（77）

R玉LATIONSHIPOFMETALLOTHIONEINTOZINCMETABOLISM
DURINGPREGNANCY

TAKESHIMINAMIl），TAKASHINAGANUMA2），MARIKOWATANABE3）andHIDEOTAKEMURA3）
1）昆血頻用鳩め抑脚姐肋吻川柳血潮坤塚摘知明朗血〆肋御成勧如戒囁励繭肋血的
2）かゆαγわg乃乃〆0あぶお扇田α乃d砂乃gCめ紗，地相肋血・d拍血椚砂3）穐棚ねW加閻上肋頑はReceivedFebruarylO，2003

Abstract：Theamountsofmetallothionein（MT）andrelatedsubstancesinamniotic
fluid and urine were measured，and the role of the MT containedin these fluids wasstudied．
Amnioticfluid without blood was collected during Caesarian sections．Totalurine
obtainedduringonedaywascollectedfromnewborninfantS0−6dayslandspoturine
wascollectedfrompregnantwomen．Serawerealsocollected．MTinamnioticfluidand
urine was measured by radioimmunoassay．In amniotic fluid，a pOSitive relation wasobserved between MT and L32・microgloblin伽IG），but not between MT and zinc．In
contrast，a pOSitive relation was observed between MTand zincin urine of newborn
infants，but not between MT and MG．Serum Zinclevels were significantlylowerin
postpartumwomen than healthyyoungwomen，and urinary zinclevels weremarkedlyhigherinnewborninfantsthanhealthyyoungwomen．
Inconclusion，thelevelofMTinamnioticfluidmayreflectfetalrenalfunction，andanotherfunctionofMTinthefetusandnewborninfantistosupplementzincinthebody．

Keywords：metallothionein，Zinc，L32−microgloblin，amnioticfluid
mTRODUCTION
The physiologicalstate ofelements such as zinc，iron，and calcium affects the growthand development of the fetus，placenta，and maternal tissues during pregnancyl・2）・The

plasmazincleveldecreasesduringpregnancyandthedeclineisrelatedtothebirthweightor the gestationalage of theinfant3・4）・It was recently reported that zinc supplementationimprovedsurvivalinlow−birth−Weightinfants5）．Therefore，anadequatedietaryintakeofzincduringpregnancyandinfancylSreCOmmended．

Metallothionein（MT）isanacutephase，lowmolecularmass，CySteine・richprotein．MT
isproducedinmostorgansinresponseto metals，Organicsolvents，ultravioletirradiation，

starvationandsoon6）．ItisreportedthatMTfunctionsinthedetoxificationofheavymetals，
storage of essentialmetalslike zinc，SCaVenglng Of free radicals，and cellproliferation6r8）・

MTandZnduringpregnanCy（78）

Duringpregnancy，MTis stainedimmunohistochemicallyinvariousfetaltissues9）．MTmay
haveseveralfunctions duringpregnancy．
Continuousintake of zincis required during pregnancy，aS Zinc deficiency causes
teratogenesis，grOWth retardation，prOlonged parturition and a variety of developmental

disordersin theoffsprlng4）．AndMTacts totransferzincfrom themotherto the fetus10・11）
In addition，Zinc accumulatesin

fetallivers connected with hepatic MT synthesis2）．

FurthermOre，Zincconcentrationinamnioticfluidisrelatedtofetalweight4）andMTmayact
to maintain zinc concentrationin the amnioticfluid．In contrast，Goyerand Cherian12）
reported that MTin placenta acts as a barrier to maternal−fetal cadmium transfer usingCadmium−treated rats，althougha positive relationship between zinc and MTin placentas
WaSfound．ItwasalsoreportedthatMTactedinthedetoxificationofcadmiuminamniotic
fluid since the MTlevelin amniotic fluid reflected theinfluence of tobacco smoke13）・
Therefore，WemeaSured L32−microgloblin（MG）and N−aCetylglutaminidase帥AG）activityinamniotic fluid for observation of renaldysfunction14）and compared them with MTlevels．
TheaimofthepresentstudywastoobservetheroleofMTinthefetusandnewborninfant
byexaminingamnioticfluid，Serumandurine．

MATERIALS ANDMETHODS
The serum，amniotic fluid，and urineusedin the present study were obtained withconsent

fromwomen

whoconsulted

Kosaka

WomensHospital《）saka，Japan）regarding

pregnancy．serumforcontroIwasobtainedfromfemalestudents

h＝14，18−22yearsold）．

Pregnantwomenweredividedintothreegroups：Earlyh＝22，5−21weeks），Middleh＝31，22−28weeksl

andLateh＝24，28−40weeks），andcompared

withcontrol，pOStpartumWOmen

h＝20，2days after parturition），and newborninfants h＝12，076days）．Amniotic fluid
withoutbloodcheckedforalbuminwascollectedduringCaesariansectionh＝12）．Oneday

urinein newborninfants and spot urinein controland pregnantwomen was used．Serum，urine，andamnioticfluidswerestoredat−20℃untiltheexperiments．
MTlevels were measured by radioimmunoassay択IAI zinclevels were measured byinduced coupled plasma atomic emission spectrometry

仕CP−AES），and MGlevels were

measuredbyaturbidityimmunoassaymethod．NAGactivityinamnioticfluidandurinary
Creatininelevels were also measuredus1ng an autOmatic analytical machine for clinical

