Effect of timing of iron supplementation on maternal and neonatal growth and iron status of iron-deficient pregnant rats

Abstract

We have previously shown that maternal iron (Fe) deficiency not only reduces fetal size, but also increases blood pressure in the offspring when they are adults. In this paper we examine whether there are critical periods when supplementation reverses or fails to reverse the effect both on size and on expression of genes of Fe metabolism. We made dams Fe deficient, mated them and provided supplements of Fe in the diet from the beginning of gestation (0.5 days), from 7.5 days or from 14.5 days. Within 12 h of birth, dams and neonates were killed and tissues taken and examined. Fe deficiency throughout pregnancy reduces neonatal size. Supplementation from the beginning of the first, second or third week all reduced the effect. Maternal haematocrit was restored to normal levels only in animals given supplements for at least 2 weeks. In contrast, the neonates' Fe levels were normal in all supplemented groups. These results were mirrored in liver Fe levels and in transferrin receptor mRNA. Iron-responsive element (IRE)-regulated divalent metal transporter 1 (DMT1) increased in maternal and neonatal liver. Non-IRE-regulated DMT1 levels did not change in the maternal liver, but decreased in the neonatal liver. H and L ferritin mRNA levels also showed different patterns in the mother and her offspring. Finally, the neonatal size correlated with maternal Fe stores, and not with those of the fetus. The data demonstrate that Fe supplementation during pregnancy is most effective when given early, rather than later, in gestation.

Figure 1. The effect of maternal Fe deficiency on maternal haematocrit (A) and haemoglobin (B)

Animals were treated as described in the Methods and the results presented are the means ± s.e.m. of at least 6 animals per group. For dietary details see Methods section. *P < 0.05; **P < 0.01 when compared to the control value by one-way analysis of variance.

Figure 2. The effect of maternal Fe deficiency on haematocrit of neonatal rats

The results are the means ± s.e.m. of pups from at least 6 mothers per group. *P < 0.05; **P < 0.01 when compared to the control value by one-way analysis of variance.

Figure 3. The effect of maternal Fe deficiency on liver Fe levels in the dam (A) and her neonates (B)

The results are the means ± s.e.m. of at least 6 dams or the pups from 6 dams per group. *P < 0.05; **P < 0.01 when compared to the control value by one-way analysis of variance.

Figure 4. The effect of maternal Fe deficiency during pregnancy on TfR mRNA levels in maternal (A) and neonatal livers (B)

Samples were taken and mRNA prepared, reverse transcribed and measured, as described in the Methods. The results are the means ± s.e.m. of livers from at least 6 dams and 6 neonates, each taken from a different litter. *P < 0.05; **P < 0.01 when compared to the control value by Student's unpaired t test.

Figure 5. The effect of maternal Fe deficiency during pregnancy on DMT1 mRNA levels in maternal (A) and neonatal livers (B)

Both the non-IRE-regulated (□) and IRE-regulated forms (▪) were measured. Samples were taken and mRNA prepared, reverse transcribed and measured, as described in the Methods. The results are the means ± s.e.m. of livers from at least 6 dams and 6 offspring, each taken from a different litter. *P < 0.05; **P < 0.01 when compared to the control value by Student's unpaired t test.

Figure 6. The effect of maternal Fe deficiency during pregnancy on ferritin mRNA levels in maternal (A) and neonatal livers (B)

Both L (□) and H ferritin (▪) were measured. Samples were taken and mRNA prepared, reverse transcribed and measured, as described in the Methods. The results are the means ± s.e.m. of livers from at least 6 dams and 6 offspring, each taken from a different litter. *P < 0.05; **P < 0.01 when compared to the control value by Student's unpaired t test.

Figure 7. Maternal and not neonatal liver Fe levels are related to neonatal birthweight

A, the liver Fe level of each mother is related to mean litter weight. Statistical analysis was carried out by linear regression. The dotted lines represent the 95% confidence limits. The slope of the line is significantly different from 0 and the data are correlated at P = 0.0015. B, mean litter liver Fe levels were measured and data correlated to mean litter weight as shown. The slope of the line is not significantly different from 0.