and left ventricular dP/dT. After hemorrhage, these changes quickly reversed in controls, but were severely prolonged in BDL rats. Chronic AM251 treatment restored this impaired response. AEA and 2-AG levels were increased in BDL hearts and further increased after hemorrhage. Sham hearts showed virtually no monocytes or macrophages before or after hemorrhage, whereas BDL hearts had significantly more white blood cells which further increased after hemorrhage. GdCl3 treatment significantly reduced cardiac endocannabinoid levels both at baseline and after hemorrhage. This treatment also restored cardiovascular response to hemorrhage in BDL rats but did not affect sham controls. Monocytes isolated from BDL rats more potently inhibited cardiomyocyte contractility than sham control monocytes.

CONCLUSIONS

The cirrhotic heart showed increased monocyte recruitment and endocannabinoid levels. CB1 blockade or GdCl3 treatment restored blunted cardiovascular response to hemorrhage. Endocannabinoids released by monocytes blunt cardiac response to hemorrhage. Preventing monocyte recruitment or blocking endocannabinoid signaling may improve cardiovascular homeostasis in cirrhosis.

Anti-VEGFR agents ameliorate hepatic venous dysregulation/microcirculatory dysfunction, splanchnic venous pooling and ascites of NASH-cirrhotic rat

BACKGROUND & AIMS

Antivascular endothelial growth factor receptor (VEGFR) agents improve hepatic fibrosis and portal hypertension in cirrhosis. Detail interactions among recruited/activated leucocytes, hepatic angiogenesis and fibrogenesis, splanchnic blood pooling, decreased hepatic veins to fluctuated splanchnic blood volume (hepatic venous dysregulation), portal hypertensive syndrome and ascites have never explored in cirrhosis. Our study used two anti-VEGFR agents - brivanib and sorafenib - to elucidate the relationship between above abnormalities of nonalcoholic steatohepatitis (NASH)-cirrhotic rats.

MATERIALS AND METHODS

NASH-cirrhotic rats received 2-week brivanib, sorafenib or vehicle (NASH-cirrhotic+briv, NASH-cirrhotic+soraf and NASH-cirrhotic rats) were included for various measurements.

RESULTS

In comparison with NASH-cirrhotic rats, significant decreased plasma VEGF, fibroblast growth factor, platelet-derived growth factor, hepatic tumour necrosis factor (TNFα), IL-1β, IL-6, IL-17 were accompanied by decreased leucocyte mass/activity ((99 m) Tc-phytate and (18) F-FDG SPECT/PET/CT scans), hepatic leucocytes recruitment/microvascular density (fluorescence-enhanced intravital microscopy) and hydroxyproline content, and increased hepatic blood flow in NASH-cirrhotic+briv and NASH-cirrhotic+soraf rats. In addition, increased hepatic microvasculatures compliance-related improved buffering effect of portal vein to acute mannitol infusion was associated with decreased circulating nitric oxide and aldosterone, plasma volume expansion (dye dilution method), splanchnic blood pooling ((99 m) Tc-RBC SPECT/PET/CT scans), peripheral hypotension, portal hypertension and ascites in brivanib and sorafenib-treated NASH-cirrhotic rats.

CONCLUSION

Besides antifibrotic, antiangiogenic and portal hypertensive effects, chronic antagonism of anti-VEGFR with brivanib and sorafenib improves hepatic blood flow, hepatic venous dysregulation, inhibits leucocytes recruitment/activation, splanchnic blood pooling and ascites formation in NASH-cirrhotic rats. Thus, brivanib and sorafenib might be ideal therapeutic agents in cirrhotic patients suffering from severe haemodynamic disarrangement and ascites.

Acute-on-chronic liver failure: the heart and systemic hemodynamics

PURPOSE OF REVIEW

Circulatory abnormalities in cirrhosis include hyperdynamic circulation and cirrhotic cardiomyopathy. The extent of circulatory abnormalities is further exaggerated in acute-on-chronic liver failure (ACLF). The mechanism remains unclear and management also needs to be evaluated.

RECENT FINDINGS

The predominant mechanism of ACLF is thought to be a systemic inflammatory reaction. Cardiovascular-active factors such as tumor necrosis factor and nitric oxide are increased and cortisol is decreased; the former further dilates the vasculature and the latter decreases the sensitivity to vasoconstrictors. The exaggerated vasodilatation further decreases the cardiac afterload. However, no study has yet demonstrated the benefit of vasodilators/vasoconstrictors in the management of ACLF. Standard medical treatment in this setting is associated with high mortality. Patients treated with molecular adsorbent recirculating system (MARS) had improved serum levels of inflammatory mediators such as tumor necrosis factor alpha and interleukin-6, but this was not associated with improved survival. Liver transplantation eventually reverses the cardiovascular abnormalities.

