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Nitroprusside: A powerful vasodilator used in emergencies to lower blood pressure or to improve cardiac function. It is also an indicator for free sulfhydryl groups in proteins.Ferricyanides: Inorganic salts of the hypothetical acid, H3Fe(CN)6.Vasodilator Agents: Drugs used to cause dilation of the blood vessels.Nitric Oxide Donors: A diverse group of agents, with unique chemical structures and biochemical requirements, which generate NITRIC OXIDE. These compounds have been used in the treatment of cardiovascular diseases and the management of acute myocardial infarction, acute and chronic congestive heart failure, and surgical control of blood pressure. (Adv Pharmacol 1995;34:361-81)Nitric Oxide: A free radical gas produced endogenously by a variety of mammalian cells, synthesized from ARGININE by NITRIC OXIDE SYNTHASE. Nitric oxide is one of the ENDOTHELIUM-DEPENDENT RELAXING FACTORS released by the vascular endothelium and mediates VASODILATION. It also inhibits platelet aggregation, induces disaggregation of aggregated platelets, and inhibits platelet adhesion to the vascular endothelium. Nitric oxide activates cytosolic GUANYLATE CYCLASE and thus elevates intracellular levels of CYCLIC GMP.Vasodilation: The physiological widening of BLOOD VESSELS by relaxing the underlying VASCULAR SMOOTH MUSCLE.Acetylcholine: A neurotransmitter found at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system.Cyclic GMP: Guanosine cyclic 3',5'-(hydrogen phosphate). A guanine nucleotide containing one phosphate group which is esterified to the sugar moiety in both the 3'- and 5'-positions. It is a cellular regulatory agent and has been described as a second messenger. Its levels increase in response to a variety of hormones, including acetylcholine, insulin, and oxytocin and it has been found to activate specific protein kinases. (From Merck Index, 11th ed)Forearm: Part of the arm in humans and primates extending from the ELBOW to the WRIST.Hypotension, Controlled: Procedure in which arterial blood pressure is intentionally reduced in order to control blood loss during surgery. This procedure is performed either pharmacologically or by pre-surgical removal of blood.Endothelium, Vascular: Single pavement layer of cells which line the luminal surface of the entire vascular system and regulate the transport of macromolecules and blood components.omega-N-Methylarginine: A competitive inhibitor of nitric oxide synthetase.NG-Nitroarginine Methyl Ester: A non-selective inhibitor of nitric oxide synthase. It has been used experimentally to induce hypertension.Phenylephrine: An alpha-1 adrenergic agonist used as a mydriatic, nasal decongestant, and cardiotonic agent.Vasoconstrictor Agents: Drugs used to cause constriction of the blood vessels.Nitric Oxide Synthase: An NADPH-dependent enzyme that catalyzes the conversion of L-ARGININE and OXYGEN to produce CITRULLINE and NITRIC OXIDE.Guanylate Cyclase: An enzyme that catalyzes the conversion of GTP to 3',5'-cyclic GMP and pyrophosphate. It also acts on ITP and dGTP. (From Enzyme Nomenclature, 1992) EC 4.6.1.2.Trimethaphan: A nicotinic antagonist that has been used as a ganglionic blocker in hypertension, as an adjunct to anesthesia, and to induce hypotension during surgery.Muscle Relaxation: That phase of a muscle twitch during which a muscle returns to a resting position.Arginine: An essential amino acid that is physiologically active in the L-form.S-Nitroso-N-Acetylpenicillamine: A sulfur-containing alkyl thionitrite that is one of the NITRIC OXIDE DONORS.Blood Pressure: PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Nitroarginine: An inhibitor of nitric oxide synthetase which has been shown to prevent glutamate toxicity. Nitroarginine has been experimentally tested for its ability to prevent ammonia toxicity and ammonia-induced alterations in brain energy and ammonia metabolites. (Neurochem Res 1995:200(4):451-6)Penicillamine: 3-Mercapto-D-valine. The most characteristic degradation product of the penicillin antibiotics. It is used as an antirheumatic and as a chelating agent in Wilson's disease.Enzyme Inhibitors: Compounds or agents that combine with an enzyme in such a manner as to prevent the normal substrate-enzyme combination and the catalytic reaction.OxadiazolesMolsidomine: A morpholinyl sydnone imine ethyl ester, having a nitrogen in place of the keto oxygen. It acts as NITRIC OXIDE DONORS and is a vasodilator that has been used in ANGINA PECTORIS.Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.Vascular Resistance: The force that opposes the flow of BLOOD through a vascular bed. It is equal to the difference in BLOOD PRESSURE across the vascular bed divided by the CARDIAC OUTPUT.Vasoconstriction: The physiological narrowing of BLOOD VESSELS by contraction of the VASCULAR SMOOTH MUSCLE.Nitroglycerin: A volatile vasodilator which relieves ANGINA PECTORIS by stimulating GUANYLATE CYCLASE and lowering cytosolic calcium. It is also sometimes used for TOCOLYSIS and explosives.Bradykinin: A nonapeptide messenger that is enzymatically produced from KALLIDIN in the blood where it is a potent but short-lived agent of arteriolar dilation and increased capillary permeability. Bradykinin is also released from MAST CELLS during asthma attacks, from gut walls as a gastrointestinal vasodilator, from damaged tissues as a pain signal, and may be a neurotransmitter.Baroreflex: A response by the BARORECEPTORS to increased BLOOD PRESSURE. Increased pressure stretches BLOOD VESSELS which activates the baroreceptors in the vessel walls. The net response of the CENTRAL NERVOUS SYSTEM is a reduction of central sympathetic outflow. This reduces blood pressure both by decreasing peripheral VASCULAR RESISTANCE and by lowering CARDIAC OUTPUT. Because the baroreceptors are tonically active, the baroreflex can compensate rapidly for both increases and decreases in blood pressure.Muscle, Smooth, Vascular: The nonstriated involuntary muscle tissue of blood vessels.Aorta, Thoracic: The portion of the descending aorta proceeding from the arch of the aorta and extending to the DIAPHRAGM, eventually connecting to the ABDOMINAL AORTA.Arterioles: The smallest divisions of the arteries located between the muscular arteries and the capillaries.Plethysmography: Recording of change in the size of a part as modified by the circulation in it.Methylene Blue: A compound consisting of dark green crystals or crystalline powder, having a bronze-like luster. Solutions in water or alcohol have a deep blue color. Methylene blue is used as a bacteriologic stain and as an indicator. It inhibits GUANYLATE CYCLASE, and has been used to treat cyanide poisoning and to lower levels of METHEMOGLOBIN.Norepinephrine: Precursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers and of the diffuse projection system in the brain arising from the locus ceruleus. It is also found in plants and is used pharmacologically as a sympathomimetic.Hemodynamics: The movement and the forces involved in the movement of the blood through the CARDIOVASCULAR SYSTEM.Vasomotor System: The neural systems which act on VASCULAR SMOOTH MUSCLE to control blood vessel diameter. The major neural control is through the sympathetic nervous system.Heart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Infusions, Intra-Arterial: Regional infusion of drugs via an arterial catheter. Often a pump is used to impel the drug through the catheter. Used in therapy of cancer, upper gastrointestinal hemorrhage, infection, and peripheral vascular disease.Microcirculation: The circulation of the BLOOD through the MICROVASCULAR NETWORK.PurinonesCromakalim: A potassium-channel opening vasodilator that has been investigated in the management of hypertension. It has also been tried in patients with asthma. (Martindale, The Extra Pharmacopoeia, 30th ed, p352)Mesenteric Arteries: Arteries which arise from the abdominal aorta and distribute to most of the intestines.Arteries: The vessels carrying blood away from the heart.Iontophoresis: Therapeutic introduction of ions of soluble salts into tissues by means of electric current. In medical literature it is commonly used to indicate the process of increasing the penetration of drugs into surface tissues by the application of electric current. It has nothing to do with ION EXCHANGE; AIR IONIZATION nor PHONOPHORESIS, none of which requires current.Nitroso CompoundsRats, Wistar: A strain of albino rat developed at the Wistar Institute that has spread widely at other institutions. This has markedly diluted the original strain.Rats, Sprague-Dawley: A strain of albino rat used widely for experimental purposes because of its calmness and ease of handling. It was developed by the Sprague-Dawley Animal Company.Aorta: The main trunk of the systemic arteries.15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid: A stable prostaglandin endoperoxide analog which serves as a thromboxane mimetic. Its actions include mimicking the hydro-osmotic effect of VASOPRESSIN and activation of TYPE C PHOSPHOLIPASES. (From J Pharmacol Exp Ther 1983;224(1): 108-117; Biochem J 1984;222(1):103-110)Dibutyryl Cyclic GMP: N-(1-Oxobutyl)-cyclic 3',5'-(hydrogen phosphate)-2'-butanoate guanosine. A derivative of cyclic GMP. It has a higher resistance to extracellular and intracellular phosphodiesterase than cyclic GMP.Sympathetic Nervous System: The thoracolumbar division of the autonomic nervous system. Sympathetic preganglionic fibers originate in neurons of the intermediolateral column of the spinal