​Estriol(1,3,5(10)-estratriene-3,16α,17β-triol;E3)isafemalesexsteroidhormonelargelyassociatedwithpregnancyandfetaldevelopment. FetaladrenalDHEA-Sismetabolizedinthefetalliverto16α-hydroxy-DHEA-S,whichisthenconvertedtoestriolintheplacenta.(1,2) Bythesecondtrimester,about90%oftheestriolproducedisderivedfromthisfetaladrenalDHEA-S.(2) Maternalcirculatingestriollevelsriseprogressivelyduringpregnancy,reachingapeakinthethirdtrimester. Productionofestrioldependsonanintactmaternal-placental-fetalunit,andmaternalsalivaryestriollevelshavebeenusedtomonitorfetalstatusduringpregnancy.(2,3,4,5)EstriolisalsousedaspartoftheTri-orQuad-ScreenTestfordetectionoffetalgeneticdefects.(6,7)

Thephysiologicalrolesofestriolinnon-pregnantwomenarenotwellunderstoodandareunderinvestigation. Withrespecttoestrogenicactivity,estriolisgenerallythoughtobelesspotentthanestrADIolorestrone. However,ithasbeenpointedoutthat,withregardtonongenomicsignalingpathwaysandfunctionalresponsesinthepituitary,estriolisastrongestrogen.(8)

Changesinlevelsofestriolandtheotherestrogensthatoccurduetomenopause,pregnancy,andhormonereplacementtherapyhavealsobeenstudiedextensivelyforrelationshipstocancersusceptibility.(9,10,11,12,13,14) Estriolhasalsobeeninvestigatedforitsrelationtoautoimmunediseasessuchasmultiplesclerosisandsystemiclupuserythematosus,sincepregnantwomenshowsignificantreductionsinsymptomsduringthelasttrimesterofpregnancy.(15,16,17,18.19) Estriolhasalsobeenexaminedforitsroleinboneandlipidmetabolism,anditsfunctionasaprotectiveneurosteroid. (20,21)

Inbloodthemajorityofestriolisboundbyserumproteins,withabout14-16%remainingunbound.(4,22) Unboundestriolenterssalivafrombloodviaintracellularmechanisms,andsalivaryconcentrationscloselyapproximateunboundplasmaconcentrations.(3,23)Thereisvirtuallynoprotein-boundestriolinsaliva.(4)  Correlationbetweenserumandsalivasamplesishighlysignificant.(24)​

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