Placental CirculationPlacental Function TestsUmbilical ArteriesPlacentaVasoconstrictionPregnancyPulmonary CirculationBlood CirculationVasoconstrictor AgentsRegional Blood FlowVascular ResistanceBlood PressureAnoxiaPulmonary ArteryExtracorporeal CirculationVasodilationArteriolesRenal CirculationHemodynamicsEndothelin-1NorepinephrineSplanchnic CirculationForearmSkin TemperaturePhenylephrineMesenteric ArteriesVasodilator AgentsShiveringVasomotor SystemCoronary CirculationDogsNitric OxideMuscle, Smooth, VascularPerfusionBody Temperature RegulationReceptors, EndothelinSympathetic Nervous SystemAdrenergic alpha-AgonistsArteriesAdrenergic alpha-1 Receptor AgonistsCerebrovascular CirculationEndothelinsDose-Response Relationship, DrugRats, Sprague-DawleyReceptor, Endothelin ACollateral CirculationAdrenergic alpha-AntagonistsAngiotensin IING-Nitroarginine Methyl EsterCoronary Vessels15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic AcidReceptor, Endothelin BBlood Flow VelocityMicrocirculationEndothelium, VascularReceptors, Adrenergic, alphaHeart RateMethoxamineHeadache Disorders, PrimaryLaser-Doppler FlowmetryTyramine