Evidence that somatomedin is synthesized by multiple tissues in the fetus☆

[摘要] Productionofsomatomedin-C,agrowthhormone-dependentpeptidebelievedtomediatethegrowth-promotingactionsofgrowthhormone,hasbeenassessedusingexplantsoffetalmousetissues.Quantitationofthispeptideinmediaofexplantsculturedfor3dayshasbeenaccomplishedwithamembranereceptorassayforsomatomedinandaspecificradioimmunoassayforsomatomedin-C.Somatomedin-Cisproducedbythe11-day-gestationfetalmouseliver,increasesexponentiallyinparallelwithlivergrowthuntilthe16thdayofgestation,andfallspostnatally.Mediasomatomedinisbelievedtobederivedbydenovosynthesissincesalineextractsofliverandmostotherfetaltissuescontainonlyasmallfractionoftheactivityinculturemedia.Theimmunoreactivematerialsecretedintomediaappearstobecloselyrelatedtohumansomatomedin-Csinceitproducesdilutioncurveswhichareparalleltothoseofpurehormone,migratesonSephacryl200atasizesimilartothatofoneofthecomponentsofhumanserumsomatomedin-C,dissociatesintosmallmolecularweightmaterialwithacidtreatment,andisofocusesinarangecomparablewiththatofsomatomedin-Cpurifiedfromhumanserum.Eleven-daylimbbudmesenchymalmicromassculturesand17-day-gestationintestine,heart,brain,kidney,andlungalsosynthesizeimmunoreactivesomatomedin-Cinserum-freemedium.Forthesetissues,themediaactivitywasfarinexcessofthetissueextractableactivity.Somatomedinactivityinexcessofthetissueextractableactivity,however,wasnotfoundinmediafrom17-day-gestationplacenta.Thefindingthatmultipletissuessynthesizesomatomedin-Craisesthepossibilitythattheprimarybiologicalactionsofthishormoneareexertedlocallyatitssitesoforigin.Althoughafunctionofthistypebyapeptidehasnotbeenwidelysuspected,itseemsplausiblethatthecellsoffetaltissuesarecapableofproducinglocalmitogensinmuchthesamemannerasthepostulatedinducersoftissuedifferentiation.

[学科分类] 生物科学（综合）

[关键词] IGF I (II);insulin-like growth factor I (II);MSA;multiplication stimulating activity;BGJB;Bigger's media Jackson-Fitton modication;MBA;membrane binding assay;RIA;radioimmunoassay