Ossification of the femur in thyroxine-treated tadpoles of Rana pipiens☆

[摘要] TadpolesofRanapipiensatTaylor-KollrosstageIXweretreatedbyimmersioninathyroxinesolutionataconcentrationof6.25×10−8M.Hindlimbsdevelopedprecociously,andalizarin-stainedspecimensshowedthattreatmentwiththyroxineinducedacceleratedossificationoflimbbones.LightmicroscopyofthickEponsectionsshowedthatcartilageandperichondriumwerebeginningtoorganizeinthefemurofnormalanimalsatstageIXandhadbecomeseparatedbyanarrowzoneofosteoidmatrixbystageXI.After4daysofexposuretothyroxine,innerperichondrialcellshadenlargedtobecomeosteoblastsborderingaprominentzoneofosteoidmatrix.By9daysoftreatmentsomeinnerosteoblastswereentirelysurroundedbybonematrixandthushadbecomeosteocytes.Electronmicroscopyrevealedthatroughendoplasmicreticulumbegantoaccumulateinosteoblastsbytheseconddayoftreatment.Fusionofcollagenfibrilswasobservedintheosteoidmatrixofaspecimentreatedfor5days.Depositionofhydroxyapatitecrystalsalongcollagenprotofibrilsinscatteredmineralizationsitesbeganafter6daysoftreatment.Mineralizedsitesgrewandbecameconfluent,sothatby9daysthelowertwo-thirdsofthebonematrixwasalmostcompletelymineralized.Enlargedmineralizationsitesat9daysusuallywereorganizedwithcollagenprotofibrilsintheinteriorandhydroxyapatitecrystalsclusteredaroundtheperipheryofthemineralizingmass.Thyroxineappearstostimulatedifferentiationofosteoblastsfromperichondrialcells.Thehormonemaystimulateosteoblaststosecretedepolymeraseswhichprepareosteoidmatrixformineralizationalongcollagenfibrils.

[学科分类] 生物科学（综合）