SUMMARY

Circulatory abnormalities are exaggerated in ACLF. The predominant mechanism is a systemic inflammatory reaction. Modalities such as MARS improve serum markers of inflammation, but not survival. Liver transplantation is the definitive treatment of the cardiovascular abnormalities of ACLF.

Terlipressin and hepatorenal syndrome: What is important for nephrologists and hepatologists

Hepatorenal syndrome (HRS) is a reversible form of functional renal failure that occurs with advanced hepatic cirrhosis and liver failure. Despite mounting research in HRS, its etiology and medical therapy has not been resolved. HRS encompasses 2 distinct types. Type 1 is characterized by the rapid development of renal failure that occurs within 2 wk and involves a doubling of initial serum creatinine. Type 2 has a more insidious onset and is often associated with ascites. Animal studies have shown that both forms, in particular type 1 HRS, are often precipitated by bacterial infections and circulatory changes. The prognosis for HRS remains very poor. Type 1 and 2 both have an expected survival time of 2 wk and 6 mo, respectively. Progression of liver cirrhosis and the resultant portal hypertension leads to the pooling of blood in the splanchnic vascular bed. The ensuing hyperdynamic circulation causes an ineffective circulatory volume which subsequently activates neurohormonal systems. Primarily the sympathetic nervous system and the renin angiotensin system are activated, which, in the early stages of HRS, maintain adequate circulation. Both advanced cirrhosis and prolonged activation of neurohormonal mechanisms result in fatal complications. Locally produced nitric oxide may have the potential to induce a deleterious vasodilatory effect on the splanchnic circulation. Currently medical therapy is aimed at reducing splanchnic vasodilation to resolve the ineffective circulation and maintain good renal perfusion pressure. Terlipressin, a vasopressin analogue, has shown potential benefit in the treatment of HRS. It prolongs both survival time and has the ability to reverse HRS in the majority of patients. In this review we aim to focus on the pathogenesis of HRS and its treatment with terlipressin vs other drugs.

Divergent effects of irritants on the gastric mucosa in rats during various stages after bile duct ligation

BACKGROUND AND AIM

Controversy exists as to whether rats after bile duct ligation (BDL) are more susceptible to gastric mucosal damage (GMD) induced by irritants. In the present study we characterize GMD after intragastric instillation of either ethanol or hydrochloric acid (HCL), 3 and 21 days after the surgical procedure.

METHODS

Bile duct ligation and sham operated (SO) rats were studied.

RESULTS

Three days after surgery, BDL rats exhibited a reduction in gastric mucosal nitric oxide synthase (NOS) activity but an increase in ethanol-induced GMD. Twenty-one days after surgery gastric mucosal prostaglandin (PG) E(2) generation in BDL rats was increased while NOS activity in both groups was similar. Ethanol-induced GMD in SO rats was higher. Pretreatment with NG-nitro-L-arginine methyl ester, prior to ethanol administration was associated with an increase in gastric mucosal PGE(2) generation: (147% in SO and 104% in BDL rats) and in GMD (176% in SO and 303% in BDL rats). HCL induced GMD was of similar magnitude in both groups in both time periods.

CONCLUSIONS

The gastric resistance to damage by irritants in rats with BDL is not a static phenomenon. This may result from sequential changes that occur in the gastric mucosal defense mechanisms during the evolution of liver disease.

Endocannabinoids and liver disease. V. endocannabinoids as mediators of vascular and cardiac abnormalities in cirrhosis

Cirrhosis is associated with marked cardiovascular disturbances. These include hyperdynamic circulation characterized by reduced peripheral vascular resistance and mean arterial pressure and increased cardiac output. Despite the baseline increase in cardiac output, ventricular responsiveness to stimuli is blunted. A number of cellular signaling pathways have been shown to contribute to these abnormalities, including central nervous system cardiovascular dysregulation and humoral factors such as nitric oxide. Endogenous and exogenous cannabinoids have significant cardiovascular effects. Recent evidence suggests that increased activity of the endocannabinoid system at multiple levels contributes to development of both cardiac and vascular changes in cirrhosis. This brief review surveys recent in vivo and in vitro findings in an attempt to highlight the areas of agreement and areas of controversy in the field. The endocannabinoid system affects key cardiovascular regulators, including the autonomic nervous system, cardiac muscle, and vascular smooth muscle. The interplay among these modes of action further complicates interpretation of the in vivo findings. The broad range of cardiovascular actions of endocannabinoids provides ample opportunities for pharmacological manipulation. At the same time, it increases the possibility of undesirable side effects, which need to be carefully evaluated in long-term studies.