cord and project to the paravertebral and prevertebral ganglia, which in turn project to target organs. The sympathetic nervous system mediates the body's response to stressful situations, i.e., the fight or flight reactions. It often acts reciprocally to the parasympathetic system.Muscle Contraction: A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.Dogs: The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE. They are worldwide in distribution and live in association with people. (Walker's Mammals of the World, 5th ed, p1065)QuinoxalinesCoronary Vessels: The veins and arteries of the HEART.Cyanides: Inorganic salts of HYDROGEN CYANIDE containing the -CN radical. The concept also includes isocyanides. It is distinguished from NITRILES, which denotes organic compounds containing the -CN radical.Pressoreceptors: Receptors in the vascular system, particularly the aorta and carotid sinus, which are sensitive to stretch of the vessel walls.Hypertension: Persistently high systemic arterial BLOOD PRESSURE. Based on multiple readings (BLOOD PRESSURE DETERMINATION), hypertension is currently defined as when SYSTOLIC PRESSURE is consistently greater than 140 mm Hg or when DIASTOLIC PRESSURE is consistently 90 mm Hg or more.Sodium Nitrite: Nitrous acid sodium salt. Used in many industrial processes, in meat curing, coloring, and preserving, and as a reagent in ANALYTICAL CHEMISTRY TECHNIQUES. It is used therapeutically as an antidote in cyanide poisoning. The compound is toxic and mutagenic and will react in vivo with secondary or tertiary amines thereby producing highly carcinogenic nitrosamines.Cyclic GMP-Dependent Protein Kinases: A group of cyclic GMP-dependent enzymes that catalyze the phosphorylation of SERINE or THREONINE residues of proteins.Hydrogen Cyanide: Hydrogen cyanide (HCN); A toxic liquid or colorless gas. It is found in the smoke of various tobacco products and released by combustion of nitrogen-containing organic materials.Rabbits: The species Oryctolagus cuniculus, in the family Leporidae, order LAGOMORPHA. Rabbits are born in burrows, furless, and with eyes and ears closed. In contrast with HARES, rabbits have 22 chromosome pairs.Laser-Doppler Flowmetry: A method of non-invasive, continuous measurement of MICROCIRCULATION. The technique is based on the values of the DOPPLER EFFECT of low-power laser light scattered randomly by static structures and moving tissue particulates.Hypotension: Abnormally low BLOOD PRESSURE that can result in inadequate blood flow to the brain and other vital organs. Common symptom is DIZZINESS but greater negative impacts on the body occur when there is prolonged depravation of oxygen and nutrients.S-Nitrosoglutathione: A sulfur-containing alkyl thionitrite that is one of the NITRIC OXIDE DONORS.Hydroxocobalamin: Injectable form of VITAMIN B 12 that has been used therapeutically to treat VITAMIN B 12 DEFICIENCY.Verapamil: A calcium channel blocker that is a class IV anti-arrhythmia agent.Biological Factors: Endogenously-synthesized compounds that influence biological processes not otherwise classified under ENZYMES; HORMONES or HORMONE ANTAGONISTS.Amino Acid Oxidoreductases: A class of enzymes that catalyze oxidation-reduction reactions of amino acids.Rats, Inbred WKY: A strain of Rattus norvegicus used as a normotensive control for the spontaneous hypertensive rats (SHR).Nitric Oxide Synthase Type III: A CALCIUM-dependent, constitutively-expressed form of nitric oxide synthase found primarily in ENDOTHELIAL CELLS.Muscle, Smooth: Unstriated and unstriped muscle, one of the muscles of the internal organs, blood vessels, hair follicles, etc. Contractile elements are elongated, usually spindle-shaped cells with centrally located nuclei. Smooth muscle fibers are bound together into sheets or bundles by reticular fibers and frequently elastic nets are also abundant. (From Stedman, 25th ed)Indomethacin: A non-steroidal anti-inflammatory agent (NSAID) that inhibits the enzyme cyclooxygenase necessary for the formation of prostaglandins and other autacoids. It also inhibits the motility of polymorphonuclear leukocytes.Potassium Chloride: A white crystal or crystalline powder used in BUFFERS; FERTILIZERS; and EXPLOSIVES. It can be used to replenish ELECTROLYTES and restore WATER-ELECTROLYTE BALANCE in treating HYPOKALEMIA.Injections, Intra-Arterial: Delivery of drugs into an artery.Prostaglandin Endoperoxides, Synthetic: Synthetic compounds that are analogs of the naturally occurring prostaglandin endoperoxides and that mimic their pharmacologic and physiologic activities. They are usually more stable than the naturally occurring compounds.Swine: Any of various animals that constitute the family Suidae and comprise stout-bodied, short-legged omnivorous mammals with thick skin, usually