Mesenteric Vascular OcclusionMesenteric Artery, SuperiorMesenteric VeinsReperfusion InjuryTrochlear NerveTrochlear Nerve DiseasesMesenteric ArteriesSuperior Mesenteric Artery SyndromeIntestinesCeliac ArteryIschemiaMesenteric Artery, InferiorPortal VeinSplanchnic CirculationRetinal Artery OcclusionDuodenostomyBrain IschemiaVeinsArteriesRenal VeinsSplenic VeinArterial Occlusive DiseasesPortal SystemInfarction, Middle Cerebral ArteryTomography, X-Ray ComputedMyocardial IschemiaRenal ArterySplenic ArteryAngiographyVisceraCerebral ArteriesTime FactorsVasoconstrictionMuscle, Smooth, VascularRats, Sprague-Dawley