Mesenteric VeinsPortal VeinVeinsPortal SystemHypertension, PortalMesenteric Vascular OcclusionSplenic VeinSaphenous VeinFemoral VeinHepatic VeinsVaricose VeinsRenal VeinsLiver CirculationVenous ThrombosisIliac VeinPulmonary VeinsJugular VeinsSplanchnic CirculationPortal PressurePortasystemic Shunt, SurgicalVena Cava, InferiorEsophageal and Gastric VaricesHepatic ArteryLiverUmbilical VeinsVisceraNorepinephrinePortographyMuscle, Smooth, VascularPancreaticoduodenectomyThrombosisPopliteal VeinTomography, X-Ray ComputedBudd-Chiari SyndromeGastrointestinal HemorrhageMesenteric ArteriesDogsIofetamineAnastomosis, SurgicalMesenteric Artery, SuperiorLiver TransplantationSubclavian VeinCerebral VeinsAdrenergic alpha-2 Receptor AntagonistsHepatectomyAmphetaminesAzygos VeinPhentolamineTreatment OutcomeVascular Surgical ProceduresRetinal VeinPortacaval Shunt, SurgicalLiver NeoplasmsLiver CirrhosisRegional Blood FlowBrachiocephalic VeinsRabbitsTime FactorsVasoconstrictionMuscle ContractionLigationAxillary VeinSplenorenal Shunt, SurgicalRetinal Vein Occlusion