covered with coarse bristles, a rather long mobile snout, and small tail. Included are the genera Babyrousa, Phacochoerus (wart hogs), and Sus, the latter containing the domestic pig (see SUS SCROFA).Coronary Circulation: The circulation of blood through the CORONARY VESSELS of the HEART.Muscle Tonus: The state of activity or tension of a muscle beyond that related to its physical properties, that is, its active resistance to stretch. In skeletal muscle, tonus is dependent upon efferent innervation. (Stedman, 25th ed)Hyperemia: The presence of an increased amount of blood in a body part or an organ leading to congestion or engorgement of blood vessels. Hyperemia can be due to increase of blood flow into the area (active or arterial), or due to obstruction of outflow of blood from the area (passive or venous).Benzopyrans: Compounds with a core of fused benzo-pyran rings.Free Radical Scavengers: Substances that influence the course of a chemical reaction by ready combination with free radicals. Among other effects, this combining activity protects pancreatic islets against damage by cytokines and prevents myocardial and pulmonary perfusion injuries.Adenosine: A nucleoside that is composed of ADENINE and D-RIBOSE. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter.HydrazinesCardiac Output: The volume of BLOOD passing through the HEART per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with STROKE VOLUME (volume per beat).Pulmonary Circulation: The circulation of the BLOOD through the LUNGS.Apamin: A highly neurotoxic polypeptide from the venom of the honey bee (Apis mellifera). It consists of 18 amino acids with two disulfide bridges and causes hyperexcitability resulting in convulsions and respiratory paralysis.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Nitrogen Oxides: Inorganic oxides that contain nitrogen.Rats, Inbred SHR: A strain of Rattus norvegicus with elevated blood pressure used as a model for studying hypertension and stroke.Atrial Natriuretic Factor: A potent natriuretic and vasodilatory peptide or mixture of different-sized low molecular weight PEPTIDES derived from a common precursor and secreted mainly by the HEART ATRIUM. All these peptides share a sequence of about 20 AMINO ACIDS.Isoproterenol: Isopropyl analog of EPINEPHRINE; beta-sympathomimetic that acts on the heart, bronchi, skeletal muscle, alimentary tract, etc. It is used mainly as bronchodilator and heart stimulant.Pulmonary Artery: The short wide vessel arising from the conus arteriosus of the right ventricle and conveying unaerated blood to the lungs.Nitrates: Inorganic or organic salts and esters of nitric acid. These compounds contain the NO3- radical.Antihypertensive Agents: Drugs used in the treatment of acute or chronic vascular HYPERTENSION regardless of pharmacological mechanism. Among the antihypertensive agents are DIURETICS; (especially DIURETICS, THIAZIDE); ADRENERGIC BETA-ANTAGONISTS; ADRENERGIC ALPHA-ANTAGONISTS; ANGIOTENSIN-CONVERTING ENZYME INHIBITORS; CALCIUM CHANNEL BLOCKERS; GANGLIONIC BLOCKERS; and VASODILATOR AGENTS.Nitrites: Salts of nitrous acid or compounds containing the group NO2-. The inorganic nitrites of the type MNO2 (where M=metal) are all insoluble, except the alkali nitrites. The organic nitrites may be isomeric, but not identical with the corresponding nitro compounds. (Grant & Hackh's Chemical Dictionary, 5th ed)Papaverine: An alkaloid found in opium but not closely related to the other opium alkaloids in its structure or pharmacological actions. It is a direct-acting smooth muscle relaxant used in the treatment of impotence and as a vasodilator, especially for cerebral vasodilation. The mechanism of its pharmacological actions is not clear, but it apparently can inhibit phosphodiesterases and it may have direct actions on calcium channels.Methoxamine: An alpha-1 adrenergic agonist that causes prolonged peripheral VASOCONSTRICTION.Phosphodiesterase Inhibitors: Compounds which inhibit or antagonize the biosynthesis or actions of phosphodiesterases.Penis: The external reproductive organ of males. It is composed of a mass of erectile tissue enclosed in three cylindrical fibrous compartments. Two of the three compartments, the corpus cavernosa, are placed side-by-side along the upper part of the organ. The third compartment below, the corpus spongiosum, houses the urethra.DiethylaminesBasilar Artery: The artery formed by the union of the right and left vertebral arteries; it runs from the lower to the upper border of the pons, where it bifurcates into the two posterior cerebral arteries.Potassium Channels: Cell membrane glycoproteins that are selectively permeable to potassium ions. At least eight major groups of K channels exist and they are made up of dozens of different subunits.