Cardiovascular Remodelling Caused by Chronic Hypertension - Coursework Example

CARDIOVASCULAR REMODELLING THAT IS CAUSED BY CHRONIC HYPERTENSION CARDIVASCULAR REMODELLING 7th June, 2012 Abstract Inflammation and oxidative stress are two and closely related physiological processes that generates a chronic pathophysiological body stress, as seen in the cardiovascular remodelling. In an experimental research study, deoxycorticosterone acetate (DOCA) and sodium chloride were administered to DOCA-salt hypertensive rats, with single kidneys (uninephrectomised) to offer reliable animal models of oxidative and inflammatory damage in the cardiovascular system. This was indicated by both the biochemical and pathophysiological changes as well as pharmacological responses from synthetic and natural agents which decreased free oxidative radical molecule concentrations and those abolishing inflammation in the cardiovascular system (Iyer, Chan & Brown 2010). Generally compounds that have the ability to decrease free radicals and inflammatory agents can provide good remedies for these chronic clinical conditions associated with cardiovascular remodelling. These compounds will thus abolish the excessive deposition of collagen and other extracellular matrix proteins in myocardium and vascular endothelium, and ultimately preventing hypertrophy, fibrosis, stiffness and electrical conduction changes in the cardiovascular system. Introduction Hypertension (also referred as high blood pressure) is a chronic pathophysiological stress in the cardiovascular system, and it is a significant cause of generalised cardiovascular remodelling. Chronic high blood pressure without control generates excessive deposition of collagen and other extracellular matrix proteins in myocardium, and ultimately resulting to hypertrophy, fibrosis, stiffness and electrical conduction changes in the heart. In addition, peripheral blood vessels are affected by chronic hypertension which leads to smooth muscle and endothelial dysfunction (Seifi et al., 2007). Prolonged and uncontrolled hypertension leads to activation of the inflammatory reaction and oxidation that generate cardiovascular remodelling in humans. An inflammatory response is a normal defence mechanism by the body immune system cells, expressed whenever they are exposed to infection and injury, but it usually take short period. However, this inflammation process becomes pathological when this mechanism continues for a prolonged period of time. This is because an increased complement factor in the cells results in activation of inflammatory cells such as macrophages, monocytes, T cells, neutrophils, and mast cells in the damaged tissue, as well as the release of inflammatory cytokines. Therefore the infiltration of immunoinflammatory cells enhances the development of cardiovascular remodelling. Oxidative stress which refers to the damage to the cardiovascular cells, induced by reactive oxygen containing free radicals, such as peroxynitrite (ONOO-), superoxide (O2-) and hydroxyl (OH-) which normally exist in form of unpaired electrons may occur. The body cells create oxidative free radicals by enzymes such as cyclooxygenases, myeloperoxidases, lipoxygenases, xanthine oxidase, uncoupled nitric oxide synthase, cytochrome P450, monooxygenase, peroxidases, haeme oxygenases, NADPH oxidases and the enzymes of the mitochondrial electron transport chain (Iyer, Chan & Brown 2010). Superoxide has significant roles which is cell signalling pathways and activate immune cells in the function of normal cells. Superoxide and other oxidative free radicals have the ability to momentarily react with nitric oxide (NO) to produce oxynitrite or generates hydrogen peroxide to create hydroxyl radicals. The free radicals are eliminated by enzymes which includes glutathione peroxidases, superoxide dismutases, thioredoxin reductase and catalase as well as by molecule antioxidants including polyphenol, ascorbic acid and glutathione, which removes these free radical intermediates and inhibit other oxidation reaction (Takimoto and Kass, 2007). These enzymes and molecule antioxidants maintain physiological concentration of superoxide. Therefore, cellular damage is caused by rise in superoxide and oxidative free radicals concentration, and this is produced by decreased removal from the body or increased production in the body. High concentrations of activated tissue inflammatory cells which produces oxygen containing free radicals usually perpetuate oxidative stress. Phospholipase inhibitor (PLAi) is an anti-inflammatory agent which limits the degree of cardiovascular damage caused by inflammatory agents in the body. Chronic hypertension usually results to excessive deposition of collagen fibres (a process referred as fibrosis) in the vascular endothelium and ventricular wall. This causes ventricular hypertrophy and