ABSTRACT
BACKGROUND/AIMS: Somatostatin has been used for over two decades to treat acute variceal bleeding. Although it is assumed that somatostatin lowers portal pressure by constriction of the splanchnic arteries, little is known about the expression of somatostatin receptors (SSTR) in splanchnic blood vessels. In this study we investigated SSTR expression in splanchnic blood vessels from normal and cirrhotic rats. METHODS/RESULTS: Cirrhosis was induced by intraperitoneal injection of 50 mg thioacetamide twice a week for 14 weeks. In portal vein, mesenteric artery and aorta of normal and cirrhotic rats, mRNA for the five known SSTR was measured by quantitative reverse transcriptase-polymerase chain reaction. SSTR subtypes 1, 2, 3 and 4 were expressed, but subtype 5 was undetectable. In the portal vein of cirrhotic animals, SSTR1 was significantly down-regulated as compared with controls. Otherwise, no major differences in receptor expression between normal and cirrhotic animals were observed. Using immunohistochemistry, we identified all five receptors, although the staining of receptor 5 was very weak. CONCLUSION: All five SSTR are expressed in splanchnic blood vessels. Our results suggest that cirrhosis reduces expression of SSTR1 in portal vein. In other vessels, no major differences between the normal and cirrhotic state were noted.
Subject(s)
Aorta/chemistry , Liver Cirrhosis, Experimental/metabolism , Mesenteric Artery, Superior/chemistry , Portal Vein/chemistry , Receptors, Somatostatin/analysis , Animals , Immunohistochemistry , Liver Cirrhosis, Experimental/chemically induced , Liver Cirrhosis, Experimental/genetics , Liver Cirrhosis, Experimental/pathology , Male , Membrane Proteins/analysis , RNA, Messenger/analysis , Rats , Rats, Wistar , Receptors, Somatostatin/genetics , Reverse Transcriptase Polymerase Chain Reaction , ThioacetamideABSTRACT
BACKGROUND AND PURPOSE: Hyperdynamic circulation and mesenteric hyperaemia are found in cirrhosis. To delineate the role of endocannabinoids in these changes, we examined the cardiovascular effects of anandamide, AM251 (CB(1) antagonist), AM630 (CB(2) antagonist) and capsazepine (VR1 antagonist), in a rat model of cirrhosis. EXPERIMENTAL APPROACH: Cirrhosis was induced by bile duct ligation. Controls underwent sham operation. Four weeks later, diameters of mesenteric arteriole and venule (intravital microscopy), arterial pressure, cardiac output, systemic vascular resistance and superior mesenteric artery (SMA) flow were measured after anandamide, AM251 (with or without anandamide), AM630 and capsazepine administration. CB(1), CB(2) and VR1 receptor expression in SMA was assessed by western blot and RT-PCR. KEY RESULTS: Anandamide increased mesenteric vessel diameter and flow, and cardiac output in cirrhotic rats, but did not affect controls. Anandamide induced a triphasic arterial pressure response in controls, but this pattern differed markedly in cirrhotic rats. Pre-administration of AM251 blocked the effects of anandamide. AM251 (without anandamide) increased arterial pressure and systemic vascular resistance, constricted mesenteric arterioles, decreased SMA flow and changed cardiac output in a time-dependent fashion in cirrhotic rats. Capsazepine decreased cardiac output and mesenteric arteriolar diameter and flow, and increased systemic vascular resistance in cirrhotic rats, but lacked effect in controls. Expression of CB(1) and VR1 receptor proteins were increased in cirrhotic rats. AM630 did not affect any cardiovascular parameter in either group. CONCLUSIONS AND IMPLICATIONS: These data suggest that endocannabinoids contribute to hyperdynamic circulation and mesenteric hyperaemia in cirrhosis, via CB(1)- and VR1-mediated mechanisms.
