Impaired Milk Folate Secretion is not Corrected by Supplemental Folate during Iron Deficiency in Rats

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Abstract
Decreased milk folate secretion in iron-deficient rat dams contributes to the impairment of folate metabolism in nursing pups. The present study was designed to assess whether impaired milk folate secretion secondary to iron deficiency is due to a decrease in the supply of folate to the mammary gland or to an inability of the mammary gland to effectively use folate. Rats were fed diets containing 0.5, 2.0 or 7.0 mg folate/kg and 8 (-Fe) or 250 (+Fe) mg Fe/kg throughout gestation and until d 17 of lactation. Regardless of dietary Fe content, maternal plasma, red blood cell, liver and kidney folate concentrations correlated with dietary folate content (r = 0.75–0.85, p < 0.0001). With the exception of plasma folate level, which was 46% lower for -Fe than +Fe dams fed 0.5 mg folate/kg, no other differences in indices of folate status were noted between +Fe and -Fe dams. Dietary folate content had a direct impact on milk folate content in +Fe dams but not in -Fe dams. Mammary tissue methionine synthase and folylpolyglutamate synthetase activities were not depressed in Fe deficiency; rather, mean activities were elevated among -Fe dams fed 0.5 mg folate/kg. In conclusion, the reduction in milk folate secretion during Fe deficiency is not due to a decrease in the amount of folate supplied to the mammary gland; rather, the defect causing this reduction is specific to the mammary gland.