8-bromocyclic-gmp and Liver-Cirrhosis

Our study determines alterations in the vasoconstrictor response elicited by electric field stimulation (EFS) in mesenteric arteries from cirrhotic rats treated with CCl(4), and how calcitonin gene-related peptide (CGRP) participates in this response. Vasoconstriction induced by EFS was analysed in the absence and presence of the CGRP receptor antagonist CGRP(8-37) in arterial segments from control and cirrhotic rats. The vasodilator response to exogenous CGRP was tested in both groups of rats, and the interference of the guanylate cyclase inhibitor ODQ or the K(ATP) channel blocker glibenclamide was analysed only in segments from cirrhotic rats. The vasodilator response to the K(ATP) channel opener pinacidil and to 8-bromo-cyclic GMP was tested. The K(ATP) currents were recorded using the patch-clamp technique. Expression of receptor activity-modifying protein 1 (RAMP1), calcitonin receptor-like receptor, Kir 6.1 and sulfonylurea receptor 2B (SUR2B) was also analysed. Release of CGRP and cGMP was measured. The EFS-elicited vasoconstriction was less in segments from cirrhotic rats. The presence of CGRP(8-37) increased the EFS-induced response only in segments from cirrhotic rats. The CGRP-induced vasodilatation was greater in segments from cirrhotic rats, and was inhibited by ODQ or glibenclamide. Both pinacidil and 8-bromo-cyclic GMP induced a stronger vasodilator response in segments from cirrhotic rats. Pinacidil induced greater K(ATP) currents in cirrhotic myocytes. Expression of RAMP1, calcitonin receptor-like receptor, Kir 6.1 and SUR2B was not modified by liver cirrhosis. Liver cirrhosis increased CGRP release, but did not modify cGMP formation. The decreased vasoconstrictor response to EFS in cirrhosis is mediated by increased vasodilator response to CGRP, as well as increased K(ATP) channel gating. This effect of CGRP may play a role in the splanchnic vasodilatation present in liver cirrhosis.

Topics: Animals; ATP-Binding Cassette Transporters; Calcitonin Gene-Related Peptide; Calcitonin Gene-Related Peptide Receptor Antagonists; Calcitonin Receptor-Like Protein; Carbon Tetrachloride; Cyclic GMP; Electric Stimulation; Glyburide; KATP Channels; Liver Cirrhosis; Male; Mesenteric Arteries; Muscle Cells; Oxadiazoles; Peptide Fragments; Pinacidil; Potassium Channels, Inwardly Rectifying; Quinoxalines; Rats; Rats, Sprague-Dawley; Receptor Activity-Modifying Protein 1; Receptors, Calcitonin Gene-Related Peptide; Receptors, Drug; Sulfonylurea Receptors; Vasoconstriction; Vasodilation

Portal hypertension, a major complication of cirrhosis, is caused by both increased portal blood flow due to arterial vasodilation and augmented intrahepatic vascular resistance due to sinusoidal constriction. In this study, we examined the possible involvement of resident macrophages in the tone regulation of splanchnic blood vessels using bile duct ligated (BDL) portal hypertensive rats and an in vitro organ culture method. In BDL cirrhosis, the number of ED2-positive resident macrophages increased by two- to fourfold in the vascular walls of the mesenteric artery and extrahepatic portal vein compared with those in sham-operated rats. Many ED1-positive monocytes were also recruited into this area. The expression of inducible nitric oxide (NO) synthase (iNOS) mRNA was increased in the vascular tissues isolated from BDL rats, and accordingly, nitrate/nitrite production was increased. Immunohistochemistry revealed that iNOS was largely expressed in ED1-positive and ED2-positive cells. We further analyzed the effect of iNOS expression on vascular smooth muscle contraction using an in vitro organ culture system. iNOS mRNA expression and nitrate production significantly increased in vascular tissues (without endothelium) incubated with 1 μg/ml lipopolysaccharide (LPS) for 6 h. Immunohistochemistry indicated that iNOS was largely expressed in ED2-positive resident macrophages. α-Adrenergic-stimulated contractility of the mesenteric artery was greatly suppressed by LPS treatment and was restored by N(G)-nitro-L-arginine methyl ester (NO synthase inhibitor); in contrast, portal vein contractility was largely unaffected by LPS. Sodium nitroprusside (NO donor) and 8-bromo-cGMP showed greater contractile inhibition in the mesenteric artery than in the portal vein with decreasing myosin light chain phosphorylation. In the presence of an α-adrenergic agonist, the mesenteric artery cytosolic Ca(2+) level was greatly reduced by sodium nitroprusside; however, the portal vein Ca(2+) level was largely unaffected. These results suggest that the induction of iNOS in monocytes/macrophages contributes to a hypercirculatory state in the cirrhosis model rat in which the imbalance of the responsiveness of visceral vascular walls to NO (mesenteric artery >> portal vein) may account for the increased portal venous flow in portal hypertension.

Topics: Animals; Calcium; Cyclic GMP; Hypertension, Portal; Lipopolysaccharides; Liver Cirrhosis; Macrophages; Male; Mesenteric Arteries; Monocytes; Muscle Contraction; Muscle, Smooth, Vascular; Myosin Light Chains; NG-Nitroarginine Methyl Ester; Nitrates; Nitric Oxide Synthase Type II; Nitroprusside; Portal Vein; Rats; Rats, Sprague-Dawley; Splanchnic Circulation; Vasodilator Agents