Endocannabinoids acting at CB1 receptors mediate the cardiac contractile dysfunction in vivo in cirrhotic rats

Abstract

Advanced liver cirrhosis is associated with hyperdynamic circulation consisting of systemic hypotension, decreased peripheral resistance, and cardiac dysfunction, termed cirrhotic cardiomyopathy. Previous studies have revealed the role of endocannabinoids and vascular CB(1) receptors in the development of generalized hypotension and mesenteric vasodilation in animal models of liver cirrhosis, and CB(1) receptors have also been implicated in the decreased beta-adrenergic responsiveness of isolated heart tissue from cirrhotic rats. Here we document the cardiac contractile dysfunction in vivo in liver cirrhosis and explore the role of the endocannabinoid system in its development. Rats with CCl(4)-induced cirrhosis developed decreased cardiac contractility, as documented through the use of the Millar pressure-volume microcatheter system, low blood pressure, and tachycardia. Bolus intravenous injection of the CB(1) antagonist AM251 (3 mg/kg) acutely increased mean blood pressure, as well as both load-dependent and -independent indexes of systolic function, whereas no such changes were elicited by AM251 in control rats. Furthermore, tissue levels of the endocannabinoid anandamide increased 2.7-fold in the heart of cirrhotic compared with control rats, without any change in 2-arachidonoylglycerol levels, whereas, in the cirrhotic liver, both 2-arachidonoylglycerol (6-fold) and anandamide (3.5-fold) were markedly increased. CB(1)-receptor expression in the heart was unaffected by cirrhosis, as verified by Western blotting. Activation of cardiac CB(1) receptors by endogenous anandamide contributes to the reduced cardiac contractility in liver cirrhosis, and CB(1)-receptor antagonists may be used to improve contractile function in cirrhotic cardiomyopathy and, possibly, in other forms of heart failure.

Fig. 1

Endocannabinoid content of heart and liver from control and cirrhotic rats. Anandamide [arachidonoyl ethanolamide (AEA)] and 2-arachidonoyl glycerol (2-AG) levels in the liver (A) and heart (B) from control (open bars) and cirrhotic rats (shaded bars) are shown. Values are means ± SE; n = 6 in each group. *P < 0.05, compared with corresponding control value.

Fig. 2

Effects of AM251 on hemodynamic parameters. Mean arterial pressure (MAP), heart rate, and cardiac index in control and cirrhotic rats treated with vehicle (open or shaded bars, respectively) or AM251 (3 mg/kg iv, solid bars) are shown. bpm, Beats/min. Values are means ± SE; n = 6–8 rats per group. P < 0.05, *control vs. cirrhotic or #vehicle vs. AM251 value.

Fig. 3

Effects of AM251 on cardiac contractile function. Effect of AM251 on parameters of systolic [left ventricular (LV) end-systolic pressure (LVESP), stroke work, and maximum slope of systolic pressure increment (dP/dt_max)] and diastolic function [LV end- diastolic pressure (LVEDP), minimum slope of systolic pressure increment (dP/dt_min), and relaxation time constant (τ)], measured at 30 min postinjection, is shown. Control and cirrhotic rats were treated with an intravenous bolus of vehicle (open and shaded bars, respectively) or AM251 (3 mg/kg, solid bars). Values are means ± SE; n = 6–8 rats per group. P < 0.05, *control vs. cirrhotic, or #vehicle vs. AM251 value.

Fig. 4

Effects of AM251 on load-independent contractile parameters. A: representative pressure-volume (PV) loops obtained with a P-V conductance catheter system at different preloads are shown. Note that the slope of the end-systolic P-V relation (ESPVR) is less steep in cirrhotic compared with control animals, indicating decreased contractile function, and is acutely increased following treatment of the cirrhotic rats with 3 mg/kg AM251. Effect of AM251 on load-independent contractile parameters measured as maximal cardiac elastance (E_max), ESPVR, preload-recruitable stroke work (PRSW) for systolic (B) and end-diastolic P-V relation (EDPVR) for diastolic function (C) (see METHODS) is shown. Control and cirrhotic animals were treated with vehicle (open and shaded bars, respectively) or 3 mg/kg AM251 (solid bars). Values are means ± SE; n = 6–8 rats per group. P < 0.05, *control vs. cirrhotic, or #vehicle vs. AM251 value.

Fig. 5

Cardiac CB₁-receptor and fatty acid amide hydrolase (FAAH) expressions are unchanged in cirrhosis. Expression of CB₁ receptors and FAAH in the heart of control (n = 4) and cirrhotic rats (n = 4), analyzed by Western blotting (A) and quantified by densitometry (B) is shown. β-Actin was used as loading control. Values are means ± SE. AU, arbitrary unit.