Uterine ContractionMyometriumTocolytic AgentsMuscle ContractionOxytocinRitodrineUterusAbortifacient AgentsLabor, ObstetricPregnancyLabor Stage, FirstCoixObstetric Labor, PrematureUterine MonitoringOxytocicsHeart Rate, FetalReceptors, OxytocinParturitionAroclorsLindaneIsometric ContractionLabor OnsetVasotocinDinoprostPregnancy Trimester, ThirdPregnancy, AnimalProstaglandins FMuscle, SmoothLabor, InducedMyocardial ContractionRats, Sprague-DawleyCervix UteriDiltiazemGestational AgeExtraembryonic MembranesCesarean SectionNifedipineMifepristoneUltrasonography, PrenatalDose-Response Relationship, DrugCalciumProgesteroneProstaglandinsEstrusAmniotic FluidPregnancy Trimester, SecondGap JunctionsAlbuterolUltrasonography, DopplerPolychlorinated BiphenylsRats, Inbred StrainsTime FactorsElectric StimulationFetusMuscle, SkeletalIsotonic ContractionVasoconstrictionOvariectomyPlacentaGuinea Pigs