Placental composition and surface area but not vascularization are altered by maternal protein restriction in the rat.

Amino acids are essential nutrients for foetal growth and development, and maternal protein restriction decreases foetal growth despite increasing placental size. To determine if placental structure is altered so as to impair function despite increased size, the effect of maternal protein restriction on the composition and vascularization of the placenta in the rat was determined. Pregnant rats were randomized to receive either a normal protein (20 per cent) or an isocaloric low (8 per cent) protein diet. Placentae were studied at day 18 of gestation. Tissue sections were stained with biotinylated Bandeiraea simplicifolia (BS-1) lectin to allow identification of foetal capillaries, and analysed using stereological techniques. Protein restriction increased total placental volume, but decreased the proportion of the placental volume composed of labyrinth. Consequently the total volumes of labyrinthine tissue and of foetal and maternal blood space were not different between the two groups. Protein restriction increased the surface area density and total surface area of the materno-foetal interface, but did not alter foetal capillary surface area, diameter or length. This study found that maternal protein restriction is associated with an increase in placental size, and that this enlargement is accompanied by increases in some, but not all, structural correlates of function.