Subject(s)
Arachidonic Acids/pharmacology , Hyperemia/physiopathology , Liver Cirrhosis, Biliary/physiopathology , Polyunsaturated Alkamides/pharmacology , Receptor, Cannabinoid, CB1/drug effects , Splanchnic Circulation/drug effects , TRPV Cation Channels/drug effects , Vasodilator Agents/pharmacology , Animals , Bile Ducts/surgery , Blood Flow Velocity , Blood Pressure/drug effects , Blotting, Western , Capsaicin/analogs & derivatives , Capsaicin/pharmacology , Cardiac Output/drug effects , Disease Models, Animal , Endocannabinoids , Hyperemia/etiology , Hyperemia/metabolism , Indoles/pharmacology , Liver Circulation/drug effects , Liver Cirrhosis, Biliary/complications , Liver Cirrhosis, Biliary/metabolism , Male , Mesenteric Artery, Superior/chemistry , Mesenteric Artery, Superior/drug effects , Piperidines/pharmacology , Pyrazoles/pharmacology , RNA, Messenger/analysis , Rats , Rats, Sprague-Dawley , Receptor, Cannabinoid, CB1/analysis , Receptor, Cannabinoid, CB1/metabolism , Receptor, Cannabinoid, CB2/drug effects , Reverse Transcriptase Polymerase Chain Reaction , TRPV Cation Channels/analysis , TRPV Cation Channels/metabolism , Time Factors , Vascular Resistance/drug effects , Vasodilation/drug effectsABSTRACT
1. The relationship between nitric oxide (NO) concentration measured with an NO-specific microelectrode and endothelium-dependent relaxation was investigated in isolated rat superior mesenteric artery contracted with 1 microM noradrenaline. 2. Acetylcholine (10 microM) induced endothelium-dependent simultaneous increases in luminal NO concentration of 21 +/- 6 nM, and relaxations with pD2 values and maximum of 6.95 +/- 0.32 and 97.5 +/- 0.7 % (n = 7), respectively. An inhibitor of NO synthase, N G-nitro-L-arginine (L-NOARG, 100 microM) inhibited the relaxations and increases in NO concentration induced by acetylcholine. 3. Oxyhaemoglobin (10 microM) reversed the relaxations and increases in NO concentrations induced by acetylcholine, S-nitroso-N-acetylpenicillamine (SNAP) and S-morpholino-sydnonimine (SIN-1), but not the relaxations induced with forskolin. Oxyhaemoglobin also decreased the NO concentration below baseline level. 4. In the presence of L-NOARG (100 microM), a small relaxation to acetylcholine (10 microM) of noradrenaline-contracted segments was still seen; oxyhaemogobin inhibited this relaxation and decreased the NO concentration by 14 +/- 4 nM (n = 4). 5. The NO concentration-relaxation relationship for acetylcholine resembled that for SNAP and SIN-1 more than for authentic NO. Thus while 7-17 nM NO induced half-maximal relaxations in response to SNAP or SIN-1, 378 +/- 129 nM NO (n = 4) was needed for half-maximal relaxation to authentic NO. 6. The present study provides direct evidence that the relaxation of the rat superior mesenteric artery with the endothelium-dependent vasodilator acetylcholine is correlated to the endogeneous release of NO. The study also suggests that NO mediates the L-NOARG-resistant relaxations in this artery, and that there is a basal NO release.
Subject(s)
Mesenteric Artery, Superior/physiology , Muscle, Smooth, Vascular/physiology , Nitric Oxide/metabolism , Acetylcholine/pharmacology , Animals , Endothelium, Vascular/enzymology , Endothelium, Vascular/physiology , Enzyme Inhibitors/pharmacology , In Vitro Techniques , Male , Mesenteric Artery, Superior/chemistry , Mesenteric Artery, Superior/metabolism , Microelectrodes , Molsidomine/analogs & derivatives , Molsidomine/pharmacology , Muscle Relaxation/physiology , Muscle, Smooth, Vascular/chemistry , Muscle, Smooth, Vascular/metabolism , Nitric Oxide/analysis , Nitric Oxide Donors/pharmacology , Nitric Oxide Synthase/antagonists & inhibitors , Nitric Oxide Synthase Type III , Nitroarginine/pharmacology , Oxyhemoglobins/pharmacology , Penicillamine/analogs & derivatives , Penicillamine/pharmacology , Rats , Rats, Wistar , S-Nitroso-N-AcetylpenicillamineABSTRACT
OBJECTIVE: To test the hypothesis that effects of angiotensin converting enzyme (ACE) inhibitors upon resistance vessel structure are responsible for their ability to cause long-term reduction in blood pressure. DESIGN: Stroke-prone spontaneously hypertensive (SHRSP) and Wistar-Kyoto (WKY) rats were treated with enalapril or hydralazine from 4 to 15 weeks of age. Effects upon tail-cuff blood pressure, left ventricular hypertrophy and structural indices of the superior mesenteric artery (SMA) and its resistance vessels were assessed at 11 weeks of treatment and up to 11 weeks post-treatment. METHODS: Left ventricular hypertrophy was assessed by left ventricular weight:body weight ratios. Evidence of vascular structural change was obtained from tissue weight:body weight ratios, levels of RNA, DNA and expression of alpha-actin and elastin messenger (m)RNA. RESULTS: The effects of enalapril and hydralazine upon left ventricular hypertrophy in SHRSP were consistent with their respective effects upon blood pressure. Both drugs prevented the development of medial hypertrophy in SMA and resistance vessels. This was accompanied by substantial reductions in RNA:DNA ratios. Alpha-actin mRNA levels were not affected by either drug but elastin mRNA levels were reduced by both drugs. During the first 12 days post-treatment there was evidence of structural change in SMA accompanying the increases in blood pressure but importantly not in the resistance vessels. CONCLUSION: The effects of enalapril upon left ventricular hypertrophy and mesenteric arterial hypertrophy are totally consistent with responses to blood pressure and the persistence of structural changes post-treatment does not underlie the ability of the ACE inhibitors to persistently suppress hypertension.