vascular endothelial dysfunction, and eventually remodelling due to a rigid myocardium. The DOCA-salt rat experiment indicates that fibrosis is enhanced by inflammatory processes which arising through involvement of inflammatory cells such as macrophages into peripheral vascular endothelium and smooth muscle organ as well as in the ventricles. This role of inflammatory elements is initiated by a cascade of body reactions that generates arachidonic acid by cell membranes through phospholipid hydrosis sn-2 ester bond. This PLAi prevents the pro-inflammatory enzymes from initiating collagen deposition in the ventricular walls and the endothelium which is a significant component of cardiovascular remodelling of chronic hypertension patients (Levick et al., 2006). Materials and Methods 24 Wistar rats with weights of about 300-350g were taken in this experiment, and the rats aged from eight to ten weeks old. Rats were fed and drank normal food and water for 4 days prior to the date for surgery. The surgery was performed to remove the left kidney from these selected rats (to obtain uninephrectomised rats), and after surgery the rats were divided into three groups. Group one and two were given 1% sodium Chloride in drinking water and a subcutaneous injection of deoxycorticosterone acetate (25 mg in 0.4 mL of dimethylformamide) every fourth day. In addition to this, group one was given DA2 which is treatment in the food, and the second group was given phospholipase inhibitor (PLAi) by oral lavage as treatment every day. Group three which called UNX have been given normal food and normal water without any further treatment and no DOCA injection so as to act as a control fot the experiment. Moreover, the body weight measurements were taken on a daily basis, that is for water initial, water final, food initial and food final. All experiment took 32 days which is 4 days before surgery and 28 days after surgery, and the results for all parameters were recorded. In the experiment the rats were anaesthestised by the administration of Zoletil (which is at 15 mg/kg of tiletamine and 15 mg/kg of zolazepam) via intraperitoneal injection, and the systolic blood pressure was taken, using an MLT844 Pizo-Electric Pulse Transducer (ADInstruments, Sydney, Australia) and inflatable tail-cuff connected to an MLT844 Physiological Pressure Transducer (ADInstruments) and PowerLab data acquisition unit (ADInstruments). Pentobarbitone sodium (100 mg/kg intraperitoneally) was given to rats for euthanization. The buffer was prepared for the Langendroff and organ bath chambers as shown in the constituents below. Preparation of the buffer for Organ Bath Chambers Compound 5L Final Concentration in Tyrode's NaCl 320g 136.9mM KCl 16.1g 5.4mM MgCl2 8.6g 1.05mM NaH2PO4 2.6g 0.42mM NaHCO2 75.9g 22.6mM Mix them in 3500ml of distilled water then add 1500ml of distilled water CaCl2 10.6g 1.8mM The rats were left for about one to two minutes before starting to take organs and blood from them, Heparin (0.1um) was given to the rats through the femoral artery. After that the blood was taken from the abdominal artery, was put into a centrifuge at 5000 rpm for 5 minutes to take plasma. The heart was the first organ to be taken from the rats for langendorff. Thoracic aorta was removed from the rats, and it cleared from the fats then it cut into four rings (4 mm in length). The weights for rats’ organs which are heart, liver, kidney, spleen, perirenal fat, epididymal fat and tibial length were taken for each rat. Furthermore, some of organs took to histology that put in formalin and some of organs to store which putted in freezer. The four rings of thoracic aorta were suspended in an organ bath chamber under a resting tension of ten mN. In addition, the organ bath chamber has been filled with about 20mL of Tyrode’s solution, and the the valve on the aeration line was opened and adjust the flow of the oxygen/carbon dioxide mixture through the aeration frit to create a plume of small bubbles. Then the researcher washed the organ bath until the tension of vessel stable in 10mN. After that, the researcher added to the number two, three and four of organ bath 40ul (2x10-6 ) of noradrenaline which is prestart contraction (70%), and the researcher lifted the curve until it arrived to highest contraction and was also stable. Then noradrenaline was added to organ bath chamber number one; further, sodium nitroprusside was added to organ bath chamber number two, and acetylcholine was added to organ bath chamber three and four by cummulative concentration. Whole data sets were represented as mean _+ standard error of the mean. Comparisons of findings between these rat groups were made via statistical analysis of data sets using 1-way analysis of variance, followed by a suitable post hoc test (Bonferroni) to determine differences between treatment groups. P Read More