Arterioles: The smallest divisions of the arteries located between the muscular arteries and the capillaries.Pia Mater: The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the ARACHNOID and the DURA MATER.Vasodilation: The physiological widening of BLOOD VESSELS by relaxing the underlying VASCULAR SMOOTH MUSCLE.Venules: The minute vessels that collect blood from the capillary plexuses and join together to form veins.Retinal Artery: Central retinal artery and its branches. It arises from the ophthalmic artery, pierces the optic nerve and runs through its center, enters the eye through the porus opticus and branches to supply the retina.Vasoconstriction: The physiological narrowing of BLOOD VESSELS by contraction of the VASCULAR SMOOTH MUSCLE.Microcirculation: The circulation of the BLOOD through the MICROVASCULAR NETWORK.Vasodilator Agents: Drugs used to cause dilation of the blood vessels.Muscle, Smooth, Vascular: The nonstriated involuntary muscle tissue of blood vessels.Cheek: The part of the face that is below the eye and to the side of the nose and mouth.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.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.Juxtaglomerular Apparatus: A complex of cells consisting of juxtaglomerular cells, extraglomerular mesangium lacis cells, the macula densa of the distal convoluted tubule, and granular epithelial peripolar cells. Juxtaglomerular cells are modified SMOOTH MUSCLE CELLS found in the walls of afferent glomerular arterioles and sometimes the efferent arterioles. Extraglomerular mesangium lacis cells are located in the angle between the afferent and efferent glomerular arterioles. Granular epithelial peripolar cells are located at the angle of reflection of the parietal to visceral angle of the renal corpuscle.Microscopy, Video: Microscopy in which television cameras are used to brighten magnified images that are otherwise too dark to be seen with the naked eye. It is used frequently in TELEPATHOLOGY.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.Vasoconstrictor Agents: Drugs used to cause constriction of the blood vessels.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.Capillaries: The minute vessels that connect the arterioles and venules.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.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)Cerebral Arteries: The arterial blood vessels supplying the CEREBRUM.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.Mesoporphyrins: Porphyrins with four methyl, two ethyl, and two propionic acid side chains attached to the pyrrole rings.NG-Nitroarginine Methyl Ester: A non-selective inhibitor of nitric oxide synthase. It has been used experimentally to induce hypertension.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Renal Circulation: The circulation of the BLOOD through the vessels of the KIDNEY.Coronary Vessels: The veins and arteries of the HEART.Arteries: The vessels carrying blood away from the heart.Nitric Oxide Synthase: An NADPH-dependent enzyme that catalyzes the conversion of L-ARGININE and OXYGEN to produce CITRULLINE and NITRIC OXIDE.Swine, Miniature: Genetically developed small pigs for use in biomedical research. There are several strains - Yucatan miniature, Sinclair miniature, and Minnesota miniature.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.Blood Pressure: PRESSURE of the BLOOD on the ARTERIES and other BLOOD VESSELS.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.Mesocricetus: A genus of the family Muridae having three species. The present domesticated strains were developed from individuals brought from Syria. They are widely used in biomedical research.Muscle, Skeletal: A subtype of striated muscle, attached by TENDONS to the SKELETON. Skeletal muscles are innervated and their movement can be consciously controlled. They are also called voluntary muscles.Hydronephrosis: Abnormal enlargement or swelling of a KIDNEY due to dilation of the KIDNEY CALICES and the KIDNEY PELVIS. It is often associated with obstruction of the URETER or chronic kidney diseases that prevents normal drainage of urine into the URINARY BLADDER.Retinal Vessels: The blood vessels which supply and drain the RETINA.Nitric Oxide Synthase Type III: A CALCIUM-dependent, constitutively-expressed form of nitric oxide synthase found primarily in ENDOTHELIAL CELLS.Kidney Glomerulus: A cluster of convoluted capillaries beginning at each nephric tubule in the kidney and held together by connective tissue.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.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)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.Rats, Inbred WKY: A strain of Rattus norvegicus used as a normotensive control for the spontaneous hypertensive rats (SHR).Rats, Inbred SHR: A strain of Rattus norvegicus with elevated blood pressure used as a model for studying hypertension and stroke.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.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).Dose-Response Relationship, Drug: The relationship between the dose of an administered drug and the response of the organism to the drug.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Kidney: Body organ that filters blood for the secretion of URINE and that regulates ion concentrations.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.Rats, 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.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.Hydrazines15-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)Microvessels: The finer blood vessels of the vasculature that are generally less than 100 microns in internal diameter.Angiotensin II: An octapeptide that is a potent but labile vasoconstrictor. It is produced from angiotensin I after the removal of two amino acids at the C-terminal by ANGIOTENSIN CONVERTING ENZYME. The amino acid in position 5 varies in different species. To block VASOCONSTRICTION and HYPERTENSION effect of angiotensin II, patients are often treated with ACE INHIBITORS or with ANGIOTENSIN II TYPE 1 RECEPTOR BLOCKERS.Retinal Vein: Central retinal vein and its tributaries. It runs a short course within the optic nerve and then leaves and empties into the superior ophthalmic vein or cavernous sinus.Cyclic N-Oxides: Heterocyclic compounds in which an oxygen is attached to a cyclic nitrogen.Cyclooxygenase Inhibitors: Compounds or agents that combine with cyclooxygenase (PROSTAGLANDIN-ENDOPEROXIDE SYNTHASES) and thereby prevent its substrate-enzyme combination with arachidonic acid and the formation of eicosanoids, prostaglandins, and thromboxanes.Prostaglandins: A group of compounds derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway. They are extremely potent mediators of a diverse group of physiological processes.Glyburide: An antidiabetic sulfonylurea derivative with actions similar to those of chlorpropamide.Corrosion Casting: A tissue preparation technique that involves the injecting of plastic (acrylates) into blood vessels or other hollow viscera and treating the tissue with a caustic substance. This results in a negative copy or a solid replica of the enclosed space of the tissue that is ready for viewing under a scanning electron microscope.Stress, Mechanical: A purely physical condition which exists within any material because of strain or deformation by external forces or by non-uniform thermal expansion; expressed quantitatively in units of force per unit area.Potassium Channel Blockers: A class of drugs that act by inhibition of potassium efflux through cell membranes. Blockade of potassium channels prolongs the duration of ACTION POTENTIALS. They are used as ANTI-ARRHYTHMIA AGENTS and VASODILATOR AGENTS.Mesentery: A layer of the peritoneum which attaches the abdominal viscera to the ABDOMINAL WALL and conveys their blood vessels and nerves.Pimozide: A diphenylbutylpiperidine that is effective as an antipsychotic agent and as an alternative to HALOPERIDOL for the suppression of vocal and motor tics in patients with Tourette syndrome. Although the precise mechanism of action is unknown, blockade of postsynaptic dopamine receptors has been postulated. (From AMA Drug Evaluations Annual, 1994, p403)Perfusion: Treatment process involving the injection of fluid into an organ or tissue.