Down-regulation of the Na+/taurocholate cotransporting polypeptide during pregnancy in the rat.
BACKGROUND
Experimental studies have shown decreased bile acid (BA) uptake and reduced excretion of cholephilic compounds in pregnant rodents.


OBJECTIVE
To assess the expression and function of the main BA importer, the Na(+)/taurocholate cotransporting polypeptide (Ntcp) in pregnant rats.


METHODS
BA uptake and Ntcp expression were studied in control and timed-pregnant rats in late gestation. Ntcp protein, messenger RNA (mRNA) expression, and Ntcp tissue localization were determined by Northern blotting, Western analysis, and tissue immunofluorescence. The activity of three transactivators of the Ntcp promoter: hepatocyte nuclear factor 1-alpha (HNF1-alpha), nuclear receptor heterodimer retinoid X receptor:retinoid acid receptor (RXR:RAR) and signal transducer and activator of transcription 5 (Stat5) was assessed using gel electrophoretic mobility shift assays.


RESULTS
A significantly reduced BA uptake and decreased Ntcp mRNA levels (-40%) and protein mass (-60%) was observed in pregnant rats. Nuclear extracts from pregnant rats showed a marked decrease of HNF1-alpha and RXR:RAR binding activities by -80 and -40% of basal activity, respectively. In contrast, binding activity of Stat-5 was increased by 50% in nuclear extracts from pregnant rats.


CONCLUSIONS
Pregnancy is associated with reduced Ntcp expression and function in the rat. Our findings suggest that Ntcp down-regulation during pregnancy occurs primarily at the transcriptional level.
Arrese
Marco
M
Department of Gastroenterology, Pontificia Universidad Católica de Chile, School of Medicine, Marcoleta # 367, Santiago 6510260, Chile. marrese@med.puc.cl
Trauner
Michael
M
Ananthanarayanan
Meenakshisundaram
M
Pizarro
Margarita
M
Solís
Nancy
N
Accatino
Luigi
L
Soroka
Carol
C
Boyer
James L
JL
Karpen
Saul J
SJ
Miquel
Juan Francisco
JF
Suchy
Frederick J
FJ
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology; D005260:Female; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000502:physiology; D008099:Liver / Q000378:metabolism; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D027981:Symporters; D013656:Taurocholic Acid / Q000493:pharmacokinetics*; D014157:Transcription Factors / Q000378:metabolism; D014316:Tritium
D002352:Carrier Proteins; C093947:MRP2 protein, S cerevisiae; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D012333:RNA, Messenger; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; D027981:Symporters; D014157:Transcription Factors; D014316:Tritium; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid