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Dietary calcium and phosphate restriction in guinea-pigs during pregnancy: fetal mineralization induces maternal hypocalcaemia despite increased 1α,25-dihydroxycholecalciferol concentrations

Published online by Cambridge University Press:  09 March 2007

Katrien Rummens*
Affiliation:
Department of Obstetrics and Gynaecology, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
Erik Van Herck
Affiliation:
Laboratorium voor Experimentele Geneeskunde en Endocrinologie, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
Rita van Bree
Affiliation:
Department of Obstetrics and Gynaecology, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
Roger Bouillon
Affiliation:
Laboratorium voor Experimentele Geneeskunde en Endocrinologie, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
F. André Van Assche
Affiliation:
Department of Obstetrics and Gynaecology, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
Johan Verhaeghe
Affiliation:
Department of Obstetrics and Gynaecology, Katholieke Universiteit Leuven, 3000 Leuven, Belgium Laboratorium voor Experimentele Geneeskunde en Endocrinologie, Katholieke Universiteit Leuven, 3000 Leuven, Belgium
*
*Corresponding author: Dr Katrien Rummens, fax +32 16 344205, email [email protected]
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Abstract

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Guinea-pig fetuses at term are mineralized to a degree comparable with human fetuses, which makes the guinea-pig an attractive animal model to study maternal–fetal interactions with regard to Ca and phosphate (P) homeostasis. We studied non-pregnant and pregnant (day 57) vitamin D-replete guinea-pigs, fed either a normal guinea-pig chow with 9·6 g Ca/kg and 4·9 g P/kg or a study diet with 2 g Ca/kg and 1 g P/kg (low-Ca–P diet) for 7–8 weeks. Both pregnancy and the low-Ca–P diet decreased plasma concentrations of 25-hydroxycholecalciferol (25(OH)D3), but increased total and free 1α,25-dihydroxycholecalciferol (1,25(OH)2D3), strongly suggesting an additive stimulation of 1α-hydroxylase activity. Maternal and fetal 25(OH)D3 and 1,25(OH)2D3 levels were highly correlated (r 0·82 and 0·92 respectively, P<0·001). Dual-energy absorption X-ray absorptiometry (DXA) showed that both pregnancy and the low-Ca–P diet decreased bone mineral density (BMD) of the maternal femur, particularly at the distal metaphysis. Despite higher 1,25(OH)2D3 concentrations and lower BMD, pregnant animals on the low-Ca–P diet were hypocalcaemic; blood Ca2+ levels were inversely correlated with the number of fetuses in this group (r -0·93, P<0·001). Fetal growth as well as mineralization (assessed by whole-body and femoral DXA, bone histomorphometry and plasma–bone osteocalcin measurements) were unaltered in the low-Ca–P group. In conclusion, fetal mineralization proceeds normally but induces maternal hypocalcaemia in guinea-pigs with dietary restriction of Ca and P.

Type
Research Article
Copyright
Copyright © The Nutrition Society 2000

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