Chemistry．UrinaryMT，ZincandMGlevelsareshownascreatininelevels．
Datashowthemean±standarderror＄E）．Forstatisticalanalysis，aOne−Wayanalysis
Of variance was used and significance was compared uslng the Student−Neuman−Keurs
method．
RESULTS
Amnioticfluidwithalowalbuminlevel（＜100mg／L）wasusedtoexcludetheeffectsof
blood contaminantsin the present study．MT was detectedin all samples at38．3±5．3
ng／ml，and MG was2489．4±216．9ng／ml．By contrast，the zinclevelwas just O．7±0．1
FLg／ml，andNAGactivitywas8．3±0．4U／1．Apositiverelationshipwas observedbetween
MTandMG

k＝0．682，p＜0．01）asshowninFig．1，butnotbetweenMTandzincorbetween

MTandNAGactivity．

T．Minami，etal．

（79）0004005300032005

つ 乙000︵一∈＼P︶u三「＝0．682（P＜0．01）

1500

◆

◆◆

1000500
0020406080

100MT（ng／ml）
Fig．1．RelationshipbetweenMTandMGinhumanamnioticfluid・Amnioticfluidsh＝12）without

blood

contaminants

werecollected

duringCaesariansection．

Tablel．UrinaryMG，Zinc，andMTlevels
2−MGZncroatinino）／mgcreatinine）

hto

53．6 ±
96．3 ±
156．2 ±
444．9 ±

Newbominfhnt

9364・1±1651・1＊＊＊pく0．05，＊＊pく0．01vS．COntrOlgroup．

ControI
Early
Middlo

6．1
9．9
36．1
91．0

（0．5 ±0．04
1．2 ±0．1
1．2 ±0．1
0．9 ±0．1

17．4 ±
40．7 ±
31．3 ±
22．5 ±

1．5
4．4 ＊
8．0
4．1

mean±S．E．

Tablel shows urinarylevels of MT，Zinc，and MG・The amount of MTin urine
increased significantlyin the Early stage of pregnancy．Highlevels of MT were also
observedin the urine ofnewborninfantS．The amount of MGincreased dependent on thestage ofpregnancy，and very high1evels were observedin the urine ofnewborns・ZinclevelswereshowntopeakattheMiddleperiodofpregnancy，andhighContentofzincwas
alsodetectedintheurineofnewbominfants．ApositiverelationbetweenMTandzincwas
foundin the urine of newborninfants k＝0．574，p＜0．05），but notin pregnant and controI

women．In addition，there was no relation between MT and MGin newborninfants，pregnantwomenorcontroIwomen．
Fig．2shows serum zinclevelsinboth pregnantwomen and newborninfants・Levels
decreasedin the Late stage of pregnancyln COmparison with values for healthy young
women，andafterparturition，decreasedstillmore．

MTandZnduringpregnancy

（80）

302

52051
⁚

0．
﹂

50︵一∈もi︶S一の＞￠一uN∈コLOS≒予≒≒≒予一㌔

Fig．2．ZincconcentrationinserumofpregnantandpostpartumWOmenandinfants．

Controlgroup：femalevolunteers，n＝14，18−22yearsold，Earlygroup：n＝22，5−21
Weeks，Middle group：n＝31，22−28weeks，Late group：n＝24，28−40weeks，
postpartum grOup：n＝20，2days after parturition，neWborninfants：n＝12，0−6

days．厚く0．05vs．controlgroup．

DISCUSSION
Homeostatic conditions for zincin serum are required during pregnancy，eSpeCiallyduringthelasttrimesterandpostpartumasshowninFig．2，aSZincdeficiencyreducesnot
Onlythegrowthoftheplacentaandmatemaltissuesbutalsofetalgrowthanddevelopment
4・15）．However，dietary zincintakeis affected by alcohol，tObacco，drugs，and so on4）．In

addition，ironsupplementationalsoreducestheplasmazincleve116），althoughironisnomallyused toimprove the symptoms of hypochromic anemia，Which occurs sometimes during
pregnanCy．

MTactsintheabsorption，SeCretionandstorageofzincinzinchomeostasis6−8）．Careyet
al．11・17）Observed that enhanced MTlevels reduced zinc transfer from dam to fetus andincreased fetalabnormalitiesuslng ethano卜administered MT−nulland normalmice．ThereissomepossibilitythatzincdeficiencyoccursinthefetuswhenproductionofMTisinduced
in maternaltissues rashly．However，alarge amount of MTis producedin various fetal
OrganS，andasshowninFig．2，urinaryMThadagoodrelationshipwithzincininfanturine．
MTmayactintheabsorption，SeCretionandstorageofzincintheorgansofthefetusand
infant．

Inhumanplacenta，MTwasidentifiedinfetalamnioticcells，SynCytialtrophoblastsand
Villousinterstitialcells，andinmaternaldecidualcells13）．TheMTinplacentaissuggestedto
restrict cadmium and toincrease zinc and copper transportfrom the mother to thefetal
body13・18・19）．In addition，itis speculated that theincrease of MTin human amnioticfluid

T．Minami，etal．

（81）

depends on thelevel of cadmium20・21）・Amniotic fluid consists of fetal urine，When thegestationisover20weeks．TheincreaseinMTinamnioticfluidwaswellcorrelatedwith
thelevelofMG，butnotthezincconcentrationinthepresentstudy．TheincreaseofMTin
amniotic fluidmay reflect not only metalmetabolism but also renalfunction ofthefetus，

althoughWedidnotmeasurecadmiumlevelsinamnioticfluid．Inaddition，theincreaseof
MTlevelinmaternalurinewas not followedby theincrease ofpregnantperiods．Excess
productionofMTmaybecontrolledinmaternalorgans．
In conclusion，itis necessary to observe the zinc concentrationin serum

duringpregnancy，eSpeCiallythelasttrimesterandpostpartum，aSthelevelofzincchangeswiththe
progressionofpregnancyandaszincmayberequiredbythefetusandinfant・Inaddition，MT may beimportantinthefetus andinfant for maintenanCe Ofthe zinc concentration・
AndMTmaybeproducedinthefetalkidneytoprotectthekidney．
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