Differential effects of protein malnutrition in pregnant rats on the expression of placental prolactin-like proteins

Abstract

Summary This study evaluated the effect of chronic protein deficiency during pregnancy on the synthesis of placental lactogen (PL) and prolactin-like proteins (PLPs). Pregnant rats were pair-fed isocaloric diets containing 20% (C) or 5% casein (low protein, LP). In LP animals, maternal weight gain was significantly decreased by 82%, fetal body weight by 20% and placental weight by 30%. These data confirm that this low protein adequate calorie diet results in significant feto-placental growth retardation. Maternal plasma levels of growth hormone (GH), insulin-like growth factor 1 (IGF-1) and thyroid stimulating hormone (TSH) did not significantly differ between C and LP dams, whereas IGF-1 in maternal kidney tissue was significantly higher in LP than in C animals. Placental tissue explants cultured in the presence of [ 35 S]-labeled methionine showed that total secretion of de novo synthesized protein did not differ between C and LP explants. Analysis of secreted proteins by polyacrylamide gel electrophoresis and Western immunoblot procedures revealed that the level of PLP-B immunoreactive protein was significantly decreased by 45% in media from LP placentae, whereas no significant alterations were seen in PLP-C, PL-II or GHRP-1 levels. Northern blot analysis showed a 48% decrease in placental PLP-B steady state mRNA levels in LP animals. Thus, data indicate that a low protein, adequate calorie diet during pregnancy is associated with a selective decrease in PLP-B expression relative to other major secreted placental proteins during late gestation. Evidence further suggests a distinct role for PLP-B in feto-placental growth in this model for intrauterine growth retardation.